Collection 703p10

Earth science

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Contents Articles Main article Earth science

Earth's spheres Earth

1 1 8 8

Hydrosphere

34

Biosphere

35

Atmosphere

38

Lithosphere

42

Geosphere

45

Pedosphere

45

Cryosphere

50

Magnetosphere

57

Branches of earth science

65

Geology

65

Soil science

85

Oceanography

92

Geography

97

Limnology

106

Glaciology

109

Atmospheric sciences

113

References Article Sources and Contributors

116

Image Sources, Licenses and Contributors

121

Article Licenses License

123

1

Main article Earth science Earth science (also known as geoscience, the geosciences or the Earth sciences) is an all-embracing term for the sciences related to the planet Earth.[1] It is arguably a special case in planetary science, the Earth being the only known life-bearing planet. There are both reductionist and holistic approaches to Earth sciences. The formal discipline of Earth sciences may include the study of the atmosphere, oceans and biosphere, as well as the solid earth. Typically Earth scientists will use tools from physics, chemistry, biology, chronology and mathematics to build a quantitative understanding of how the Earth system works, and how it evolved to its current state.

A volcano eruption is the release of stored energy from below the surface of Earth, originating from radioactive decay and gravitational sorting in the Earth's core and mantle, and residual energy gained [2] during the Earth`s formation.

Fields of study The following fields of science categorized within the geosciences:

are

generally

• Geology describes the rocky parts of the Earth's crust (or lithosphere) and its historic development. Major subdisciplines are mineralogy and petrology, geochemistry, geomorphology, paleontology, stratigraphy, structural geology, engineering geology and sedimentology.[3] [4] • Geophysics and Geodesy investigate the shape of the Earth, its reaction to forces and its magnetic and gravity fields. Geophysicists explore the Earth's core and mantle as well as the tectonic and seismic activity of the lithosphere.[4] [5] [6]

Lava flows from the Kīlauea volcano into the ocean on the Island of Hawaii

• Soil science covers the outermost layer of the Earth's crust that is subject to soil formation processes (or pedosphere).[7] Major subdisciplines include edaphology and pedology.[8]

Earth science • Oceanography and hydrology (includes limnology) describe the marine and freshwater domains of the watery parts of the Earth (or hydrosphere). Major subdisciplines include hydrogeology and physical, chemical, and biological oceanography. • Glaciology covers the icy parts of the Earth (or cryosphere). • Atmospheric sciences cover the gaseous parts of the Earth (or atmosphere) between the surface and the exosphere (about 1000 km). Major subdisciplines are meteorology, climatology, atmospheric chemistry and atmospheric physics. • A very important linking sphere is the biosphere, the study of which is biology. The biosphere consists of all forms of life, from single-celled organisms to pine trees to people. The interactions of Earth's other spheres lithosphere/geosphere, hydrosphere, atmosphere and/or cryosphere and pedosphere - create the conditions that can life.

Earth's interior Plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in of energy transformations in the Earth's crust.[9] Beneath the Earth's crust lies the mantle which is heated by the radioactive decay of heavy elements. The mantle is not quite solid and consists of magma which is in a state of semi-perpetual convection. This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics.[10] [11] [12] [13] Plate tectonics might be thought of as the process by which the earth is resurfaced. Through a process called spreading ridges (or seafloor spreading), new earth crust is created by the flow of magma from underneath the lithosphere to the surface, through fissures, where it cools and solidifies. Through a process called subduction, crust is pushed underground—beneath the rest of the lithosphere—where it comes into with magma and melts—reing the mantle from which it originally came.[11] [13] [14] Areas of the crust where new crust is created are called divergent boundaries, and areas of the crust where it is brought back into the earth are called convergent boundaries.[15] [16] Earthquakes result from the movement of the lithospheric plates, and they often occur near covergent boundaries where parts of the crust are forced into the earth as part of subduction.[17] Volcanoes result primarily from the melting of subducted crust material. Crust material that is forced into the Asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface—giving birth to volcanoes.[11] [17]

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Earth science

3

Earth's electromagnetic field An electromagnet is a magnet that is created by a current that flows around a soft-iron core.[18] Earth has a soft iron inner core surrounded by semi-liquid materials of the outer core that move in continuous currents around the inner core;[19] therefore, the earth is an electromagnet. This is referred to as the dynamo theory of Earth's magnetism.[20] [21]

Atmosphere Earth is blanketed by an atmosphere consisting of 78.0% nitrogen, 20.9% oxygen, and 1% Argon.[22] The atmosphere has five layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere; and 75% of the atmosphere's gases are in the bottom-most layer, the troposphere.[22] The magnetic field created by the internal motions of the core produces the magnetosphere which protects the Earth's atmosphere from the solar wind.[23] As the earth is 4.5 billion years old,[24] it would have lost its atmosphere by now if there were no protective magnetosphere.

The magnetosphere shields the surface of Earth from the charged particles of the solar wind. It is compressed on the day (Sun) side due to the force of the arriving particles, and extended on the night side. (Image not to scale.)

The atmosphere is composed of 78% nitrogen and 21% oxygen. The remaining one percent contains small amounts of other gases including CO2 and water vapors.[22] Water vapors and CO2 allow the Earth's atmosphere to catch and hold the sun's energy through a phenomenon called the greenhouse effect.[25] This allows earth's surface to be warm enough to have liquid water and life. In addition to storing heat, the atmosphere also protects living organisms by shielding the Earth's surface from cosmic rays. Note that the level of protection is high enough to prevent cosmic rays from destroying all life on Earth, yet low enough to aid the mutations that have an important role in pushing forward diversity in the biosphere.

Methodology Like all other scientists, Earth scientists apply the scientific method, taking into a geoethical approach. They formulate hypotheses after observing events and gathering data about natural phenomena, and then they test hypotheses from such data. A contemporary idea within earth science is uniformitarianism. Uniformitarianism says that "ancient geologic features are interpreted by understanding active processes that are readily observed". Simply stated, this means that features of the Earth can be explained by the actions of gradual processes operating over long periods of time; for example, a mountain need not be thought of as having been created in a moment, but instead it may be seen as the result of continuous subduction, causing magma to rise and form continental volcanic arcs.

Earth science

Earth's spheres Earth science generally recognizes four spheres, the lithosphere, the hydrosphere, the atmosphere, and the biosphere[26] ; these correspond to rocks, water, air, and life. Some practitioners include, as part of the spheres of the Earth, the cryosphere (corresponding to ice) as a distinct portion of the hydrosphere, as well as the pedosphere (corresponding to soil) as an active and intermixed sphere.

Partial list of the major earth science topics See: List of basic earth science topics Atmosphere • Atmospheric chemistry • Climatology • Meteorology • Hydrometeorology • Paleoclimatology Biosphere • Biogeography • Paleontology • Palynology • Micropaleontology • Geomicrobiology • Geoarchaeology Hydrosphere • Hydrology • Limnology • Hydrogeology • Oceanography • Chemical oceanography • Marine biology • Marine geology • Paleoceanography • Physical oceanography Lithosphere or geosphere

4

Earth science

5

•

•

Geology • • • •

Economic geology Engineering geology Environmental geology Historical geology

• • • •

• Quaternary geology Planetary geology Sedimentology Stratigraphy Structural geology

Geography •

•

Geophysics • • • • •

•

Glaciology

Physical geography

•

Geochemistry

•

Hydrogeology

•

Geomorphology

•

Mineralogy • •

Pedosphere • Soil science • Edaphology • Pedology Systems • Environmental science • Geography • Human geography • Physical geography • Gaia hypothesis Others • • • • •

Geochronology Geodynamics (see also Tectonics) Geomagnetism Gravimetry (also part of Geodesy) Seismology

Cartography Geoinformatics (GIS) Geostatistics Geodesy and Surveying NASA Earth Science Enterprise

Crystallography Gemology

•

Petrology

•

Speleology

•

Volcanology

Earth science

References [1] Wordnet Search: Earth science (http:/ / wordnetweb. princeton. edu/ perl/ webwn?s=Earth+ science& sub=Search+ WordNet& o2=& o0=1& o7=& o5=& o1=1& o6=& o4=& o3=& h=0) [2] Encyclopedia of Volcanoes, Academic Press, London, 2000 [3] Adams 20 [4] Smith 5 [5] Wordnet Search: Geodesy (http:/ / wordnetweb. princeton. edu/ perl/ webwn?s=geodesy& sub=Search+ WordNet& o2=& o0=1& o7=& o5=& o1=1& o6=& o4=& o3=& h=0) [6] NOAA National Ocean Service Education: Geodesy (http:/ / www. oceanservice. noaa. gov/ education/ kits/ geodesy/ welcome. html) [7] Elissa Levine, 2001, The Pedosphere As A Hub (http:/ / soil. gsfc. nasa. gov/ ped/ pedosph. htm) [8] Duane Gardiner, Lecture: Why Study Soils? excerpted from Miller, R.W. & D.T. Gardiner, 1998. Soils in our Environment, 8th Edition (http:/ / jan. ucc. nau. edu/ ~doetqp-p/ courses/ env320/ lec1/ Lec1. html) [9] Earth's Energy Budget (http:/ / okfirst. ocs. ou. edu/ train/ meteorology/ EnergyBudget. html) [10] Simison par. 7 [11] Adams 94,95,100,102 [12] Smith 13-17,218,G-6 [13] Oldroyd 101,103,104 [14] Smith 327 [15] Smith 316,323-325 [16] There is another type of boundary called a transform boundary where plates slide in opposite directions but no new lithospheric material is created or destroyed (Smith 331). [17] Smith 325,326,329 [18] American 576 [19] The earth has a solid iron inner core surrounded by a liquid outer core (Oldroyd 160). [20] Oldroyd 160 [21] Demorest, Paul (2001-05-21). "Dynamo Theory and Earth's Magnetic Field." (http:/ / setiathome. berkeley. edu/ ~pauld/ etc/ 210BPaper. pdf). . Retrieved 2007-11-17. [22] Adams 107-108 [23] Adams 21-22 [24] Smith 183 [25] American 770 [26] Earth's Spheres (http:/ / www2. cet. edu/ ete/ hilk4/ intro/ spheres. html). ©1997-2000. Wheeling Jesuit University/NASA Classroom of the Future. Retrieved November 11, 2007.

Further reading • Allaby M., 2008. Dictionary of Earth Sciences, Oxford University Press, ISBN 978-0199211944 • Adams, Simon; David Lambert (2006). Earth Science: An illustrated guide to science. New York NY 10001: Chelsea House. pp. 20. earth science. ISBN 0-8160-6164-5. • executive editor, Joseph P. Pickett (1992). American Heritage dictionary of the English language (4th ed.). 222 Berkeley Street, Boston, MA 02116: Houghton Mifflin Company. pp. 572, 770. american. ISBN 0-395-82517-2. • Korvin G., 1998. Fractal Models in the Earth Sciences, Elsvier, ISBN 978-0444889072 • "Earth's Energy Budget" (http://okfirst.mesonet.org/train/meteorology/EnergyBudget.html). Oklahoma Climatological Survey. 1996-2004. Retrieved 2007-11-17. • Miller, George A.; Christiane Fellbaum, and Randee Tengi, and Pamela Wakefield, and Rajesh Poddar, and Helen Langone, and Benjamin Haskell (2006). "WordNet Search 3.0" (http://wordnetweb.princeton.edu/perl/ webwn?s=Earth+science&sub=Search+WordNet&o2=&o0=1&o7=&o5=&o1=1&o6=&o4=&o3=&h=0). WordNet a lexical database for the English language. Princeton University/Cognitive Science Laboratory /221 Nassau St./ Princeton, NJ 08542. Retrieved 2007-11-10. • "NOAA National Ocean Service Education: Geodesy" (http://www.oceanservice.noaa.gov/education/kits/ geodesy/welcome.html). National Oceanic and Atmospheric istration. 2005-03-08. Retrieved 2007-11-17. • Oldroyd, David (2006). Earth Cycles: A historical perspective. Westport, Connicticut: Greenwood Press. earth cycles. ISBN 0-313-33229-0.

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Earth science • Reed, Christina (2008). Earth Science: Decade by Decade. New York, NY: Facts on File. earth-science history during the 20th century. ISBN 978-0816055333. • Simison, W. Brian (2007-02-05). "The mechanism behind plate tectonics" (http://www.ucmp.berkeley.edu/ geology/tecmech.html). Retrieved 2007-11-17. • Smith, Gary A.; Aurora Pun (2006). How Does the Earth Work?. Upper Saddle River, NJ 07458: Pearson Prentice Hall. pp. 5. how does. ISBN 0-13-034129-0. • Tarbuck E. J., Lutgens F. K., and Tasa D., 2002. Earth Science, Prentice Hall, ISBN 978-0130353900 • Yang X. S., 2008. Mathematical Modelling for Earth Sciences, Dunedin Academic Press, ISBN 978-1903765920

External links • Earth Science Picture of the Day (http://epod.usra.edu/), a service of Universities Space Research Association, sponsored by NASA Goddard Space Flight Center. • Geoethics in Planetary and Space Exploration (http://tierra.rediris.es/Geoethics_Planetary_Protection/)].

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Earth's spheres Earth Earth  

"The Blue Marble" photograph of Earth, taken from Apollo 17 Designations Pronunciation

/en-us-earth.oggˈɜrθ/

Adjective

earthly, tellurian, telluric, terran, terrestrial. Orbital characteristics [1]

Epoch J2000.0 Aphelion

152,098,232 km [2] 1.01671388 AU

Perihelion

147,098,290 km [2] 0.98329134 AU

Semi-major axis

149,598,261 km [3] 1.00000261 AU

Eccentricity

0.01671123

Orbital period

365.256363004 days 1.000017421 yr

Average orbital speed

29.78 km/s 107,200 km/h

Mean anomaly

357.51716°

Inclination

7.155° to Sun's equator [6] 1.57869° to invariable plane

[3] [4]

[5]

[5]

Longitude of ascending node 348.73936°[5] [7] Argument of perihelion

[5] [8]

114.20783°

Earth

9 Satellites

1 (the Moon) Physical characteristics [9]

Mean radius

6,371.0 km

Equatorial radius

6,378.1 km

Polar radius

6,356.8 km

Flattening

0.0033528

Circumference

40,075.16 km (equatorial) [12] 40,008.00 km (meridional)

Surface area

510,072,000 km2 148,940,000 km2 land (29.2 %) 361,132,000 km2 water (70.8 %)

Volume

1.08321×1012 km3

Mass

5.9736×1024 kg

Mean density

5.515 g/cm3

Equatorial surface gravity

9.780327 m/s2 0.99732 g

Escape velocity

11.186 km/s

Sidereal rotation period

0.99726968 d 23h 56m 4.100s

Equatorial rotation velocity

1674.4 km/h (465.1 m/s)

Axial tilt

23°26'21".4119

Albedo

0.367 (geometric) [5] 0.306 (Bond)

Surface temp.    Kelvin    Celsius

[10] [11]

[10] [12]

[13] [14] [15]

[5]

[5]

[5] [16]

[5] [17]

[18]

[4] [5]

min

mean [19]

max [20]

[21]

184 K

287.2 K

331 K

-89.2 °C

14 °C

57.8 °C

Atmosphere Surface pressure

101.325 kPa (MSL)

Composition

78.08% nitrogen (N2) 20.95% oxygen (O2) 0.93% argon 0.038% carbon dioxide About 1% water vapor (varies with climate)

[5]

Earth (or the Earth) is the third planet from the Sun and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet, or by its Latin name, Terra.[22] [23]

Earth Home to millions of species including humans, Earth is currently the only astronomical body where life is known to exist.[24] The planet formed 4.54 billion years ago, and life appeared on its surface within a billion years.[25] Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land.[26] The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist during this period. The planet is expected to continue ing life for at least another 500 million years.[27] [28] Earth's outer surface is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. About 71% of the surface is covered with salt water oceans, the remainder consisting of continents and islands which together have many lakes and other sources of water contributing to the hydrosphere. Liquid water, necessary for all known life, is not known to exist in equilibrium on any other planet's surface.[29] Earth's poles are mostly covered with solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap). The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core. Earth interacts with other objects in space, especially the Sun and the Moon. At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis, which is equal to 365.26 solar days, or one sidereal year.[30] The Earth's axis of rotation is tilted 23.4° away from the perpendicular to its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days).[31] Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt and gradually slows the planet's rotation. Between approximately 3.8 billion and 4.1 billion years ago, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment. Both the mineral resources of the planet, as well as the products of the biosphere, contribute resources that are used to a global human population. These inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade, and military action. Human cultures have developed many views of the planet, including personification as a deity, a belief in a flat Earth or in the Earth as the center of the universe, and a modern perspective of the world as an integrated environment that requires stewardship.

Chronology Scientists have been able to reconstruct detailed information about the planet's past. The earliest dated Solar System material was formed 4.5672 ± 0.0006 billion years ago,[32] and by 4.54 billion years ago (within an uncertainty of 1%)[25] the Earth and the other planets in the Solar System had formed out of the solar nebula—a disk-shaped mass of dust and gas left over from the formation of the Sun. This assembly of the Earth through accretion was thus largely completed within 10–20 million years.[33] Initially molten, the outer layer of the planet Earth cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed shortly thereafter, 4.53 billion years ago.[34] The current consensus model[35] for the formation of the Moon is the giant impact hypothesis, in which the Moon was created when a Mars-sized object (sometimes called Theia) with about 10% of the Earth's mass[36] impacted the Earth in a glancing blow.[37] In this model, some of this object's mass would have merged with the Earth and a portion would have been ejected into space, but enough material would have been sent into orbit to coalesce into the Moon. Outgassing and volcanic activity produced the primordial atmosphere of the Earth. Condensing water vapor, augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans.[38] The newly formed Sun was only 70% of its present luminosity, yet evidence shows that the early oceans remained liquid—a contradiction dubbed the faint young Sun paradox. A combination of greenhouse gases and higher levels of solar activity served to raise the Earth's surface temperature, preventing the oceans from freezing over.[39] By 3.5 billion years ago, the Earth's magnetic field was established, which helped

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Earth

11

prevent the atmosphere from being stripped away by the solar wind.[40] Two major models have been proposed for the rate of continental growth:[41] steady growth to the present-day[42] and rapid growth early in Earth history.[43] Current research shows that the second option is most likely, with rapid initial growth of continental crust[44] followed by a long-term steady continental area.[45] [46] [47] On time scales lasting hundreds of millions of years, the surface continually reshaped as continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago (Ma), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 Ma, then finally Pangaea, which broke apart 180 Ma.[48]

Evolution of life At present, Earth provides the only example of an environment that has given rise to the evolution of life.[49] Highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago and half a billion years later the last common ancestor of all life existed.[50] The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and formed a layer of ozone (a form of molecular oxygen [O3]) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes.[51] True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized the surface of Earth.[52] Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 Ma, during the Neoproterozoic, covered much of the planet in a sheet of ice. This hypothesis has been termed "Snowball Earth", and is of particular interest because it preceded the Cambrian explosion, when multicellular life forms began to proliferate.[53] Following the Cambrian explosion, about 535 Ma, there have been five major mass extinctions.[54] The most recent such event was 65 Ma, when an asteroid impact triggered the extinction of the (non-avian) dinosaurs and other large reptiles, but spared some small animals such as mammals, which then resembled shrews. Over the past 65 million years, mammalian life has diversified, and several million years ago an African ape-like animal such as Orrorin tugenensis gained the ability to stand upright.[55] This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which allowed the evolution of the human race. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had,[56] affecting both the nature and quantity of other life forms. The present pattern of ice ages began about 40 Ma and then intensified during the Pleistocene about 3 Ma. High-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 years. The last continental glaciation ended 10,000 years ago.[57]

Future

The life cycle of the Sun

Earth

12

The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will grow by 10% over the next 1.1 Gyr (1.1 billion years) and by 40% over the next 3.5 Gyr.[58] Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the loss of the planet's oceans.[59] The Earth's increasing surface temperature will accelerate the inorganic CO2 cycle, reducing its concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in approximately 500 million[27] to 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years.[60] After another billion years all surface water will have disappeared[28] and the mean global temperature will reach 70 °C[60] (158 °F). The Earth is expected to be effectively habitable for about another 500 million years from that point,[27] although this may be extended up to 2.3 billion years if the nitrogen is removed from the atmosphere.[61] Even if the Sun were eternal and stable, the continued internal cooling of the Earth would result in a loss of much of its CO2 due to reduced volcanism,[62] and 35% of the water in the oceans would descend to the mantle due to reduced steam venting from mid-ocean ridges.[63] The Sun, as part of its evolution, will become a red giant in about 5 Gyr. Models predict that the Sun will expand out to about 250 times its present radius, roughly 1 AU ( km).[58] [64] Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, the Earth will move to an orbit 1.7 AU ( km) from the Sun when the star reaches it maximum radius. The planet was therefore initially expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though most, if not all, remaining life would have been destroyed by the Sun's increased luminosity (peaking at about 5000 times its present level).[58] However, a 2008 simulation indicates that Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's atmosphere and be vaporized.[64]

Composition and structure Earth is a terrestrial planet, meaning that it is a rocky body, rather than a gas giant like Jupiter. It is the largest of the four solar terrestrial planets in size and mass. Of these four planets, Earth also has the highest density, the highest surface gravity, the strongest magnetic field, and fastest rotation.[65] It also is the only terrestrial planet with active plate tectonics.[66]

Shape The shape of the Earth is very close to that of an oblate spheroid, a sphere flattened along the axis from pole to pole such that there is a bulge around the equator.[67] This bulge results from the rotation of the Earth, and causes the diameter at the equator to be 43 km larger than the pole to pole diameter.[68] The average diameter of the reference spheroid is about 12,742 km, which is approximately 40,000 km/π, as the meter was originally defined as 1/10,000,000 of the distance from the equator to the North Pole through Paris, .[69]

Size comparison of inner planets (left to right): Mercury, Venus, Earth and Mars

Local topography deviates from this idealized spheroid, though on a global scale, these deviations are very small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls.[70] The largest local deviations in the rocky surface of the Earth are Mount Everest (8848 m above local sea level) and the Mariana Trench (10,911 m below local sea level). Because of the equatorial bulge, the surface locations farthest from the center of the Earth are the summits of Mount Chimborazo in Ecuador and Huascarán in Peru.[71] [72] [73]

Earth

13

Chemical composition of the crust[74] Compound

Formula

Composition Continental

Oceanic

silica

SiO2

60.2%

48.6%

alumina

Al2O3

15.2%

16.5%

lime

CaO

5.5%

12.3%

magnesia

MgO

3.1%

6.8%

iron(II) oxide

FeO

3.8%

6.2%

sodium oxide

Na2O

3.0%

2.6%

potassium oxide

K2O

2.8%

0.4%

Fe2O3

2.5%

2.3%

water

H2O

1.4%

1.1%

carbon dioxide

CO2

1.2%

1.4%

titanium dioxide

TiO2

0.7%

1.4%

phosphorus pentoxide

P2O5

0.2%

0.3%

99.6%

99.9%

iron(III) oxide

Total

Chemical composition The mass of the Earth is approximately 5.98×1024 kg. It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to mass segregation, the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.[75] The geochemist F. W. Clarke calculated that a little more than 47% of the Earth's crust consists of oxygen. The more common rock constituents of the Earth's crust are nearly all oxides; chlorine, sulfur and fluorine are the only important exceptions to this and their total amount in any rock is usually much less than 1%. The principal oxides are silica, alumina, iron oxides, lime, magnesia, potash and soda. The silica functions principally as an acid, forming silicates, and all the commonest minerals of igneous rocks are of this nature. From a computation based on 1,672 analyses of all kinds of rocks, Clarke deduced that 99.22% were composed of 11 oxides (see the table at right). All the other constituents occur only in very small quantities.[76]

Internal structure The interior of the Earth, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties, but unlike the other terrestrial planets, it has a distinct outer and inner core. The outer layer of the Earth is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity, and the thickness of the crust varies: averaging 6 km under the oceans and 30–50 km on the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, and it is of the lithosphere that the tectonic plates are comprised. Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 kilometers below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core.[77] The inner core may rotate at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year.[78]

Earth

14

Geologic layers of the Earth[79] [80] Depth km Component Layer

Earth cutaway from core to exosphere. Not to scale.

Density g/cm3

[81]

0–60

Lithosphere

—

0–35

Crust

[82]

2.2–2.9

35–60

Upper mantle

3.4–4.4

35–2890

Mantle

3.4–5.6

100–700

Asthenosphere

—

2890–5100 Outer core

9.9–12.2

5100–6378 Inner core

12.8–13.1

Heat Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%).[83] The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232.[84] At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa.[85] Because much of the heat is provided by radioactive decay, scientists believe that early in Earth history, before isotopes with short half-lives had been depleted, Earth's heat production would have been much higher. This extra heat production, twice present-day at approximately 3 billion years ago,[83] would have increased temperature gradients within the Earth, increasing the rates of mantle convection and plate tectonics, and allowing the production of igneous rocks such as komatiites that are not formed today.[86]

Present-day major heat-producing isotopes[87] Isotope

Heat release W/kg isotope

Half-life years

Mean mantle concentration kg isotope/kg mantle

Heat release W/kg mantle

238

9.46 × 10−5

4.47 × 109

30.8 × 10−9

2.91 × 10−12

235

U

5.69 × 10−4

7.04 × 108

0.22 × 10−9

1.25 × 10−13

232

Th

2.64 × 10−5

1.40 × 1010

124 × 10−9

3.27 × 10−12

2.92 × 10−5

1.25 × 109

36.9 × 10−9

1.08 × 10−12

U

40

K

The mean heat loss from the Earth is 87 mW m−2, for a global heat loss of 4.42 × 1013 W.[88] A portion of the core's thermal energy is transported toward the crust by mantle plumes; a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts.[89] More of the heat in the Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs in the oceans because the crust there is much thinner than that of the continents.[90]

Earth

15

Tectonic plates Earth's main plates[91]

Plate name

[92]

Area 106 km2

African Plate

78.0

Antarctic Plate

60.9

Indo-Australian Plate

47.2

Eurasian Plate

67.8

North American Plate

75.9

South American Plate

43.6

Pacific Plate

103.3

The mechanically rigid outer layer of the Earth, the lithosphere, is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: Convergent boundaries, at which two plates come together, Divergent boundaries, at which two plates are pulled apart, and Transform boundaries, in which two plates slide past one another laterally. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur along these plate boundaries.[93] The tectonic plates ride on top of the asthenosphere, the solid but less-viscous part of the upper mantle that can flow and move along with the plates,[94] and their motion is strongly coupled with convection patterns inside the Earth's mantle. As the tectonic plates migrate across the planet, the ocean floor is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes continually recycles the oceanic crust back into the mantle. Because of this recycling, most of the ocean floor is less than 100 million years in age. The oldest oceanic crust is located in the Western Pacific, and has an estimated age of about 200 million years.[95] [96] By comparison, the oldest dated continental crust is 4030 million years old.[97] Other notable plates include the Indian Plate, the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. The Australian Plate fused with the Indian Plate between 50 and 55 million years ago. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/yr[98] and the Pacific Plate moving 52–69 mm/yr. At the other extreme, the slowest-moving plate is the Eurasian Plate, progressing at a typical rate of about 21 mm/yr.[99]

Surface The Earth's terrain varies greatly from place to place. About 70.8%[100] of the surface is covered by water, with much of the continental shelf below sea level. The submerged surface has mountainous features, including a globe-spanning mid-ocean ridge system, as well as undersea volcanoes,[68] oceanic trenches, submarine canyons, oceanic plateaus and abyssal plains. The remaining 29.2% not covered by water consists of mountains, deserts, plains, plateaus, and other geomorphologies.

Earth The planetary surface undergoes reshaping over geological time periods because of tectonics and erosion. The surface features built up or deformed through plate tectonics are subject to steady weathering from precipitation, thermal cycles, and chemical effects. Glaciation, coastal erosion, the build-up of coral reefs, and large meteorite impacts[101] also act to reshape the landscape. The continental crust consists of lower density material such as the igneous rocks granite and andesite. Less common is basalt, a denser volcanic rock that is the primary constituent of the ocean floors.[103] Sedimentary rock is formed from the accumulation of sediment that becomes compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form only about 5% of the crust.[104] The third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types Present day Earth altimetry and bathymetry. Data from the National Geophysical [102] Data Center's TerrainBase Digital Terrain Model . through high pressures, high temperatures, or both. The most abundant silicate minerals on the Earth's surface include quartz, the feldspars, amphibole, mica, pyroxene and olivine.[105] Common carbonate minerals include calcite (found in limestone) and dolomite.[106] The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. Currently the total arable land is 13.31% of the land surface, with only 4.71% ing permanent crops.[14] Close to 40% of the Earth's land surface is presently used for cropland and pasture, or an estimated 1.3×107 km2 of cropland and 3.4×107 km2 of pastureland.[107] The elevation of the land surface of the Earth varies from the low point of −418 m at the Dead Sea, to a 2005-estimated maximum altitude of 8,848 m at the top of Mount Everest. The mean height of land above sea level is 840 m.[108]

16

Earth

Hydrosphere The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from others in the Solar System. The Earth's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m. The deepest underwater location is Challenger Deep of the Mariana Trench in the Pacific Ocean with a depth of −10,911.4 m.[109] [110] The mass of the oceans is approximately 1.35×1018 metric tons, or about 1/4400 of the total mass of the Earth. The oceans Elevation histogram of the surface of the Earth cover an area of 3.618×108 km2 with a mean depth of 3,682 m, resulting in an estimated volume of 1.332×109 km3.[111] If all the land on Earth were spread evenly, water would rise to an altitude of more than 2.7 km.[112] About 97.5% of the water is saline, while the remaining 2.5% is fresh water. Most fresh water, about 68.7%, is currently ice.[113] The average salinity of the Earth's oceans is about 35 grams of salt per kilogram of sea water (35 ‰).[114] Most of this salt was released from volcanic activity or extracted from cool, igneous rocks.[115] The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms.[116] Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir.[117] Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño-Southern Oscillation.[118]

Atmosphere The atmospheric pressure on the surface of the Earth averages 101.325 kPa, with a scale height of about 8.5 km.[5] It is 78% nitrogen and 21% oxygen, with trace amounts of water vapor, carbon dioxide and other gaseous molecules. The height of the troposphere varies with latitude, ranging between 8 km at the poles to 17 km at the equator, with some variation resulting from weather and seasonal factors.[119] Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 billion years ago, forming the primarily nitrogen-oxygen atmosphere of today. This change enabled the proliferation of aerobic organisms as well as the formation of the ozone layer which blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life on Earth include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature.[120] This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Carbon dioxide, water vapor, methane and ozone are the primary greenhouse gases in the Earth's atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C and life would likely not exist.[100]

17

Earth

18

Weather and climate The Earth's atmosphere has no definite boundary, slowly becoming thinner and fading into outer space. Three-quarters of the atmosphere's mass is contained within the first 11 km of the planet's surface. This lowest layer is called the troposphere. Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower density air then rises, and is replaced by cooler, higher density air. The result is atmospheric circulation that drives the weather and climate through redistribution of heat energy.[121]

Satellite cloud cover image of Earth using NASA's Moderate-Resolution Imaging Spectroradiometer.

The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°.[122] Ocean currents are also important factors in determining climate, particularly the thermohaline circulation that distributes heat energy from the equatorial oceans to the polar regions.[123] Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and settles to the surface as precipitation.[121] Most of the water is then transported to lower elevations by river systems and usually returned to the oceans or deposited into lakes. This water cycle is a vital mechanism for ing life on land, and is a primary factor in the erosion of surface features over geological periods. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topological features and temperature differences determine the average precipitation that falls in each region.[124] The amount of solar energy reaching the Earth's decreases with increasing latitude. At higher latitudes the sunlight reaches the surface at a lower angles and it must through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level decreases by about 0.4°C per per degree of latitude away from the equator.[125] The Earth can be sub-divided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, temperate and polar climates.[126] Climate can also be classified based on the temperature and precipitation, with the climate regions characterized by fairly uniform air masses. The commonly used Köppen climate classification system (as modified by Wladimir Köppen's student Rudolph Geiger) has five broad groups (humid tropics, arid, humid middle latitudes, continental and cold polar), which are further divided into more specific subtypes.[122] Upper atmosphere Above the troposphere, the atmosphere is usually divided into the stratosphere, mesosphere, and thermosphere.[120] Each layer has a different lapse rate, defining the rate of change in temperature with height. Beyond these, the exosphere thins out into the magnetosphere, where the Earth's magnetic fields interact with the solar wind.[127] Within the stratosphere is the ozone layer, a component that partially shields the surface from ultraviolet light and thus is important for life on Earth. The Kármán line, defined as 100 km above the Earth's surface, is a working definition for the boundary between atmosphere and space.[128]

This view from orbit shows the full Moon partially obscured and deformed by the Earth's atmosphere. NASA image.

Thermal energy causes some of the molecules at the outer edge of the Earth's atmosphere have their velocity increased to the point where they can escape from the planet's gravity. This results in a slow but steady leakage of the atmosphere into space. Because unfixed hydrogen has a low molecular weight, it can achieve escape velocity more readily and it leaks into outer space at a greater rate than other

Earth gasses.[129] The leakage of hydrogen into space contributes to the pushing of the Earth from an initially reducing state to its current oxidizing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is believed to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere.[130] Hence the ability of hydrogen to escape from the Earth's atmosphere may have influenced the nature of life that developed on the planet.[131] In the current, oxygen-rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.[132]

Magnetic field The Earth's magnetic field is shaped roughly as a magnetic dipole, with the poles currently located proximate to the planet's geographic poles. At the equator of the magnetic field, the magnetic field strength at the planet's surface is 3.05 × 10−5 T, with global magnetic dipole moment of 7.91 × 1015 T m3.[133] According to dynamo theory, the field is generated within the molten outer core region where heat creates convection motions of conducting materials, generating electric currents. These in turn produce the Earth's magnetic field. The convection movements in the core are chaotic; the magnetic poles drift and Schematic of Earth's magnetosphere. The solar wind flows from left to right periodically change alignment. This results in field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.[134] [135] The field forms the magnetosphere, which deflects particles in the solar wind. The sunward edge of the bow shock is located at about 13 times the radius of the Earth. The collision between the magnetic field and the solar wind forms the Van Allen radiation belts, a pair of concentric, torus-shaped regions of energetic charged particles. When the plasma enters the Earth's atmosphere at the magnetic poles, it forms the aurora.[136]

19

Earth

Orbit and rotation Rotation Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time (86,400.0025 SI seconds).[137] As the Earth's solar day is now slightly longer than it was during the 19th century because of tidal acceleration, each day varies between 0 and 2 SI ms longer.[138] [139] Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86164.098903691 seconds of mean solar time (UT1), or 23h 56m 4.098903691s. [4] [140] Earth's rotation period relative to the precessing or moving mean vernal equinox, misnamed its Earth's axial tilt (or obliquity) and its relation to the rotation axis and plane of orbit. sidereal day, is 86164.09053083288 seconds of h m mean solar time (UT1) (23 56 s [4] 4.09053083288 ). Thus the sidereal day is shorter than the stellar day by about 8.4 ms.[141] The length of the mean solar day in SI seconds is available from the IERS for the periods 1623–2005[142] and 1962–2005.[143] Apart from meteors within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in the Earth's sky is to the west at a rate of 15°/h = 15'/min. For bodies near the celestial equator, this is equivalent to an apparent diameter of the Sun or Moon every two minutes; from the planet's surface, the apparent sizes of the Sun and the Moon are approximately the same.[144] [145]

Orbit Earth orbits the Sun at an average distance of about 150 million kilometers every 365.2564 mean solar days, or one sidereal year. From Earth, this gives an apparent movement of the Sun eastward with respect to the stars at a rate of about 1°/day, or a Sun or Moon diameter every 12 hours. Because of this motion, on average it takes 24 hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the meridian. The orbital speed of the Earth averages about 30 km/s (108,000 km/h), which is fast enough to cover the planet's diameter (about 12,600 km) in seven minutes, and the distance to the Moon (384,000 km) in four hours.[5] The Moon revolves with the Earth around a common barycenter every 27.32 days relative to the background stars. When combined with the Earth–Moon system's common revolution around the Sun, the period of the synodic month, from new moon to new moon, is 29.53 days. Viewed from the celestial north pole, the motion of Earth, the Moon and their axial rotations are all counter-clockwise. Viewed from a vantage point above the north poles of both the Sun and the Earth, the Earth appears to revolve in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.5 degrees from the perpendicular to the Earth–Sun plane, and the Earth–Moon plane is tilted about 5 degrees against the Earth-Sun plane. Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses.[5] [146] The Hill sphere, or gravitational sphere of influence, of the Earth is about 1.5 Gm (or 1,500,000 kilometers) in radius.[147] [148] This is maximum distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit the Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.

20

Earth

21

Earth, along with the Solar System, is situated in the Milky Way galaxy, orbiting about 28,000 light years from the center of the galaxy. It is currently about 20 light years above the galaxy's equatorial plane in the Orion spiral arm.[149]

Axial tilt and seasons Because of the axial tilt of the Earth, the amount of sunlight reaching any given point on the surface varies over the course of the year. This results in seasonal change in climate, with summer in the northern hemisphere occurring when the North Pole is pointing toward the Sun, and winter taking place when the pole is pointed away. During the Illustration of the Milky Way Galaxy, showing summer, the day lasts longer and the Sun climbs higher in the sky. In the location of the Sun winter, the climate becomes generally cooler and the days shorter. Above the Arctic Circle, an extreme case is reached where there is no daylight at all for part of the year—a polar night. In the southern hemisphere the situation is exactly reversed, with the South Pole oriented opposite the direction of the North Pole. By astronomical convention, the four seasons are determined by the solstices—the point in the orbit of maximum axial tilt toward or away from the Sun—and the equinoxes, when the direction of the tilt and the direction to the Sun are perpendicular. In the northern hemisphere, Winter Solstice occurs on about December 21, Summer Solstice is near June 21, Spring Equinox is around March 20 and Autumnal Equinox is about September 23. In the Southern hemisphere, the situation is reversed, with the Summer and Winter Solstices exchanged and the Spring and Autumnal Equinox dates switched.[150] The angle of the Earth's tilt is relatively stable over long periods of time. However, the tilt does undergo nutation; a slight, irregular motion Earth and Moon from Mars, imaged by Mars with a main period of 18.6 years.[151] The orientation (rather than the Reconnaissance Orbiter. From space, the Earth angle) of the Earth's axis also changes over time, precessing around in can be seen to go through phases similar to the a complete circle over each 25,800 year cycle; this precession is the phases of the Moon. reason for the difference between a sidereal year and a tropical year. Both of these motions are caused by the varying attraction of the Sun and Moon on the Earth's equatorial bulge. From the perspective of the Earth, the poles also migrate a few meters across the surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. The rotational velocity of the Earth also varies in a phenomenon known as length of day variation.[152] In modern times, Earth's perihelion occurs around January 3, and the aphelion around July 4. However, these dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. The changing Earth-Sun distance results in an increase of about 6.9%[153] in solar energy reaching the Earth at perihelion relative to aphelion. Since the southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, the southern hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. However, this effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of water in the southern hemisphere.[154]

Earth

22

Moon Characteristics Diameter

3,474.8 km

Mass

7.349×1022 kg

Semi-major axis 384,400 km Orbital period

27 d 7 h 43.7 m

The Moon is a relatively large, terrestrial, planet-like satellite, with a diameter about one-quarter of the Earth's. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger relative to the dwarf planet Pluto. The natural satellites orbiting other planets are called "moons" after Earth's Moon. The gravitational attraction between the Earth and Moon causes tides on Earth. The same effect on the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit the Earth. As a result, it always presents the same face to the planet. As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases; the dark part of the face is separated from the light part by the solar terminator. Because of their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm a year. Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23 µs a year—add up to significant changes.[155] During the Devonian period, for example, (approximately 410 million years ago) there were 400 days in a year, with each day lasting 21.8 hours.[156] The Moon may have dramatically affected the development of life by moderating the planet's climate. Paleontological evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon.[159] Some theorists believe that without this stabilization against the torques applied by the Sun and planets to the Earth's equatorial bulge, the rotational axis might be chaotically unstable, exhibiting chaotic changes over millions of years, as appears to be the case for Mars.[160] Details of the Earth-Moon system. Besides the radius of each object, the radius to

[157] Viewed from Earth, the Moon is just far the Earth-Moon barycenter is shown. Photos from NASA . Data from NASA [158] enough away to have very nearly the same . The Moon's axis is located by Cassini's third law. apparent-sized disk as the Sun. The angular size (or solid angle) of these two bodies match because, although the Sun's diameter is about 400 times as large as the Moon's, it is also 400 times more distant.[145] This allows total and annular solar eclipses to occur on Earth.

The most widely accepted theory of the Moon's origin, the giant impact theory, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. This hypothesis explains (among other things) the Moon's relative lack of iron and volatile elements, and the fact that its composition is nearly identical to that of the Earth's crust.[161] Earth has at least two co-orbital asteroids, 3753 Cruithne and 2002 AA29.[162]

Earth

23

A scale representation of the relative sizes of, and average distance between, Earth and Moon

Habitability A planet that can sustain life is termed habitable, even if life did not originate there. The Earth provides the (currently understood) requisite conditions of liquid water, an environment where complex organic molecules can assemble, and sufficient energy to sustain metabolism.[163] The distance of the Earth from the Sun, as well as its orbital eccentricity, rate of rotation, axial tilt, geological history, sustaining atmosphere and protective magnetic field all contribute to the conditions believed necessary to originate and sustain life on this planet.[164]

Biosphere The planet's life forms are sometimes said to form a "biosphere". This biosphere is generally believed to have begun evolving about 3.5 billion years ago. Earth is the only place where life is known to exist. The biosphere is divided into a number of biomes, inhabited by broadly similar plants and animals. On land, biomes are separated primarily by differences in latitude, height above sea level and humidity. Terrestrial biomes lying within the Arctic or Antarctic Circles, at high altitudes or in extremely arid areas are relatively barren of plant and animal life; species diversity reaches a peak in humid lowlands at equatorial latitudes.[165]

Natural resources and land use The Earth provides resources that are exploitable by humans for useful purposes. Some of these are non-renewable resources, such as mineral fuels, that are difficult to replenish on a short time scale. Large deposits of fossil fuels are obtained from the Earth's crust, consisting of coal, petroleum, natural gas and methane clathrate. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed in Earth's crust through a process of Ore genesis, resulting from actions of erosion and plate tectonics.[166] These bodies form concentrated sources for many metals and other useful elements. The Earth's biosphere produces many useful biological products for humans, including (but far from limited to) food, wood, pharmaceuticals, oxygen, and the recycling of many organic wastes. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land.[167] Humans also live on the land by using building materials to construct shelters. In 1993, human use of land is approximately: Land use Percentage

Arable land Permanent crops Permanent pastures Forests and woodland Urban areas Other 13.13%

[14]

4.71%

[14]

26%

The estimated amount of irrigated land in 1993 was 2,481,250 km2.[14]

32%

1.5%

30%

Earth

Natural and environmental hazards Large areas of the Earth's surface are subject to extreme weather such as tropical cyclones, hurricanes, or typhoons that dominate life in those areas. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, and other calamities and disasters. Many localized areas are subject to human-made pollution of the air and water, acid rain and toxic substances, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion, erosion, and introduction of invasive species. According to the United Nations, a scientific consensus exists linking human activities to global warming due to industrial carbon dioxide emissions. This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather and a global rise in average sea levels.[168]

Human geography Cartography, the study and practice of map making, and vicariously geography, have historically been the disciplines devoted to depicting the Earth. Surveying, the determination of locations and distances, and to a lesser extent navigation, the determination of position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information. Earth has approximately 6,803,000,000 human inhabitants as of December 12, 2009.[169] Projections indicate that the world's human population will reach seven billion in 2013 and 9.2 billion in 2050.[170] Most of the growth is expected to take place in developing nations. Human population density varies widely around the world, but a majority live in Asia. By 2020, 60% of the world's population is expected to be living in urban, rather than rural, areas.[171] It is estimated that only one-eighth of the surface of the Earth is suitable for humans to live on—three-quarters is covered by oceans, and half of the land area is either desert (14%),[172] high mountains (27%),[173] or other less suitable terrain. The northernmost permanent settlement in the world is Alert, on Ellesmere Island in Nunavut, Canada.[174] (82°28′N) The southernmost is the Amundsen-Scott South Pole Station, in Antarctica, almost exactly at the South Pole. (90°S)

24

Earth

Independent sovereign nations claim the planet's entire land surface, except for some parts of Antarctica and the odd unclaimed area of Bir Tawil between Egypt and Sudan. As of 2007 there are 201 sovereign states, including the 192 United Nations member states. In addition, there are 59 dependent territories, and a number of autonomous areas, territories under dispute and other entities.[14] Historically, Earth has never had a sovereign government with authority over the entire globe, although a number of nation-states have striven for world domination and failed.[175]

25

The Earth at night, a composite of DMSP/OLS ground illumination data on a simulated night-time image of the world. This image is not photographic and many features are brighter than they would appear to a direct observer.

The United Nations is a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict.[176] It is not, however, a world government. The U.N. serves primarily as a forum for international diplomacy and international law. When the consensus of the hip permits, it provides a mechanism for armed intervention.[177] The first human to orbit the Earth was Yuri Gagarin on April 12, 1961.[178] In total, about 400 people visited outer space and reached Earth orbit as of 2004, and, of these, twelve have walked on the Moon.[179] [180] [181] Normally the only humans in space are those on the International Space Station. The station's crew, currently six people, is usually replaced every six months.[182] The furthest humans have travelled from Earth is 400,171 km, achieved during the 1970 Apollo 13 mission.[183]

Cultural viewpoint The name "Earth" derives from the Anglo-Saxon word erda, which means ground or soil, and is related to the German word erde. It became eorthe later, and then erthe in Middle English.[184] The standard astronomical symbol of the Earth consists of a cross circumscribed by a circle.[185] Unlike the rest of the planets in the Solar System, humankind did not begin to view the Earth as a moving object in orbit around the Sun until the 16th century.[186] Earth has often been personified as a deity, in particular a goddess. In many cultures the mother goddess is also portrayed as a fertility deity. Creation myths in many religions recall a story involving the creation of the Earth by a supernatural deity or The first photograph ever taken by astronauts of deities. A variety of religious groups, often associated with an "Earthrise", from Apollo 8 fundamentalist branches of Protestantism[187] or Islam,[188] assert that their interpretations of these creation myths in sacred texts are literal truth and should be considered alongside or replace conventional scientific s of the formation of the Earth and the origin and development of life.[189] Such assertions are opposed by the scientific community[190] [191] and by other religious groups.[192] [193] [194] A prominent example is the creation-evolution controversy. In the past there were varying levels of belief in a flat Earth,[195] but this was displaced by the concept of a spherical Earth due to observation and circumnavigation.[196] The human perspective regarding the Earth has changed following the advent of spaceflight, and the biosphere is now widely viewed from a globally integrated

Earth perspective.[197] [198] This is reflected in a growing environmental movement that is concerned about humankind's effects on the planet.[199]

Notes [1] All astronomical quantities vary, both secularly and periodically. The quantities given are the values at the instant J2000.0 of the secular variation, ignoring all periodic variations. [2] aphelion = a × (1 + e); perihelion = a × (1 - e), where a is the semi-major axis and e is the eccentricity. [3] Standish, E. Myles; Williams, James C. "Orbital Ephemerides of the Sun, Moon, and Planets" (http:/ / iau-comm4. jpl. nasa. gov/ XSChap8. pdf) (PDF). International Astronomical Union Commission 4: (Ephemerides). . Retrieved 2010-04-03. See table 8.10.2. Calculation based upon 1 AU = 149,597,870,700(3) m. [4] Staff (2007-08-07). "Useful Constants" (http:/ / hpiers. obspm. fr/ eop-pc/ models/ constants. html). International Earth Rotation and Reference Systems Service. . Retrieved 2008-09-23. [5] Williams, David R. (2004-09-01). "Earth Fact Sheet" (http:/ / nssdc. gsfc. nasa. gov/ planetary/ factsheet/ earthfact. html). NASA. . Retrieved 2010-08-09. [6] Allen, Clabon Walter; Cox, Arthur N. (2000). Allen's Astrophysical Quantities (http:/ / books. google. com/ ?id=w8PK2XFLLH8C& pg=PA294). Springer. p. 294. ISBN 0387987460. . [7] The reference lists the longitude of the ascending node as -11.26064°, which is equivalent to 348.73936° by the fact that any angle is equal to itself plus 360°. [8] The reference lists the longitude of perihelion, which is the sum of the longitude of the ascending node and the argument of perihelion. That is, 114.20783° + (-11.26064°) = 102.94719°. [9] Various (2000). David R. Lide. ed. Handbook of Chemistry and Physics (81st ed.). CRC. ISBN 0849304814. [10] IERS Working Groups (2003). "General Definitions and Numerical Standards" (http:/ / www. iers. org/ MainDisp. csl?pid=46-25776). In McCarthy, Dennis D.; Petit, Gérard. IERS Technical Note No. 32. U.S. Naval Observatory and Bureau International des Poids et Mesures. . Retrieved 2008-08-03. [11] Cazenave, Anny (1995). "Geoid, Topography and Distribution of Landforms" (http:/ / web. archive. org/ web/ 20061016024803/ http:/ / www. agu. org/ reference/ gephys/ 5_cazenave. pdf). In Ahrens, Thomas J (PDF). Global earth physics a handbook of physical constants. Washington, DC: American Geophysical Union. ISBN 0-87590-851-9. Archived from the original (http:/ / www. agu. org/ reference/ gephys/ 5_cazenave. pdf) on 2006-10-16. . Retrieved 2008-08-03. [12] Rosenberg, Matt. "What is the circumference of the earth?" (http:/ / geography. about. com/ library/ faq/ blqzcircumference. htm). About.com. . Retrieved 2010-04-22. [13] Pidwirny, Michael (2006-02-02). Surface area of our planet covered by oceans and continents.(Table 8o-1) (http:/ / www. physicalgeography. net/ fundamentals/ 8o. html). University of British Columbia, Okanagan. . Retrieved 2007-11-26. [14] Staff (2008-07-24). "World" (https:/ / www. cia. gov/ library/ publications/ the-world-factbook/ geos/ xx. html). The World Factbook. Central Intelligence Agency. . Retrieved 2008-08-05. [15] Due to natural fluctuations, ambiguities surrounding ice shelves, and mapping conventions for vertical datums, exact values for land and ocean coverage are not meaningful. Based on data from the Vector Map and Global Landcover (http:/ / www-gem. jrc. it/ ) datasets, extreme values for coverage of lakes and streams are 0.6% and 1.0% of the earth's surface. The ice shields of Antarctica and Greenland are counted as land, even though much of the rock which s them lies below sea level. [16] Yoder, Charles F. (1995). T. J. Ahrens. ed. Global Earth Physics: A Handbook of Physical Constants (http:/ / web. archive. org/ web/ 20070308141029/ http:/ / www. agu. org/ reference/ gephys. html). Washington: American Geophysical Union. p. 12. ISBN 0875908519. Archived from the original (http:/ / www. agu. org/ reference/ gephys. html) on 2007-03-08. . Retrieved 2007-03-17. [17] Allen, Clabon Walter; Cox, Arthur N. (2000). Allen's Astrophysical Quantities (http:/ / books. google. com/ ?id=w8PK2XFLLH8C& pg=PA296). Springer. p. 296. ISBN 0387987460. . Retrieved 2010-08-17. [18] Arthur N. Cox, ed (2000). Allen's Astrophysical Quantities (http:/ / books. google. com/ ?id=w8PK2XFLLH8C& pg=PA244) (4th ed.). New York: AIP Press. p. 244. ISBN 0-387-98746-0. . Retrieved 2010-08-17. [19] "World: Lowest Temperature" (http:/ / wmo. asu. edu/ world-lowest-temperature). WMO Weather and Climate Extremes Archive. Arizona State University. . Retrieved 2010-08-07. [20] Kinver, Mark (December 10, 2009). "Global average temperature may hit record level in 2010" (http:/ / news. bbc. co. uk/ 2/ hi/ science/ nature/ 8406839. stm). BBC Online. . Retrieved 2010-04-22. [21] "World: Highest Temperature" (http:/ / wmo. asu. edu/ world-highest-temperature). WMO Weather and Climate Extremes Archive. Arizona State University. . Retrieved 2010-08-07. [22] "Blue Planet" is used as the title of two films (Blue Planet and The Blue Planet), in the Life issue "The Incredible Year '68", which featured the Earthrise photo with lines (http:/ / yalepress. yale. edu/ yupbooks/ excerpts/ poole_earthrise. pdf) from poet James Dickey ("Behold/The blue planet steeped in its dream/Of reality"), and in the title of the European Space Agency bulletin report Exploring the water cycle of the 'Blue Planet' (http:/ / www. esa. int/ esapub/ bulletin/ bulletin137/ bul137b_drinkwater. pdf). [23] By International Astronomical Union convention, the term terra is used only for naming extensive land masses on celestial bodies other than the Earth. Cf. Blue, Jennifer (2007-07-05). "Descriptor (Feature Types)" (http:/ / planetarynames. wr. usgs. gov/ jsp/ append5. jsp). Gazetteer of Planetary Nomenclature. USGS. . Retrieved 2007-07-05.

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Earth [161] Canup, R.; Asphaug, E. (2001). "Origin of the Moon in a giant impact near the end of the Earth's formation". Nature 412 (6848): 708–712. doi:10.1038/35089010. PMID 11507633. [162] Whitehouse, David (2002-10-21). "Earth's little brother found" (http:/ / news. bbc. co. uk/ 1/ hi/ sci/ tech/ 2347663. stm). BBC News. . Retrieved 2007-03-31. [163] Staff (September 2003). "Astrobiology Roap" (http:/ / astrobiology. arc. nasa. gov/ roap/ g1. html). NASA, Lockheed Martin. . Retrieved 2007-03-10. [164] Dole, Stephen H. (1970). Habitable Planets for Man (http:/ / www. rand. org/ pubs/ reports/ R414/ ) (2nd ed.). American Elsevier Publishing Co. ISBN 0-444-00092-5. . Retrieved 2007-03-11. [165] Hillebrand, Helmut (2004). "On the Generality of the Latitudinal Gradient". American Naturalist 163 (2): 192–211. doi:10.1086/381004. PMID 14970922. [166] Staff (2006-11-24). "Mineral Genesis: How do minerals form?" (http:/ / www. utexas. edu/ tmm/ npl/ mineralogy/ mineral_genesis/ ). Non-vertebrate Paleontology Laboratory, Texas Memorial Museum. . Retrieved 2007-04-01. [167] Rona, Peter A. (2003). "Resources of the Sea Floor" (http:/ / www. sciencemag. org/ cgi/ content/ full/ 299/ 5607/ 673?ijkey=AHVbRrqUsmdHY& keytype=ref& siteid=sci). Science 299 (5607): 673–674. doi:10.1126/science.1080679. PMID 12560541. . Retrieved 2007-02-04. [168] Staff (2007-02-02). "Evidence is now 'unequivocal' that humans are causing global warming – UN report" (http:/ / www. un. org/ apps/ news/ story. asp?NewsID=21429& Cr=climate& Cr1=change). United Nations. . Retrieved 2007-03-07. [169] United States Census Bureau (2008-01-07). "World POP Clock Projection" (http:/ / www. census. gov/ ipc/ www/ popclockworld. html). United States Census Bureau International Database. . Retrieved 2008-01-07. [170] Staff. "World Population Prospects: The 2006 Revision" (http:/ / www. un. org/ esa/ population/ publications/ wpp2006/ wpp2006. htm). United Nations. . Retrieved 2007-03-07. 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A World Designed by God: Science and Creationism in Contemporary Islam (http:/ / www2. truman. edu/ ~edis/ writings/ articles/ CFI-2001. pdf). Amherst: Prometheus. ISBN 1-59102-064-6. . Retrieved 2008-04-28. [189] Ross, M.R. (2005). "Who Believes What? Clearing up Confusion over Intelligent Design and Young-Earth Creationism" (http:/ / www. nagt. org/ files/ nagt/ jge/ abstracts/ Ross_v53n3p319. pdf) (PDF). Journal of Geoscience Education 53 (3): 319. . Retrieved 2008-04-28. [190] Pennock, R. T. (2003). "Creationism and intelligent design". Annual Review of Genomics Human Genetics 4: 143–63. doi:10.1146/annurev.genom.4.070802.110400. PMID 14527300. [191] Science, Evolution, and Creationism (http:/ / books. nap. edu/ openbook. php?record_id=11876& page=R1). Washington, D.C: National Academies Press. 2008. ISBN 0-309-10586-2. .

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Earth [192] Colburn,, A.; Henriques, Laura (2006). "Clergy views on evolution, creationism, science, and religion". Journal of Research in Science Teaching 43 (4): 419–442. doi:10.1002/tea.20109. [193] Frye, Roland Mushat (1983). Is God a Creationist? The Religious Case Against Creation-Science. Scribner's. ISBN 0-68417-993-8. [194] Gould, S. J. (1997). "Nonoverlapping magisteria" (http:/ / www. jbburnett. com/ resources/ gould_nonoverlapping. pdf) (PDF). Natural History 106 (2): 16–22. . Retrieved 2008-04-28. [195] Russell, Jeffrey B. "The Myth of the Flat Earth" (http:/ / www. asa3. org/ ASA/ topics/ history/ 1997Russell. html). American Scientific Affiliation. . Retrieved 2007-03-14.; but see also Cosmas Indicopleustes. [196] Jacobs, James Q. (1998-02-01). "Archaeogeodesy, a Key to Prehistory" (http:/ / www. jqjacobs. net/ astro/ aegeo. html). . Retrieved 2007-04-21. [197] Fuller, R. Buckminster (1963). [[Operating Manual for Spaceship Earth (http:/ / www. futurehi. net/ docs/ OperatingManual. html)]] (First ed.). New York: E.P. Dutton & Co. ISBN 0-525-47433-1. . Retrieved 2007-04-21. [198] Lovelock, James E. (1979). Gaia: A New Look at Life on Earth (First ed.). Oxford: Oxford University Press. ISBN 0-19-286030-5. [199] For example: McMichael, Anthony J. (1993). Planetary Overload: Global Environmental Change and the Health of the Human Species. Cambridge University Press. ISBN 0521457599.

References Further reading • Comins, Neil F. (2001). Discovering the Essential Universe (http://adsabs.harvard.edu/abs/2003deu..book... ..C) (Second ed.). W. H. Freeman. ISBN 0-7167-5804-0. Retrieved 2007-03-17.

External links • • • •

USGS Geomagnetism Program (http://geomag.usgs.gov/) NASA Earth Observatory (http://earthobservatory.nasa.gov/) Audio—Cain/Gay (2007) Astronomy Cast (http://www.astronomycast.com/stars/episode-51-earth/) Earth Earth Profile (http://solarsystem.nasa.gov/planets/profile.cfm?Object=Earth) by NASA's Solar System Exploration (http://solarsystem.nasa.gov/) • Climate changes cause Earth's shape to change – NASA (http://www.nasa.gov/centers/goddard/earthandsun/ earthshape.html) • The Gateway to Astronaut Photography of Earth (http://eol.jsc.nasa.gov/Coll/weekly.htm) • Global Measured Extremes of Temperature and Precipitation (http://www.ncdc.noaa.gov/oa/climate/ globalextremes.html) National Climatic Data Center pfl:Erd rue:Земля (планета)

33

Hydrosphere

Hydrosphere A hydrosphere (from Greek ὕδωρ - hydor, "water" and σφαῖρα - sphaira, "sphere") in physical geography describes the combined mass of water found on, under, and over the surface of a planet. The total mass of the Earth's hydrosphere is about 1.4 × 1018 tonnes, which is about 0.023% of the Earth's total mass. About 20 × 1012 tonnes of this is in the Earth's atmosphere (the volume of one tonne of water is approximately 1 cubic metre). Approximately 75% of the Earth's surface, an area of some 361 million square The movement of water around, over, and through the Earth is called the water kilometres (139.5 million square miles), is cycle, a key process of the hydrosphere. covered by ocean. The average salinity of the Earth's oceans is about 35 grams of salt per kilogram of sea water (35 ‰).[1]

Other hydrospheres A thick hydrosphere is thought to exist around the Jovian moon Europa. The outer layer of this hydrosphere is almost entirely ice, but current models predict that there is an ocean up to 100 km in depth underneath the ice. This ocean remains in a liquid form because of tidal flexing of the moon in its orbit around Jupiter. The volume of Europa's hydrosphere is 3 × 1018 m3, 2.3 times that of Earth. It has been suggested that the Jovian moon Ganymede and the Saturnian moon Enceladus may also possess sub-surface oceans. However the ice covering is expected to be thicker on Jupiter's Ganymede than on Europa.

Hydrological cycle Insolation, or energy (in the form of heat and light) from the sun, provides the energy necessary to cause evaporation from all wet surfaces including oceans, rivers, lakes, soil and the leaves of plants. Water vapor is further released as transpiration from vegetation and from humans and other animals.

References [1] Kennish, Michael J. (2001). Practical handbook of marine science. Marine science series (3rd ed.). CRC Press. p. 35. ISBN 0849323916.

External links • Ground Water - USGS (http://capp.water.usgs.gov/GIP/gw_gip/index.html)

34

Biosphere

35

Biosphere Our biosphere is the global sum of all ecosystems. It can also be called the zone of life on Earth, a closed (apart from solar and cosmic radiation) and self-regulating system.[1] From the broadest biophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, hydrosphere and atmosphere. The biosphere is postulated to have evolved, beginning through a process of biogenesis or biopoesis, at least some 3.5 billion years ago.[2]

A false-color composite of global oceanic and terrestrial photoautotroph abundance, from September 1997 to August 2000. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE.

In a broader sense; biospheres are any closed, self-regulating systems containing ecosystems; including artificial ones such as Biosphere 2 and BIOS-3; and, potentially, ones on other planets or moons.[3]

Origin and use of the term The term "biosphere" was coined by geologist Eduard Suess in 1875, which he defined as:[4] "The place on Earth's surface where life dwells." While this concept has a geological origin, it is an indication of the impact of both Darwin and Maury on the earth sciences. The biosphere's ecological context comes from the 1920s (see Vladimir I. Vernadsky), preceding the 1935 introduction of the term "ecosystem" by Sir Arthur Tansley (see ecology history). Vernadsky defined ecology as the science of the biosphere. It is an interdisciplinary concept for integrating astronomy, geophysics, meteorology, biogeography, evolution, geology, geochemistry, hydrology and, generally speaking, all life and earth sciences.

Gaia hypothesis The concept that the biosphere is itself a living organism, either actually or metaphorically, is known as the Gaia hypothesis. James Lovelock, an atmospheric scientist from the United Kingdom, proposed the Gaia hypothesis to explain how biotic and abiotic factors interact in the biosphere. This hypothesis considers Earth itself a kind of living organism. Its atmosphere, geosphere, and hydrosphere are cooperating systems that yield a biosphere full of life. In the early 1970s, Lynn Margulis, a microbiologist from the United States, added to the hypothesis, specifically noting the ties between the biosphere and other Earth systems. For example, when carbon dioxide levels increase in the atmosphere, plants grow more quickly. As their growth continues, they remove more and more carbon dioxide from the atmosphere. Many scientists are now involved in new fields of study that examine interactions between biotic and abiotic factors in the biosphere, such as geobiology and geomicrobiology. Ecosystems occur when communities and their physical environment work together as a system. The difference between this and a biosphere is simple, the biosphere is everything in general .

Biosphere

36

Extent of Earth's biosphere Every part of the planet, from the polar ice caps to the Equator, s life of some kind. Recent advances in microbiology have demonstrated that microbes live deep beneath the Earth's terrestrial surface, and that the total mass of microbial life in so-called "uninhabitable zones" may, in biomass, exceed all animal and plant life on the surface. The actual thickness of the biosphere on earth is difficult to measure. Birds typically fly at altitudes of 650 to 1,800 meters, and fish that live deep underwater can be found down to -8,372 meters in the Puerto Rico Trench.[2]

Water covers 71% of the Earth's surface. Image is the Earth photographed from Apollo 17.

There are more extreme examples for life on the planet: Rüppell's Vulture has been found at altitudes of 11,300 meters; Bar-headed Geese migrate at altitudes of at least 8,300 meters (over Mount Everest); Yaks live at elevations between 3,200 to 5,400 meters above sea level; mountain goats live up to 3,050 meters. Herbivorous animals at these elevations depend on

lichens, grasses, and herbs. Microscopic organisms live at such extremes that, taking them into consideration puts the thickness of the biosphere much greater. Culturable microbes have been found in the Earth's upper atmosphere as high as 41 km (25 mi) (Wainwright et al., 2003, in FEMS Microbiology Letters). It is unlikely, however, that microbes are active at such altitudes, where temperatures and air pressure are extremely low and ultraviolet radiation very high. More likely these microbes were brought into the upper atmosphere by winds or possibly volcanic eruptions. Barophilic marine microbes have been found at more than 10 km (6 mi) depth in the Marianas Trench (Takamia et al., 1997, in FEMS Microbiology Letters). Microbes are not limited to the air, water or the Earth's surface. Culturable thermophilic microbes have been extracted from cores drilled more than 5 km (3 mi) into the Earth's crust in Sweden (Gold, 1992, and Szewzyk, 1994, both in PNAS), from rocks between 65-75 °C. Temperature increases with increasing depth into the Earth's crust. The speed at which the temperature increases depends on many factors, including type of crust (continental vs. oceanic), rock type, geographic location, etc. The upper known limit of microbial is 122 °C (Methanopyrus kandleri Strain 116), and it is likely that the limit of life in the "deep biosphere" is defined by temperature rather than absolute depth. Our biosphere is divided into a number of biomes, inhabited by broadly similar flora and fauna. On land, biomes are separated primarily by latitude. Terrestrial biomes lying within the Arctic and Antarctic Circles are relatively barren of plant and animal life, while most of the more populous biomes lie near the equator. Terrestrial organisms in temperate and Arctic biomes have relatively small amounts of total biomass, smaller energy budgets, and display prominent adaptations to cold, including world-spanning migrations, social adaptations, homeothermy, estivation and multiple layers of insulation.

Biosphere

Specific biospheres When the word is followed by a number, it is usually referring to a specific system or number. Thus: • Biosphere 1, the planet Earth • Biosphere 2, a laboratory in Arizona which contains 3.15 acres (13,000 m²) of closed ecosystem. • BIOS-3, a closed ecosystem at the Institute of Biophysics in Krasnoyarsk, Siberia, in what was then the Soviet Union. • Biosphere J (CEEF, Closed Ecology Experiment Facilities), a experiment in Japan.[5] [6]

References [1] The Columbia Encyclopedia, Sixth Edition (http:/ / www. questia. com/ library/ encyclopedia/ biosphere. jsp). Columbia University Press. 2004. . Retrieved 2010-11-12. [2] Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life (http:/ / www. phschool. com/ el_marketing. html). Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. . [3] "Meaning of biosphere" (http:/ / www. webdictionary. co. uk/ definition. php?query=biosphere). WebDictionary.co.uk. WebDictionary.co.uk. . Retrieved 2010-11-12. [4] Seuss, E. (1875) Die Entstehung Der Alpen [The Origin of the Alps]. Vienna: W. Braunmuller. [5] Nakano et al.(1998)" Dynamic Simulation of Pressure Control System for the Closed Ecology Experiment Facility (http:/ / ci. nii. ac. jp/ naid/ 110002396764/ )", Transactions of the Japan Society of Mechanical Engineers. 64:107-114. [6] Institute for Environmental Sciences (http:/ / www. ies. or. jp/ index_e. html)

External links • Article on the Biosphere at Encyclopedia of Earth (http://www.eoearth.org/article/Biosphere) • GLOBIO.info (http://www.globio.info/), an ongoing programme to map the past, current and future impacts of human activities on the biosphere • Paul Crutzen Interview (http://www.vega.org.uk/video/programme/111) Freeview video of Paul Crutzen Nobel Laureate for his work on decomposition of ozone talking to Harry Kroto Nobel Laureate by the Vega Science Trust.

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Atmosphere

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Atmosphere An atmosphere (New Latin atmosphaera, created in the 17th century from Greek ἀτμός [atmos] "vapor"[1] and σφαῖρα [sphaira] "sphere"[2] ) is a layer of gases that may surround a material body of sufficient mass,[3] and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low. Some planets consist mainly of various gases, but only their outer layer is their atmosphere (see gas giants). The term stellar atmosphere describes the outer region of a star, and typically includes the portion starting from the opaque photosphere outwards. Relatively low-temperature stars may form compound molecules in their outer atmosphere. Earth's atmosphere, which contains oxygen used by most organisms for respiration and carbon dioxide used by plants, algae and cyanobacteria for photosynthesis, also protects living organisms from genetic damage by solar ultraviolet radiation. Its current composition is the product of billions of years of biochemical modification of the paleoatmosphere by living organisms.

View of Jupiter's active atmosphere, including the Great Red Spot.

Pressure Atmospheric pressure is the force of per unit area that is applied perpendicularly to a surface by the surrounding gas. It is determined by a planet's gravitational force in combination with the total mass of a column of air above a location. Units of air pressure are based on the internationally-recognized standard atmosphere (atm), which is defined as 101,325 Pa (or 1,013,250 dynes per cm²). The pressure of an atmospheric gas decreases with altitude due to the diminishing mass of gas above each location. The height at which the pressure from an atmosphere declines by a factor of e (an irrational number with a value of 2.71828..) is called the scale height and is denoted by H. For an atmosphere with a uniform temperature, the scale height is proportional to the temperature and inversely proportional to the mean molecular mass of dry air times the planet's gravitational acceleration. For such a model atmosphere, the pressure declines exponentially with increasing altitude. However, atmospheres are not uniform in temperature, so the exact determination of the atmospheric pressure at any particular altitude is more complex.

Escape Surface gravity, the force that holds down an atmosphere, differs significantly among the planets. For example, the large gravitational force of the giant planet Jupiter is able to retain light gases such as hydrogen and helium that escape from lower gravity objects. Second, the distance from the sun determines the energy available to heat atmospheric gas to the point where its molecules' thermal motion exceed the planet's escape velocity, the speed at which gas molecules overcome a planet's gravitational grasp. Thus, the distant and cold Titan, Triton, and Pluto are able to retain their atmospheres despite relatively low gravities. Interstellar planets, theoretically, may also retain thick atmospheres. Since a gas at any particular temperature will have molecules moving at a wide range of velocities, there will almost always be some slow leakage of gas into space. Lighter molecules move faster than heavier ones with the same thermal kinetic energy, and so gases of low molecular weight are lost more rapidly than those of high molecular weight. It is thought that Venus and Mars may have both lost much of their water when,

Atmosphere

39

after being photo dissociated into hydrogen and oxygen by solar ultraviolet, the hydrogen escaped. Earth's magnetic field helps to prevent this, as, normally, the solar wind would greatly enhance the escape of hydrogen. However, over the past 3 billion years the Earth may have lost gases through the magnetic polar regions due to auroral activity, including a net 2% of its atmospheric oxygen.[4] Other mechanisms that can cause atmosphere depletion are solar wind-induced sputtering, impact erosion, weathering, and sequestration — sometimes referred to as "freezing out" — into the regolith and polar caps.

Composition Initial atmospheric makeup is generally related to the chemistry and temperature of the local solar nebula during planetary formation and the subsequent escape of interior gases. These original atmospheres underwent much evolution over time, with the varying properties of each planet resulting in very different outcomes. The atmospheres of the planets Venus and Mars are primarily composed of carbon dioxide, with small quantities of nitrogen, argon, oxygen and traces of other gases. Atmospheric gases scatter blue light more than other wavelengths, giving the

The atmospheric composition on Earth is Earth a blue halo when seen from space. largely governed by the by-products of the very life that it sustains. Earth's atmosphere contains roughly (by molar content/volume) 78.09% nitrogen, 20.95% oxygen, a variable amount (average around 0.247%, National Center for Atmospheric Research) water vapor, 0.93% argon, 0.038% carbon dioxide, and traces of hydrogen, helium, and other "noble" gases. The low temperatures and higher gravity of the gas giants — Jupiter, Saturn, Uranus and Neptune — allows them to more readily retain gases with low molecular masses. These planets have hydrogen-helium atmospheres, with trace amounts of more complex compounds. Two satellites of the outer planets possess non-negligible atmospheres: Titan, a moon of Saturn, and Triton, a moon of Neptune, which are mainly nitrogen. Pluto, in the nearer part of its orbit, has an atmosphere of nitrogen and methane similar to Triton's, but these gases are frozen when farther from the Sun. Other bodies within the Solar System have extremely thin atmospheres not in equilibrium. These include the Moon (sodium gas), Mercury (sodium gas), Europa (oxygen), Io (sulfur), and Enceladus (water vapor). The atmospheric composition of an extra-solar planet was first determined using the Hubble Space Telescope. Planet HD 209458b is a gas giant with a close orbit around a star in the constellation Pegasus. The atmosphere is heated to temperatures over 1,000 K, and is steadily escaping into space. Hydrogen, oxygen, carbon and sulfur have been detected in the planet's inflated atmosphere.[5] and also there are fuels.

Atmosphere

Structure Earth The Earth's atmosphere consists, from the ground up, of the troposphere (which includes the planetary boundary layer or peplosphere as lowest layer), stratosphere (which includes the ozone layer), mesosphere, thermosphere (which contains the ionosphere), exosphere and also the magnetosphere. Each of the layers has a different lapse rate, defining the rate of change in temperature with height. Three quarters of the atmosphere lies within the troposphere, and the depth of this layer varies between 17 km at the equator and 7 km at the poles. The ozone layer, which absorbs ultraviolet energy from the Sun, is located primarily in the stratosphere, at altitudes of 15 to 35 km. The Kármán line, located within the thermosphere at an altitude of 100 km, is commonly used to define the boundary between the Earth's atmosphere and outer space. However, the exosphere can extend from 500 up to 10,000 km above the surface, where it interacts with the planet's magnetosphere.

Others Other astronomical bodies such as these listed have known atmospheres. In the Solar System • Atmosphere of Mercury • Atmosphere of Venus • Atmosphere of Earth • Atmosphere of the Moon • Atmosphere of Mars • Atmosphere of Jupiter • Atmosphere of Io • Atmosphere of Callisto • Atmosphere of Europa • Atmosphere of Ganymede • Atmosphere of Saturn • Atmosphere of Titan • Atmosphere of Enceladus • Atmosphere of Uranus • Atmosphere of Titania • Atmosphere of Neptune • Atmosphere of Triton • Atmosphere of Pluto Outside the Solar System • Atmosphere of HD 209458 b

Circulation The circulation of the atmosphere occurs due to thermal differences when convection becomes a more efficient transporter of heat than thermal radiation. On planets where the primary heat source is solar radiation, excess heat in the tropics is transported to higher latitudes. When a planet generates a significant amount of heat internally, such as is the case for Jupiter, convection in the atmosphere can transport thermal energy from the higher temperature

40

Atmosphere interior up to the surface.

Importance From the perspective of the planetary geologist, the atmosphere is an evolutionary agent essential to the morphology of a planet. The wind transports dust and other particles which erodes the relief and leaves deposits (eolian processes). Frost and precipitations, which depend on the composition, also influence the relief. Climate changes can influence a planet's geological history. Conversely, studying surface of earth leads to an understanding of the atmosphere and climate of a planet - both its present state and its past. For a meteorologist, the composition of the atmosphere determines the climate and its variations. For a biologist, the composition is closely dependent on the appearance of the life and its evolution.

See also • • • •

Atmometer (evaporimeter) Edge of space Ionosphere Sky

• Stellar atmosphere • Table of global climate system components

References [1] ἀτμός (http:/ / www. perseus. tufts. edu/ hopper/ text?doc=Perseus:text:1999. 04. 0057:entry=a)tmo/ s), Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library [2] σφαῖρα (http:/ / www. perseus. tufts. edu/ hopper/ text?doc=Perseus:text:1999. 04. 0057:entry=sfai=ra^), Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library [3] Ontario Science Centre website (http:/ / www. ontariosciencecentre. ca/ school/ clc/ visits/ glossary. asp) [4] Seki, K.; Elphic, R. C.; Hirahara, M.; Terasawa, T.; Mukai, T. (2001). "On Atmospheric Loss of Oxygen Ions from Earth Through Magnetospheric Processes" (http:/ / www. sciencemag. org/ cgi/ content/ full/ 291/ 5510/ 1939). Science 291 (5510): 1939–1941. doi:10.1126/science.1058913. PMID 11239148. . Retrieved 2007-03-07. [5] Weaver, D.; Villard, R. (2007-01-31). "Hubble Probes Layer-cake Structure of Alien World's Atmosphere" (http:/ / hubblesite. org/ newscenter/ archive/ releases/ 2007/ 07/ ). Hubble News Center. . Retrieved 2007-03-11.

External links • Properties of atmospheric strata - The flight environment of the atmosphere (http://www.allstar.fiu.edu/aero/ fltenv2.htm) • Atmosphere (http://www.mdpi.com/journal/atmosphere/) - an Open Access journal

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Lithosphere

Lithosphere The lithosphere (pronounced /ˈlɪθəsfɪər/, from the Greek λίθος [lithos] for "rocky" + σφαῖρα [sphaira] for "sphere") is the rigid[1] outermost shell of a rocky planet. It comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.

Earth's lithosphere In the Earth, the lithosphere includes The tectonic plates of the lithosphere on Earth the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is underlain by the asthenosphere, the weaker, hotter, and deeper part of the upper mantle. The boundary between the lithosphere and the underlying asthenosphere is defined by a difference in response to stress: the lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere deforms viscously and accommodates strain through plastic deformation. The lithosphere is broken into tectonic plates. The uppermost Earth cutaway from core to exosphere part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the soil forming process is called the pedosphere. The concept of the lithosphere as Earth’s strong outer layer was developed by Joseph Barrell, who wrote a series of papers introducing the concept.[2] [3] [4] The concept was based on the presence of significant gravity anomalies over continental crust, from which he inferred that there must exist a strong upper layer (which he called the lithosphere) above a weaker layer which could flow (which he called the asthenosphere). These ideas were expanded by Daly (1940)[5] , and have been broadly accepted by geologists and geophysicists. Although these ideas about lithosphere and asthenosphere were developed long before plate tectonic theory was articulated in the 1960s, the concepts that a strong lithosphere exists and that this rests on a weak asthenosphere are essential to that theory. The lithosphere provides a conductive lid atop the convecting mantle; as such, it affects heat transport through the Earth. There are two types of lithosphere: • Oceanic lithosphere, which is associated with Oceanic crust and exists in the ocean basins

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Lithosphere

43

• Continental lithosphere, which is associated with Continental crust The thickness of the lithosphere is considered to be the depth to the isotherm associated with the transition between brittle and viscous behavior[6] . The temperature at which olivine begins to deform viscously (~1000°C) is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle. Oceanic lithosphere is typically about 50–100 km thick (but beneath the mid-ocean ridges is no thicker than the crust), while continental lithosphere has a range in thickness from about 40 km to perhaps 200 km; the upper ~30 to ~50 km of typical continental lithosphere is crust. The mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity.

Oceanic Lithosphere Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle (peridotite) and is denser than continental lithosphere, for which the mantle is associated with crust made of felsic rocks. Oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle, and causes the oceanic lithosphere to become increasingly thick and dense with age. The thickness of the mantle part of the oceanic lithosphere can be approximated as a thermal boundary layer that thickens as the square root of time.

Here, and

is the thickness of the oceanic mantle lithosphere,

is the thermal diffusivity (approximately 10−6 m2/s),

is time.

Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years, but after this becomes increasingly denser than asthenosphere. This is because the chemically-differentiated oceanic crust is lighter than asthenosphere, but due to thermal contraction, the mantle lithosphere is more dense than the asthenosphere. The gravitational instability of mature oceanic lithosphere has the effect that at subduction zones, oceanic lithosphere invariably sinks underneath the overriding lithosphere, which can be oceanic or continental. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones. As a result, oceanic lithosphere is much younger than continental lithosphere: the oldest oceanic lithosphere is about 170 million years old, while parts of the continental lithosphere are billions of years old. The oldest parts of continental lithosphere underlie cratons, and the mantle lithosphere there is thicker and less dense than typical; the relatively low density of such mantle "roots of cratons" helps to stabilize these regions.[7] [8]

Subducted lithosphere Geophysical studies in the early 21st Century posit that large pieces of the lithosphere have been subducted into the mantle as deep as 2900 km to near the core-mantle boundary[9] , while others "float" in the upper mantle,[10] [11] while some stick down into the mantle as far as 400 km but remain "attached" to the continental plate above,[12] similar to the extent of the "tectosphere" proposed by Jordan in 1988.[13]

Mantle xenoliths Geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths[14] brought up in kimberlite, lamproite, and other volcanic pipes. The histories of these xenoliths have been investigated by many methods, including analyses of abundances of isotopes of osmium and rhenium. Such studies have confirmed that mantle lithospheres below some cratons have persisted for periods in excess of 3 billion years, despite the mantle flow that accompanies plate tectonics.[15]

Lithosphere

References Footnotes [1] [2] [3] [4] [5] [6] [7] [8]

Skinner, B.J. & Porter, S.C.: Physical Geology, page 17, chapt. The Earth: Inside and Out, 1987, John Wiley & Sons, ISBN 0-471-05668-5 Barrell, J. 1914 The strength of the Earth's crust. Journal of Geology.22, 425-433. Barrell, J. 1914 The strength of the Earth's crust. Journal of Geology 22, 441-468. Barrell, J. 1914 The strength of the Earth's crust. Journal of Geology 22, 655-683. Daly, R. 1940 Strength and structure of the Earth. New York: Prentice-Hall. Parsons, B. and McKenzie, D. 1978. Mantle Convection and the thermal structure of the plates. Journal of Geophysical Research. Jordan, T. H. 1978 Composition and development of the continental tectosphere. Nature 274, 544-548. O’Reilly, Suzanne Y. et al. (2009) "Ultradeep continental roots and their oceanic remnants: A solution to the geochemical “mantle reservoir” problem?" LITHOS doi: 10.1016/j.lithos.2009.04.028 [9] Burke, K. and Torsvik, T. H. (2004) "Derivation of Large Igneous Provinces of the past 200 million years from long-term heterogeneities in the deep mantle Earth and Planetary Science Letters 227: pp. 531-538 [10] Replumaz, A. et al. (2004) "4-D evolution of SE Asia's mantle from geological reconstructions and seismic tomography" Earth and Planetary Science Letters 221: pp. 103-115, doi:10.1016/S0012-821X(04)00070-6 [11] Li, Chang et al. (2008) "A new global model for P wave speed variations in Earth's mantle" Geochemistry Geophysics Geosystems 9(5): Q05018, doi: 10.1029/2007GC001806 [12] O’Reilly, Suzanne Y. et al. (2009) "Ultradeep continental roots and their oceanic remnants: A solution to the geochemical “mantle reservoir” problem" Lithos doi:10.1016/j.lithos.2009.04.028 [13] Jordan, T.H. (1988) "Structure and formation of the continental tectosphere" Journal of Petrology 29(Special Lithosphere Issue): pp. 11-38 [14] Nixon, P.H. (1987) Mantle xenoliths : J. Wiley & Sons, 844 p. (ISBN 0-471-91209-3) [15] Carlson, R. W., Pearson, D. G., and James, D. E., 2004, Physical, chemical, and chronological characteristics of continental mantle. Reviews of Geophysics 43, 8755-1209/05/2004RG000156.

Notations • Stanley Chernicoff and Donna Whitney. Geology. An Introduction to Physical Geology, 4th ed., Pearson 1990

External links • Earth's Crust, Lithosphere and Asthenosphere (http://www.windows.ucar.edu/cgi-bin/tour_def/earth/interior/ earths_crust.html) • Crust and Lithosphere (http://www.geolsoc.org.uk/template.cfm?name=lithosphere)

See also • • • • • • • •

Biosphere Cryosphere Earth's atmosphere Hydrosphere Kola Superdeep Borehole Pedosphere Plate tectonics Table of global climate system components

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Geosphere

Geosphere The term geosphere is often used to refer to the densest parts of Earth, which consist mostly of rock and regolith.[1] The Geosphere is the parts on the inside of the earth, planets, or other bodies. In Aristotelian physics, the term was applied to four spherical natural places, concentrically nested around the center of the Earth, as described in the lectures Physica and Meteorologica. They were believed to explain the motions of the four terrestrial elements: Earth, Water, Air and Fire. In modern texts, geosphere refers to the solid parts of the Earth and is used along with atmosphere, hydrosphere, and biosphere to describe the systems of the Earth. In that context, sometimes the term "lithosphere" is used instead of geosphere. However, the lithosphere only refers to the uppermost layers of the solid Earth (oceanic and continental crustal rocks and uppermost mantle).[2] Since space exploration began, it has been observed that the extent of the ionosphere or plasmasphere is highly variable, and often much larger than previously appreciated, at times extending to the boundaries of the Earth's magnetosphere or geomagnetosphere.[3] This highly variable outer boundary of geogenic matter has been referred to as the "geopause",[4] to suggest the relative scarcity of such matter beyond it, where the solar wind dominates.

Notes [1] Skinner, B: "The Dynamic Earth.", page 21. John Wiley & Sons, Inc, 2000 ISBN 0-471-16118-7 [2] Allaby,A. and Allaby, M. (eds). 2003. The Dictionary of Earth Sciences. Oxford University Press. Oxford University Press Inc., New York. 2nd edition. pg. 320. [3] Siscoe, G.: Aristotle on the Magnetosphere, Eos Transactions of Am. Geophys. Un., v.72, pp. 69-70, 1991. [4] Moore, T.E. and D.C. Delcourt, The Geopause, Revs. Geophys., v32(2), p.175, 1995.

Pedosphere The pedosphere (from the Greek πέδον [pedon] soil, earth + σφαίρα [sfaíra] sphere) is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere.[1] The pedosphere acts as the mediator of chemical and biogeochemical flux into and out of these respective systems and is made up of gaseous, mineralic, fluid and biologic components. The pedosphere lies within the Critical Zone, a broader interface that includes vegetation, pedosphere, groundwater aquifer systems, regolith and finally ends at some depth in the bedrock where the biosphere and hydrosphere cease to make significant changes to the chemistry at depth. As part of the larger global system, any particular environment in which soil forms is influenced solely by its geographic position on the globe as climatic, geologic, biologic and anthropogenic changes occur with changes in longitude and latitude. The pedosphere lies below the vegetative cover of the biosphere and above the hydrosphere and lithosphere. The soil forming process (pedogenesis) can begin without the aid of biology but is significantly quickened in the presence of biologic reactions. Soil formation begins with the chemical and/or physical breakdown of minerals to form the initial material that overlies the bedrock substrate. Biology quickens this by secreting acidic compounds (dominantly fulvic acids) that help break rock apart. Particular biologic pioneers are lichen, mosses and seed bearing plants[2] but many other inorganic reactions take place that diversify the chemical makeup of the early soil layer. Once weathering and decomposition products accumulate, a coherent soil body allows the migration of fluids both vertically and laterally through the soil profile causing ion exchange between solid, fluid and gaseous phases. As time progresses, the bulk geochemistry of the soil layer will deviate away from the initial composition of the bedrock and will evolve to a chemistry that reflects the type of reactions that take place in the soil.[3]

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Pedosphere

Lithosphere The primary conditions for soil development are controlled by the chemical composition of the rock that the soil will eventually be forming on. Rock types that form the base of the soil profile are often either sedimentary (carbonate or siliceous), igneous or metaigneous (metamorphosed igneous rocks) or volcanic and metavolcanic rocks. The rock type and the processes that lead to its exposure at the surface are controlled by the regional geologic setting of the specific area under study, which revolve around the underlying theory of plate tectonics, subsequent deformation, uplift, subsidence and deposition. Metaigneous and metavolcanic rocks form the largest component of cratons and are high in silica. Igneous and volcanic rocks are also high in silica but with non-metamorphosed rock, weathering becomes faster and the mobilization of ions is more widespread. Rocks high in silica produce silicic acid as a weathering product. There are few rock types that lead to localized enrichment of some of the biologically limiting elements like phosphorus (P) and nitrogen (N). Phosphatic shale (<15% P2O5) and phosphorite (>15% P2O5) form in anoxic deep water basins that preserve organic material.[4] Greenstone (metabasalt), phyllite and schist release up to 30-50% of the nitrogen pool.[5] Thick successions of carbonate rocks are often deposited on craton margins during sea level rise. The widespread dissolution of carbonate and evaporate minerals leads to elevated levels of Mg2+, HCO3-, Sr2+, Na+, Cland SO42- ions in aqueous solution.[6]

Weathering and dissolution of minerals The process of soil formation is dominated by chemical weathering of silicate minerals, aided by acidic products of pioneering plants and organisms as well as carbonic acid inputs from the atmosphere. Carbonic acid is produced in the atmosphere and soil layers through the carbonation reaction. H2O + CO2 → H++ HCO3- → H2CO3[3] This is the dominant form of chemical weathering and aides in the breakdown of carbonate minerals like calcite and dolomite and silicate minerals like feldspar. The breakdown of the Na-feldspar, albite, by carbonic acid to form kaolinite clay is as follows: 2NaAlSi3O8 + 2H2CO3 + 9H2O → 2Na+ + 2HCO3- + 4H4SiO4 + Al2Si2O5(OH)4[3]

Evidence of this reaction in the field would be elevated levels of bicarbonate (HCO3-), sodium and silica ions in the water runoff. The breakdown of carbonate minerals: CaCO3 + H2CO3 → Ca2+ + 2HCO3-[3] or CaCO3 → Ca2+ + CO32-[6] The further dissolution of carbonic acid (H2CO3) and bicarbonate (HCO3) produces CO2 gas. Oxidization is also a major contributor to the breakdown of many silicate minerals and formation of secondary minerals (diagenesis) in the early soil profile. Oxidation of Olivine (FeMgSiO2) releases Fe, Mg and Si ions.[7] The Mg is soluble in water and is carried in the runoff but the Fe often reacts with oxygen to precipitate Fe2O3 (hematite), the oxidized state of iron oxide. Sulfur, a byproduct of decaying organic material will also react to Fe to form pyrite (FeS2) but often in reducing environments. Pyrite dissolution leads to high pH levels due to elevated H+ ions and further precipitation of Fe2O3[3] ultimately changing the redox conditions of the environment.

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Pedosphere

Biosphere Inputs from the biosphere may begin with lichen and other microorganisms that secrete oxalic acid. These microorganisms, associated with the lichen community or independently inhabiting rocks, include a number of blue-green algae, green algae, various fungi, and numerous bacteria.[8] Lichen has long been viewed as the pioneers of soil development as the following statement suggests: “The initial conversion of rock into soil is carried on by the pioneer lichens and their successors, the mosses, in which the hair-like rhizoids assume the role of roots in breaking down the surface into fine dust[9] ” However, lichens are not necessarily the only pioneering organisms nor the earliest form of soil formation as it has been documented that seed-bearing plants may occupy an area and colonize quicker than lichen. Also, eolian sedimentation can produce high rates of sediment accumulation. Nonetheless, lichen can certainly withstand harsher conditions than most vascular plants and although they have slower colonization rates, do form the dominant group in alpine regions. Acids released from plant roots include acetic and citric acids. During the decay of organic matter Phenolic acids are released from plant matter and humic and fulvic acids are released by soil microbes. These organic acids speed up chemical weathering by combining with some of the weathering products in a process known as chelation. In the soil profile, the organic acids are often concentrated at the top while carbonic acid plays a larger role towards the bottom or below in the aquifer.[3] As the soil column develops further into thicker accumulations, larger animals come to inhabit the soil and continue to alter the chemical evolution of their respective niche. Earthworms aerate the soil and convert large amounts of organic matter into rich humus, improving soil fertility. Small burrowing mammals store food, grow young and may hibernate in the pedosphere altering the course of soil evolution. Large mammalian herbivores above ground transport nutrients in form of nitrogen-rich waste and phosphorus-rich antlers while predators leave phosphorus-rich piles of bones on the soil surface, leading the localized enrichment of the soil below.

Redox conditions in wetland soils Nutrient cycling in lakes and freshwater wetlands depends heavily on redox conditions.[3] Under a few millimeters of water heterotrophic bacteria metabolize and consume oxygen. They therefore deplete the soil of oxygen and create the need for anaerobic respiration. Some anaerobic microbial processes include denitrification, sulfate reduction and methanogenesis and are responsible for the release of N2 (nitrogen), H2S (hydrogen sulfide) and CH4 (methane). Other anaerobic microbial processes are linked to changes in the oxidation state of iron and manganese. As a result of anaerobic decomposition, the soil stores large amounts of organic carbon because decomposition is incomplete.[3] The redox potential describes which way chemical reactions will proceed in oxygen deficient soils and controls the nutrient cycling in flooded systems. Redox potential, or reduction potential, is used to express the likelihood of an environment to receive electrons[3] and therefore become reduced. For example, if a system already has plenty of electrons (anoxic, organic-rich shale) it is reduced and will likely donate electrons to a part of the system that has a low concentration of electrons, or an oxidized environment, to equilibrate to the chemical gradient. The oxidized environment has high redox potential, whereas the reduced environment has a low redox potential. The redox potential is controlled by the oxidation state of the chemical species, pH and the amount of oxygen (O2) there is in the system. The oxidizing environment accepts electrons because of the presence of O2, which acts as electron acceptors: O2 + 4e- + 4H+ → H2O[3] This equation will tend to move to the right in acidic conditions which causes higher redox potentials to be found at lower pH levels. Bacteria, heterotrophic organisms, consume oxygen while decomposing organic material which depletes the soils of oxygen, thus increasing the redox potential. In low redox conditions the deposition of ferrous iron (Fe2+) will increase with decreasing decomposition rates, thus preserving organic remains and depositing

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Pedosphere humus. At high redox potential, the oxidized form of iron, ferric iron (Fe3+), will be deposited commonly as hematite. By using analytical geochemical tools such as x-ray fluorescence (XRF) or inductively coupled mass spectroscopy (I-MS) the two forms of Fe (Fe2+ and Fe3+) can be measured in ancient rocks therefore determining the redox potential for ancient soils. Such a study was done on Permian through Triassic rocks (300-200 million years old) in Japan and British Colombia. The geologists found hematite throughout the early and middle Permian but began to find the reduced form of iron in pyrite within the ancient soils near the end of the Permian and into the Triassic. This suggests that conditions became less oxygen rich, even anoxic, during the late Permian which eventually lead to the greatest extinction in earth’s history, the P-T extinction.[10] Decomposition in anoxic or reduced soils is also carried out by sulfur-reducing bacteria which, instead of O2 use SO42- as an electron acceptor and produce hydrogen sulfide (H2S) and carbon dioxide in the process: 2H+ + SO42- + 2(CH2O) → 2CO2 + H2S +2H2O[3] The H2S gas percolates upwards and reacts with Fe2+ and precipitates pyrite, acting as a trap for the toxic H2S gas. However, H2S is still a large fraction of emissions from wetland soils.[11] In most freshwater wetlands there is little sulfate (SO42-) so methanogenesis becomes the dominant form of decomposition by methanogenic bacteria only when sulfate is depleted. Acetate, a compound that is a byproduct of fermenting cellulose is split by methanogenic bacteria to produce methane (CH4) and carbon dioxide (CO2), which are released to the atmosphere. Methane is also released during the reduction of CO2 by the same bacteria.[3]

Atmosphere In the pedosphere it is safe to assume that gases are in equilibrium with the atmosphere.[6] Because plant roots and soil microbes release CO2 to the soil, the concentration of bicarbonate(HCO3) in soil waters is much greater than that in equilibrium with the atmosphere,[12] the high concentration of CO2 and the occurrence of metals in soil solutions results in lower pH levels in the soil. Gases that escape from the pedosphere to the atmosphere include the gaseous byproducts of carbonate dissolution, decomposition, redox reactions and microbial photosynthesis. The main inputs from the atmosphere are aeolian sedimentation, rainfall and gas diffusion. Eolian sedimentation includes anything that can be entrained by wind or that stays suspended, seemingly indefinitely, in air and includes a wide variety of aerosol particles, biological particles like pollen and dust to pure quartz sand. Nitrogen is the most abundant constituent in rain, as water vapor utilizes aerosol particles to nucleate rain droplets.[3]

Soil in Forests Soil is well developed in the forest as suggested by the thick humus layers, rich diversity of large trees and animals that live there. In forests, precipitation exceeds evapotranspiration which results in an excess of water that percolates downward through the soil layers. Slow rates of decomposition leads to large amounts of fulvic acid, greatly enhancing chemical weathering. The downward percolation, in conjunction with chemical weathering leaches magnesium (Mg), iron (Fe), and aluminum (Al) from the soil and transports them downward, a process known as podzolization. This process leads to marked contrasts in the appearance and chemistry of the soil layers.[3]

Soil in the Tropics Tropical forests (rainforests) receive more insolation and rainfall over longer growing seasons than any other environment on earth. With these elevated temperatures, insolation and rainfall, biomass is extremely productive leading to carbon production as much as 800gCm2-yr-.[3] Higher temperatures and larger amounts of water contribute to higher rates of chemical weathering. Increased rates of decomposition cause smaller amounts of fulvic acid to percolate and leach metals from the zone of active weathering. Thus, in stark contrast to soil in forests, tropical forests have little to no podzolization and therefore do not have marked visual and chemical contrasts with the soil

48

Pedosphere layers. Instead, the mobile metals Mg, Fe and Al are precipitated as oxide minerals giving the soil a rusty red color.[3]

Soil in Grasslands and Deserts Precipitation in grasslands is equal to or less than evapotranspiration and causes soil development to operate in relative drought.[3] Leaching and migration of weathering products is therefore decreased. Large amounts of evaporation causes buildup of calcium (Ca) and other large cations flocculate clay minerals and fulvic acids in the upper soil profile. Impermeable clay limits downward percolation of water and fulvic acids, reducing chemical weathering and podzolization. The depth to the maximum concentration of clay increases in areas of increased precipitation and leaching. When leaching is decreased, the Ca precipitates as calcite (CaCO3) in the lower soil levels, a layer known as caliche. Deserts behave similarly to grasslands but operate in constant drought as precipitation is less than evapotranspiration. Chemical weathering proceeds more slowly than in grasslands and beneath the caliche layer may be a layer of gypsum and halite.[3] To study soils in deserts, pedologists have used the concept of chronosequences to relate timing and development of the soil layers. It has been shown that P is leached very quickly from the system and therefore decreases with increasing age.[13] Furthermore, carbon buildup in the soils is decreased due to slower decomposition rates. As a result, the rates of carbon circulation in the biogeochemical cycle is decreased.

See also • • • • • • • • • • • • •

Planetary habitability Biodiversity Bioregion Earth Science Ecology Ecosystem Natural environment Biogeochemistry Biogeochemical cycle Geochemistry Soil Science Geology Chemistry

References [1] [2] [3] [4] [5] [6] [7]

Elissa Levine, 2001, The Pedosphere As A Hub (http:/ / soil. gsfc. nasa. gov/ ped/ pedosph. htm) Cooper, R., 1953, The role of lichens in soil formation and plant succession: Ecology, v. 34, no. 4, p. 805-807. Schlesinger, W., An analysis of global change: Biogeochemistry, Academic Press. Boggs, S., Jr., 1995, Principles of Sedimentary and Stratigraphy. Prentice Hall, NJ, USA Holloway, J., and Dahlgren, R., 1999, Geologic nitrogen in terrestrial biogeochemical cycling: Geology, v. 27, no. 6, p. 567. Faure, G., 1998, Principles and Applications of Geochemistry, 600 pp, Prentice-Hall, Upper Saddle River, NJ. Grandstaff, D., 1986, The dissolution rate of forsteritic olivine from Hawaiian beach sand: Rates of chemical weathering of rocks and minerals, p. 41–59. [8] Chen, J., Blume, H., and Beyer, L., 2000, Weathering of rocks induced by lichen colonization--a review: Catena, v. 39, no. 2, p. 121-146. [9] Clements, F.E., and Shelford, V.E., 1939, Bioecology. John Wiley, New York. [10] Isozaki, Y., 1997, Permo-Triassic boundary superanoxia and stratified superocean: records from lost deep sea: Science, v. 276, no. 5310, p. 235. [11] Kelly, D., and Smith, N., 1990, Organic sulfur compounds in the environment: biogeochemistry, microbiology, and ecological aspects: Advances in microbial ecology, v. 11, p. 345-385.

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Pedosphere [12] Piñol, J., Alcañiz, J., and Rodà, F., 1995, Carbon dioxide efflux and pCO2 in soils of three Quercusilex montane forests: Biogeochemistry, v. 30, no. 3, p. 191-215. [13] Lajtha, K., and Schlesinger, W., 1988, The biogeochemistry of phosphorus cycling and phosphorus availability along a desert soil chronosequence: Ecology, v. 69, no. 1, p. 24-39.

Cryosphere The cryosphere (from the Ancient Greek word "κρύος" [cryos meaning "cold", "frost" or "ice"]) is the term which collectively describes the portions of the Earth’s surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground (which includes permafrost). Overview of the Cryosphere and its larger components, from the UN Environment Thus there is a wide overlap with the [1] Programme Global Outlook for Ice and Snow . hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and s generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation. Through these processes, the cryosphere plays a significant role in global climate and in climate model response to global change.

Structure Frozen water is found on the Earth’s surface primarily as snow cover, freshwater ice in lakes and rivers, sea ice, glaciers, ice sheets, and frozen ground and permafrost (permanently-frozen ground). The residence time of water in each of these cryospheric sub-systems varies widely. Snow cover and freshwater ice are essentially seasonal, and most sea ice, except for ice in the central Arctic, lasts only a few years if it is not seasonal. A given water particle in glaciers, ice sheets, or ground ice, however, may remain frozen for 10-100,000 years or longer, and deep ice in parts of East Antarctica may have an age approaching 1 million years. Most of the world’s ice volume is in Antarctica, principally in the East Antarctic Ice Sheet. In of areal extent, however, Northern Hemisphere winter snow and ice extent comprise the largest area, amounting to an average 23% of hemispheric surface area in January. The large areal extent and the important climatic roles of snow and ice, related to their unique physical properties, indicate that the ability to observe and model snow and ice-cover extent, thickness, and physical properties (radiative and thermal properties) is of particular significance for climate research. There are several fundamental physical properties of snow and ice that modulate energy exchanges between the surface and the atmosphere. The most important properties are the surface reflectance (albedo), the ability to transfer heat (thermal diffusivity), and the ability to change state (latent heat). These physical properties, together with surface roughness, emissivity, and dielectric characteristics, have important implications for observing snow and ice from space. For example, surface roughness is often the dominant factor determining the strength of radar backscatter .[2] Physical properties such as crystal structure, density, length, and liquid-water content are important factors affecting the transfers of heat and water and the scattering of microwave energy. The surface reflectance of incoming solar radiation is important for the surface energy balance (SEB). It is the ratio of reflected to incident solar radiation, commonly referred to as albedo. Climatologists are primarily interested in albedo integrated over the shortwave portion of the electromagnetic spectrum (~0.3 to 3.5 nm), which coincides with the main solar energy input. Typically, albedo values for non-melting snow-covered surfaces are high (~80-90%)

50

Cryosphere except in the case of forests. The higher albedos for snow and ice cause rapid shifts in surface reflectivity in autumn and spring in high latitudes, but the overall climatic significance of this increase is spatially and temporally modulated by cloud cover. (Planetary albedo is determined principally by cloud cover, and by the small amount of total solar radiation received in high latitudes during winter months.) Summer and autumn are times of high-average cloudiness over the Arctic Ocean so the albedo associated with the large seasonal changes in sea-ice extent is greatly reduced. Groisman et al. (1994a) observed that snow cover exhibited the greatest influence on the Earth radiative balance in the spring (April to May) period when incoming solar radiation was greatest over snow-covered areas.[3] The thermal properties of cryospheric elements also have important climatic consequences. Snow and ice have much lower thermal diffusivities than air. Thermal diffusivity is a measure of the speed at which temperature waves can penetrate a substance. Snow and ice are many orders of magnitude less efficient at diffusing heat than air. Snow cover insulates the ground surface, and sea ice insulates the underlying ocean, decoupling the surface-atmosphere interface with respect to both heat and moisture fluxes. The flux of moisture from a water surface is eliminated by even a thin skin of ice, whereas the flux of heat through thin ice continues to be substantial until it attains a thickness in excess of 30 to 40 cm. However, even a small amount of snow on top of the ice will dramatically reduce the heat flux and slow down the rate of ice growth. The insulating effect of snow also has major implications for the hydrological cycle. In non-permafrost regions, the insulating effect of snow is such that only near-surface ground freezes and deep-water drainage is uninterrupted.[4] While snow and ice act to insulate the surface from large energy losses in winter, they also act to retard warming in the spring and summer because of the large amount of energy required to melt ice (the latent heat of fusion, 3.34 x 105 J/kg at 0°C). However, the strong static stability of the atmosphere over areas of extensive snow or ice tends to confine the immediate cooling effect to a relatively shallow layer, so that associated atmospheric anomalies are usually short-lived and local to regional in scale.[5] In some areas of the world such as Eurasia, however, the cooling associated with a heavy snowpack and moist spring soils is known to play a role in modulating the summer monsoon circulation.[6] Gutzler and Preston (1997) recently presented evidence for a similar snow-summer circulation over the southwestern United States.[7] The role of snow cover in modulating the monsoon is just one example of a short-term cryosphere-climate involving the land surface and the atmosphere. From Figure 1 it can be seen that there are numerous cryosphere-climate s in the global climate system. These operate over a wide range of spatial and temporal scales from local seasonal cooling of air temperatures to hemispheric-scale variations in ice sheets over time-scales of thousands of years. The mechanisms involved are often complex and incompletely understood. For example, Curry et al. (1995) showed that the so-called “simple” sea ice-albedo involved complex interactions with lead fraction, melt ponds, ice thickness, snow cover, and sea-ice extent.

Snow Snow cover has the second-largest areal extent of any component of the cryosphere, with a mean maximum areal extent of approximately 47 million km². Most of the Earth’s snow-covered area (SCA) is located in the Northern Hemisphere, and temporal variability is dominated by the seasonal cycle; Northern Hemisphere snow-cover extent ranges from 46.5 million km² in January to 3.8 million km² in August.[8] North American winter SCA has exhibited an increasing trend over much of this century (Brown and Goodison 1996; Hughes et al. 1996) largely in response to an increase in precipitation.[9] However, the available satellite data show that the hemispheric winter snow cover has exhibited little interannual variability over the 1972-1996 period, with a coefficient of variation (COV=s.d./mean) for January Northern Hemisphere snow cover of < 0.04. According to Groisman et al. (1994a) Northern Hemisphere spring snow cover should exhibit a decreasing trend to explain an observed increase in Northern Hemisphere spring air temperatures this century. Preliminary estimates of SCA from historical and reconstructed in situ snow-cover data suggest this is the case for Eurasia, but not for North America, where spring snow cover has remained close to

51

Cryosphere current levels over most of this century.[10] Because of the close relationship observed between hemispheric air temperature and snow-cover extent over the period of satellite data (IPCC 1996), there is considerable interest in monitoring Northern Hemisphere snow-cover extent for detecting and monitoring climate change. Snow cover is an extremely important storage component in the water balance, especially seasonal snowpacks in mountainous areas of the world. Though limited in extent, seasonal snowpacks in the Earth’s mountain ranges for the major source of the runoff for stream flow and groundwater recharge over wide areas of the midlatitudes. For example, over 85% of the annual runoff from the Colorado River basin originates as snowmelt. Snowmelt runoff from the Earth’s mountains fills the rivers and recharges the aquifers that over a billion people depend on for their water resources. Further, over 40% of the world’s protected areas are in mountains, attesting to their value both as unique ecosystems needing protection and as recreation areas for humans. Climate warming is expected to result in major changes to the partitioning of snow and rainfall, and to the timing of snowmelt, which will have important implications for water use and management. These changes also involve potentially important decadal and longer time-scale s to the climate system through temporal and spatial changes in soil moisture and runoff to the oceans.(Walsh 1995). Freshwater fluxes from the snow cover into the marine environment may be important, as the total flux is probably of the same magnitude as desalinated ridging and rubble areas of sea ice.[11] In addition, there is an associated pulse of precipitated pollutants which accumulate over the Arctic winter in snowfall and are released into the ocean upon ablation of the sea-ice .

Sea ice Sea ice covers much of the polar oceans and forms by freezing of sea water. Satellite data since the early 1970s reveal considerable seasonal, regional, and interannual variability in the sea-ice covers of both hemispheres. Seasonally, sea-ice extent in the Southern Hemisphere varies by a factor of 5, from a minimum of 3-4 million km² in February to a maximum of 17-20 million km² in September.[12] [13] The seasonal variation is much less in the Northern Hemisphere where the confined nature and high latitudes of the Arctic Ocean result in a much larger perennial ice cover, and the surrounding land limits the equatorward extent of wintertime ice. Thus, the seasonal variability in Northern Hemisphere ice extent varies by only a factor of 2, from a minimum of 7-9 million km² in September to a maximum of 14-16 million km² in March.[13] [14] The ice cover exhibits much greater regional-scale interannual variability than it does hemispherical. For instance, in the region of the Seas of Okhotsk and Japan, maximum ice extent decreased from 1.3 million km² in 1983 to 0.85 million km² in 1984, a decrease of 35%, before rebounding the following year to 1.2 million km² .[13] The regional fluctuations in both hemispheres are such that for any several-year period of the satellite record some regions exhibit decreasing ice coverage while others exhibit increasing ice cover.[15] The overall trend indicated in the ive microwave record from 1978 through mid-1995 shows that the extent of Arctic sea ice is decreasing 2.7% per decade.[16] Subsequent work with the satellite ive-microwave data indicates that from late October 1978 through the end of 1996 the extent of Arctic sea ice decreased by 2.9% per decade while the extent of Antarctic sea ice increased by 1.3% per decade.[17]

Lake ice and river ice Ice forms on rivers and lakes in response to seasonal cooling. The sizes of the ice bodies involved are too small to exert other than localized climatic effects. However, the freeze-up/break-up processes respond to large-scale and local weather factors, such that considerable interannual variability exists in the dates of appearance and disappearance of the ice. Long series of lake-ice observations can serve as a proxy climate record, and the monitoring of freeze-up and break-up trends may provide a convenient integrated and seasonally specific index of climatic perturbations. Information on river-ice conditions is less useful as a climatic proxy because ice formation is strongly dependent on river-flow regime, which is affected by precipitation, snow melt, and watershed runoff as well as being subject to human interference that directly modifies channel flow, or that indirectly affects the runoff via

52

Cryosphere land-use practices. Lake freeze-up depends on the heat storage in the lake and therefore on its depth, the rate and temperature of any inflow, and water-air energy fluxes. Information on lake depth is often unavailable, although some indication of the depth of shallow lakes in the Arctic can be obtained from airborne radar imagery during late winter (Sellman et al. 1975) and spaceborne optical imagery during summer (Duguay and Lafleur 1997). The timing of breakup is modified by snow depth on the ice as well as by ice thickness and freshwater inflow.

Frozen ground and permafrost Frozen ground (permafrost and seasonally frozen ground) occupies approximately 54 million km² of the exposed land areas of the Northern Hemisphere (Zhang et al., 2003) and therefore has the largest areal extent of any component of the cryosphere. Permafrost (perennially frozen ground) may occur where mean annual air temperatures (MAAT) are less than -1 or -2°C and is generally continuous where MAAT are less than -7°C. In addition, its extent and thickness are affected by ground moisture content, vegetation cover, winter snow depth, and aspect. The global extent of permafrost is still not completely known, but it underlies approximately 20% of Northern Hemisphere land areas. Thicknesses exceed 600 m along the Arctic coast of northeastern Siberia and Alaska, but, toward the margins, permafrost becomes thinner and horizontally discontinuous. The marginal zones will be more immediately subject to any melting caused by a warming trend. Most of the presently existing permafrost formed during previous colder conditions and is therefore relic. However, permafrost may form under present-day polar climates where glaciers retreat or land emergence exposes unfrozen ground. Washburn (1973) concluded that most continuous permafrost is in balance with the present climate at its upper surface, but changes at the base depend on the present climate and geothermal heat flow; in contrast, most discontinuous permafrost is probably unstable or "in such delicate equilibrium that the slightest climatic or surface change will have drastic disequilibrium effects".[18] Under warming conditions, the increasing depth of the summer active layer has significant impacts on the hydrologic and geomorphic regimes. Thawing and retreat of permafrost have been reported in the upper Mackenzie Valley and along the southern margin of its occurrence in Manitoba, but such observations are not readily quantified and generalized. Based on average latitudinal gradients of air temperature, an average northward displacement of the southern permafrost boundary by 50-to-150 km could be expected, under equilibrium conditions, for a 1°C warming. Only a fraction of the permafrost zone consists of actual ground ice. The remainder (dry permafrost) is simply soil or rock at subfreezing temperatures. The ice volume is generally greatest in the uppermost permafrost layers and mainly comprises pore and segregated ice in Earth material. Measurements of bore-hole temperatures in permafrost can be used as indicators of net changes in temperature regime. Gold and Lachenbruch (1973) infer a 2-4°C warming over 75 to 100 years at Cape Thompson, Alaska, where the upper 25% of the 400-m thick permafrost is unstable with respect to an equilibrium profile of temperature with depth (for the present mean annual surface temperature of -5°C). Maritime influences may have biased this estimate, however. At Prudhoe Bay similar data imply a 1.8°C warming over the last 100 years (Lachenbruch et al. 1982). Further complications may be introduced by changes in snow-cover depths and the natural or artificial disturbance of the surface vegetation. The potential rates of permafrost thawing have been established by Osterkamp (1984) to be two centuries or less for 25-meter-thick permafrost in the discontinuous zone of interior Alaska, assuming warming from -0.4 to 0°C in 3–4 years, followed by a further 2.6°C rise. Although the response of permafrost (depth) to temperature change is typically a very slow process (Osterkamp 1984; Koster 1993), there is ample evidence for the fact that the active layer thickness quickly responds to a temperature change (Kane et al. 1991). Whether, under a warming or cooling scenario, global climate change will have a significant effect on the duration of frost-free periods in both regions with seasonally- and perennially-frozen ground.

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Cryosphere

Glaciers and ice sheets Ice sheets and glaciers are flowing ice masses that rest on solid land. They are controlled by snow accumulation, surface and basal melt, calving into surrounding oceans or lakes and internal dynamics. The latter results from gravity-driven creep flow ("glacial flow") within the ice body and sliding on the underlying land, which leads to thinning and horizontal spreading.[19] Any imbalance of this dynamic equilibrium between mass gain, loss and transport due to flow results in either growing or shrinking ice bodies. Ice sheets are the greatest potential source of global freshwater, holding approximately 77% of the global total. This corresponds to 80 m of world sea-level equivalent, with Antarctica ing for 90% of this. Greenland s for most of the remaining 10%, with other ice bodies and glaciers ing for less than 0.5%. Because of their size in relation to annual rates of snow accumulation and melt, the residence time of water in ice sheets can extend to 100,000 or 1 million years. Consequently, any climatic perturbations produce slow responses, occurring over glacial and interglacial periods. Valley glaciers respond rapidly to climatic fluctuations with typical response times of 10–50 years.[20] However, the response of individual glaciers may be asynchronous to the same climatic forcing because of differences in glacier length, elevation, slope, and speed of motion. Oerlemans (1994) provided evidence of coherent global glacier retreat which could be explained by a linear warming trend of 0.66°C per 100 years.[20] While glacier variations are likely to have minimal effects upon global climate, their recession may have contributed one third to one half of the observed 20th Century rise in sea level (Meier 1984; IPCC 1996). Furthermore, it is extremely likely that such extensive glacier recession as is currently observed in the Western Cordillera of North America ,[21] where runoff from glacierized basins is used for irrigation and hydropower, involves significant hydrological and ecosystem impacts. Effective water-resource planning and impact mitigation in such areas depends upon developing a sophisticated knowledge of the status of glacier ice and the mechanisms that cause it to change. Furthermore, a clear understanding of the mechanisms at work is crucial to interpreting the global-change signals that are contained in the time series of glacier mass balance records. Combined glacier mass balance estimates of the large ice sheets carry an uncertainty of about 20%. Studies based on estimated snowfall and mass output tend to indicate that the ice sheets are near balance or taking some water out of the oceans.[22] Marinebased studies [23] suggest sea-level rise from the Antarctic or rapid ice-shelf basal melting. Some authors (Paterson 1993; Alley 1997) have suggested that the difference between the observed rate of sea-level rise (roughly 2 mm/y) and the explained rate of sea-level rise from melting of mountain glaciers, thermal expansion of the ocean, etc. (roughly 1 mm/y or less) is similar to the modeled imbalance in the Antarctic (roughly 1 mm/y of sea-level rise; Huybrechts 1990), suggesting a contribution of sea-level rise from the Antarctic. Relationships between global climate and changes in ice extent are complex. The mass balance of land-based glaciers and ice sheets is determined by the accumulation of snow, mostly in winter, and warm-season ablation due primarily to net radiation and turbulent heat fluxes to melting ice and snow from warm-air advection ,[24] [25] (Munro 1990). However, most of Antarctica never experiences surface melting.[26] Where ice masses terminate in the ocean, iceberg calving is the major contributor to mass loss. In this situation, the ice margin may extend out into deep water as a floating ice shelf, such as that in the Ross Sea. Despite the possibility that global warming could result in losses to the Greenland ice sheet being offset by gains to the Antarctic ice sheet,[27] there is major concern about the possibility of a West Antarctic Ice Sheet collapse. The West Antarctic Ice Sheet is grounded on bedrock below sea level, and its collapse has the potential of raising the world sea level 6–7 m over a few hundred years. Most of the discharge of the West Antarctic Ice Sheet is via the five major ice streams (faster flowing ice) entering the Ross Ice Shelf, the Rutford Ice Stream entering Ronne-Filchner shelf of the Weddell Sea, and the Thwaites Glacier and Pine Island Glacier entering the Amundsen Ice Shelf. Opinions differ as to the present mass balance of these systems (Bentley 1983, 1985), principally because of the limited data. The West Antarctic Ice Sheet is stable so long as the Ross Ice Shelf is constrained by drag along its lateral boundaries and pinned by local grounding.

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References [1] http:/ / maps. grida. no/ go/ graphic/ cryosphere [2] Hall, D. K., 1996: Remote sensing applications to hydrology: imaging radar. Hydrological Sciences, 41, 609-624. [3] Groisman, P. Ya, T. R. Karl, and R. W. Knight, 1994a: Observed impact of snow cover on the heat balance and the rise of continental spring temperatures. Science, 363, 198-200. [4] Lynch-Stieglitz, M., 1994: The development and validation of a simple snow model for the GISS GCM. J. Climate, 7, 1842-1855. [5] Cohen, J., and D. Rind, 1991: The effect of snow cover on the climate. J. Climate, 4, 689-706. [6] Vernekar, A. D., J. Zhou, and J. Shukla, 1995: The effect of Eurasian snow cover on the Indian monsoon. J. Climate, 8, 248-266. [7] Gutzler, D. S., and J. W. Preston, 1997: Evidence for a relationship between spring snow cover in North America and summer rainfall in New Mexico. Geophys. Res. Lett., 24, 2207-2210. [8] Robinson, D. A., K. F. Dewey, and R. R. Heim, 1993: Global snow cover monitoring: an update. Bull. Amer. Meteorol. Soc., 74, 1689-1696. [9] Groisman, P. Ya, and D. R. Easterling, 1994: Variability and trends of total precipitation and snowfall over the United States and Canada. J. Climate, 7, 184-205. [10] Brown, R. D., 1997: Historical variability in Northern Hemisphere spring snow covered area. Annals of Glaciology, 25 (in press). Axel Heiberg Island, N.W.T., Canada, 1960-91. J. Glaciology, 42(142): 548-563. [11] Prinsenberg, S. J. 1988: Ice-cover and ice-ridge contributions to the freshwater contents of Hudson Bay and Foxe Basin. Arctic, 41, 6-11. [12] Zwally, H. J., J. C. Comiso, C. L. Parkinson, W. J. Campbell, F. D. Carsey, and P. Gloersen, 1983: Antarctic Sea Ice, 1973-1976: Satellite ive-Microwave Observations. NASA SP-459, National Aeronautics and Space istration, Washington, D.C., 206 pp. [13] Gloersen, P., W. J. Campbell, D. J. Cavalieri, J. C. Comiso, C. L. Parkinson, and H. J. Zwally, 1992: Arctic and Antarctic Sea Ice, 1978-1987: Satellite ive-Microwave Observations and Analysis. NASA SP-511, National Aeronautics and Space istration, Washington, D.C., 290 pp. [14] Parkinson, C. L., J. C. Comiso, H. J. Zwally, D. J. Cavalieri, P. Gloersen, and W. J. Campbell, 1987: Arctic Sea Ice, 1973-1976: Satellite ive-Microwave Observations, NASA SP-489, National Aeronautics and Space istration, Washington, D.C., 296 pp. [15] Parkinson, C. L., 1995: Recent sea-ice advances in Baffin Bay/Davis Strait and retreats in the Bellinshausen Sea. Annals of Glaciology, 21, 348-352. [16] Johannessen, O. M., M. Miles, and E. Bjørgo, 1995: The Arctic’s shrinking sea ice. Nature, 376, 126-127. [17] Cavalieri, D. J., P. Gloersen, C. L. Parkinson, J. C. Comiso, and H. J. Zwally, 1997: Observed hemispheric asymmetry in global sea ice changes. Science, 278, 1104-1106. [18] Washburn, A. L., 1973: Periglacial processes and environments. Edward Arnold, London, 320 pp. p.48 [19] Greve, R.; Blatter, H. (2009). Dynamics of Ice Sheets and Glaciers. Springer. doi:10.1007/978-3-642-03415-2. ISBN 978-3-642-03414-5. [20] Oerlemans, J., 1994: Quantifying global warming from the retreat of glaciers. Science, 264, 243-245. [21] Pelto, M. S., 1996: Annual net balance of North Cascade Glaciers, 1984-94. J. Glaciology, 42, 3-9. [22] Bentley, C. R., and M. B. Giovinetto, 1991: Mass balance of Antarctica and sea level change. In: G. Weller, C. L. Wilson and B. A. B. Severin (eds.), Polar regions and climate change. University of Alaska, Fairbanks, p. 481-488. [23] Jacobs, S. S., H. H. Helmer, C. S. M. Doake, A. Jenkins, and R. M. Frohlich, 1992: Melting of ice shelves and the mass balance of Antarctica. J. Glaciology, 38, 375-387. [24] Paterson, W. S. B., 1993: World sea level and the present mass balance of the Antarctic ice sheet. In: W.R. Peltier (ed.), Ice in the Climate System, NATO ASI Series, I12, Springer-Verlag, Berlin, 131-140. [25] Van den Broeke, M. R., 1996: The atmospheric boundary layer over ice sheets and glaciers. Utrecht, Universitiet Utrecht, 178 pp.. [26] Van den Broeke, M. R., and R. Bintanja, 1995: The interaction of katabatic wind and the formation of blue ice areas in East Antarctica. J. Glaciology, 41, 395-407 [27] Ohmura, A., M. Wild, and L. Bengtsson, 1996: A possible change in mass balance of the Greenland and Antarctic ice sheets in the coming century. J. Climate, 9, 2124-2135.

Further reading Brown, R. D., and P. Cote, 1992: Interannual variability in landfast ice thickness in the Canadian High Arctic, 1950-89. Arctic, 45, 273-284. Brown, R. D., and B. E. Goodison, 1996: Interannual variability in reconstructed Canadian snow cover, 1915-1992. J. Climate, 9, 1299-1318. Chahine, M. T., 1992: The hydrological cycle and its influence on climate. Nature, 359, 373-380. Flato, G. M., and R. D. Brown, 1996: Variability and climate sensitivity of landfast Arctic sea ice. J. Geophys. Res., 101(C10), 25,767-25,777. Groisman, P. Ya, T. R. Karl, and R. W. Knight, 1994b: Changes of snow cover, temperature and radiative heat balance over the Northern Hemisphere. J. Climate, 7, 1633-1656.

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Cryosphere Harder, M., 1997: Role of precipitation in numerical simulations of arctic sea ice and related freshwater balance. Proc. Workshop on the implementation of the Arctic Precipitation Data Archive at the Global Precipitation Climatology Centre, WCRP-98, WMO/TD No. 804, 26-30. Hughes, M. G., A. Frei, and D. A. Robinson, 1996: Historical analysis of North American snow cover extent: merging satellite and station- derived snow cover observations. Proc. 53rd Eastern Snow Conference, Williamsburg, Virginia, 21-31. Huybrechts, P., 1990: The Antarctic ice sheet during the last glacialinterglacial cycle: a three-dimensional experiment. Annals of Glaciology, 14, 115-119. IPCC, 1996: Climate Change 1995: The Science of Climate Change. Houghton, J. T., L. G. Meira Filho, B. A. Callander, N. Harris, A. Kattenberg, and K. Maskell (eds.), Contribution of WGI to the Second Assessment Report of the Intergovernmental on Climate Change. Cambridge University Press, Cambridge, UK, 572 pp. Ledley, T. S., 1991: Snow on sea ice: competing effects in shaping climate. J. Geophys. Res., 96, 17,195-17,208. Ledley, T. S., 1993: Variations in snow on sea ice: a mechanism for producing climate variations. J. Geophys. Res., 98(D6), 10,401-10,410. Lynch-Stieglitz, M., 1994: The development and validation of a simple snow model for the GISS GCM. J. Climate, 7, 1842-1855. Martin, S., K. Steffen, J. Comiso, D. Cavalieri, M. R. Drinkwater, and B. Holt, 1992: Microwave remote sensing of polynyas. In: Carsey, F. D. (ed.), Microwave remote sensing of sea ice, Washington, DC, American Geophysical Union, 1992, 303-311. Meier, M. F., 1984: Contribution of small glaciers to global sea level rise. Science, 226, 1418-1421. Parkinson, C. L., J. C. Comiso, H. J. Zwally, D. J. Cavalieri, P. Gloersen, and W. J. Campbell, 1987: Arctic Sea Ice, 1973-1976: Satellite ive-Microwave Observations, NASA SP-489, National Aeronautics and Space istration, Washington, D.C., 296 pp. Paterson, W. S. B., 1993: World sea level and the present mass balance of the Antarctic ice sheet. In: W.R. Peltier (ed.), Ice in the Climate System, NATO ASI Series, I12, Springer-Verlag, Berlin, 131-140. Robinson, D. A., K. F. Dewey, and R. R. Heim, 1993: Global snow cover monitoring: an update. Bull. Amer. Meteorol. Soc., 74, 1689-1696. Steffen, K., and A. Ohmura, 1985: Heat exchange and surface conditions in North Water, northern Baffin Bay. Annals of Glaciology, 6, 178-181. Van den Broeke, M. R., 1996: The atmospheric boundary layer over ice sheets and glaciers. Utrecht, Universitiet Utrecht, 178 pp. Van den Broeke, M. R., and R. Bintanja, 1995: The interaction of katabatic wind and the formation of blue ice areas in East Antarctica. J. Glaciology, 41, 395-407. Welch, H. E., 1992: Energy flow through the marine ecosystem of the Lancaster Sound region, Arctic Canada. Arctic, 45, 343. B. E. Goodison, R. D. Brown, and R. G. Crane. (1999). Chapter 6: Cyrospheric systems (http:/ / eospso. gsfc. nasa. gov/science_plan/Ch6.pdf). Earth Observing System (EOS) Science Plan. NASA. Olav Slaymaker and Richard E J Kelly. The cryosphere and global environmental change. Malden, Mass.: Blackwell. ISBN 140512976X.

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External links • International Association of Cryospheric Sciences (IACS) (http://www.cryosphericsciences.org/) • International Glaciological Society (IGS) (http://www.igsoc.org/) • Global Outlook for Ice and Snow (http://www.unep.org/geo/geo_ice/) Assessment on the state and future of the Cryosphere, by the UN Environment Programme, June 2007 • Cryosphere overview map, from the UN Environment Programme (http://maps.grida.no/go/graphic/ cryosphere) • Department of Atmospheric Sciences at the University of Illinois: Cryosphere Today (http://arctic.atmos.uiuc. edu/cryosphere/) • Canadian Cryospheric Information Network (http://www.ccin.ca/) • State of the Canadian Cryosphere (http://www.socc.ca/) • Near-real-time overview of global ice concentration and snow extent (http://nsidc.org/cryosphere/glance/) • National Snow and Ice Data Center (http://nsidc.org) • ResearchChannel – Cryospheric Response to Climate Change (http://www.researchchannel.org/prog/ displayevent.aspx?rID=23653&fID=345). A video produced by the University of Washington, March 2008

Magnetosphere A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter, Saturn, Uranus, and Neptune. Jupiter's moon Ganymede has a small magnetosphere — but it is situated entirely within the magnetosphere of Jupiter, leading to complex interactions. The ionospheres of weakly magnetized planets such as Venus and Mars set up currents that partially deflect the solar wind flow, but do not have magnetospheres, per se. The term magnetosphere has also been used to describe regions dominated by the magnetic fields of celestial objects, e.g. pulsar magnetospheres.

History of magnetospheric physics The Earth's magnetosphere was discovered in 1958 by Explorer 1 during the research performed for the International Geophysical Year. Before this, scientists knew that electric currents existed in space, because solar eruptions sometimes led to "magnetic storm" disturbances. No one knew, however, where those currents were Artistic rendition of a magnetosphere. and why, or that the solar wind existed. In August and September 1958, Project Argus was performed to test a theory about the formation of radiation belts that may have tactical use in war. In 1959 Thomas Gold proposed the name "magnetosphere" when he wrote: "The region above the ionosphere in which the magnetic field of the earth has a dominant control over the motions of gas and fast charged particles is known to extend out to a distance of the order of 10 earth radii; it

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may appropriately be called the magnetosphere" [Gold, Journal of Geophysical Research, volume 64, page 1219, 1959].

Earth's magnetosphere The magnetosphere of Earth is a region in space whose shape is determined by the Earth's internal magnetic field, the solar wind plasma, and the interplanetary magnetic field (IMF). In the magnetosphere, a mix of free ions and electrons from both the solar wind and the Earth's ionosphere is confined by electromagnetic forces that are much stronger than gravity and collisions. Despite its name, the magnetosphere is distinctly non-spherical. All known planetary magnetospheres in the solar system possess more of an oval tear-drop shape because of the solar wind.

Schematic of Earth's magnetosphere. The solar wind flows from left to right.

On the side facing the Sun, the distance to its boundary (which varies with solar wind intensity) is about 70,000 km (10-12 Earth radii or RE, where 1 RE = 6371 km; unless otherwise noted, all distances here are from the Earth's center). The boundary of the magnetosphere ("magnetopause") is roughly bullet shaped, about 15 RE abreast of Earth and on the night side (in the "magnetotail" or "geotail") approaching a cylinder with a radius 20-25 RE. The tail region stretches well past 200 RE, and the way it ends is not well-known. The outer neutral gas envelope of Earth, or geocorona, consists mostly of the lightest atoms, hydrogen and helium, and continues beyond 4-5 RE, with diminishing density. The hot plasma ions of the magnetosphere acquire electrons during collisions with these atoms and create an escaping "glow" of energetic neutral atoms (ENAs) that have been used to image the hot plasma clouds by the IMAGE and TWINS missions. The upward extension of the ionosphere, known as the plasmasphere, also extends beyond 4-5 RE with diminishing density, beyond which it becomes a flow of light ions called the polar wind that escapes out of the magnetosphere into the solar wind. Energy deposited in the ionosphere by auroras strongly heats the heavier atmospheric components such as oxygen and molecules of oxygen and nitrogen, which would not otherwise escape from Earth's gravity. Owing to this highly variable heating, however, a heavy atmospheric or ionospheric outflow of plasma flows during disturbed periods from the auroral zones into the magnetosphere, extending the region dominated by terrestrial material, known as the fourth or plasma geosphere, at times out to the magnetopause. Earth’s magnetosphere provides protection, without which life as we know it could not survive. Mars, with little or no magnetic field is thought to have lost much of its former oceans and atmosphere to space in part due to the direct impact of the solar wind. Venus with its thick atmosphere is thought to have lost most of its water to space in large part owing to solar wind ablation.[1] Due to the size of the Jupiter's magnetosphere there is a possibility of very weak and very brief seasonal head-tail interaction between Earth's magnetosphere and Jupiter's magnetosphere. The magnetospheres of the outer gas planets may weakly interact, although their magnetospheres are much smaller than Jupiter's.

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General properties Two factors determine the structure and behavior of the magnetosphere: (1) The internal field of the Earth, and (2) The solar wind. 1. The internal field of the Earth (its "main field") appears to be generated in the Earth's core by a dynamo process, associated with the circulation of liquid metal in the core, driven by internal heat sources. Its major part resembles the field of a bar magnet ("dipole field") inclined by about 10° to the rotation axis of Earth, but more complex parts ("higher harmonics") also exist, as first shown by Carl Friedrich Gauss. The dipole field has an intensity of about 30,000-60,000 nanoteslas (nT) at the Earth's surface, and its intensity diminishes like the inverse of the cube of the distance, i.e. at a distance of R Earth radii it only amounts to 1/8 of the surface field in the same direction. Higher harmonics diminish faster, like higher powers of 1/R, making the dipole field the only important internal source in most of the magnetosphere.

Density and temperature of plasma in the magnetosphere and other areas of space. Density increases upwards, temperature increases towards the right. The free electrons in a metal may be considered an [2] electron plasma

2. The solar wind is a fast outflow of hot plasma from the sun in all directions. Above the sun's equator it typically attains 400 km/s; above the sun's poles, up to twice as much. The flow is powered by the million-degree temperature of the sun's corona, for which no generally accepted explanation exists yet. Its composition resembles that of the Sun—about 95% of the ions are protons, about 4% helium nuclei, with 1% of heavier matter (C, N, O, Ne, Si, Mg...up to Fe) and enough electrons to keep charge neutrality. At Earth's orbit its typical density is 6 ions/cm3 (variable, as is the velocity), and it contains a variable interplanetary magnetic field (IMF) of (typically) 2–5 nT. The IMF is produced by stretched-out magnetic field lines originating on the Sun, a process described in the article Geomagnetic storm. Physical reasons make it difficult for solar wind plasma WITH its embedded IMF to mix with terrestrial plasma whose magnetic field has a different source. The two plasmas end up separated by a boundary, the magnetopause, and the Earth's plasma is confined to a cavity inside the flowing solar wind, the magnetosphere. The isolation is not complete, thanks to secondary processes such as magnetic reconnection —otherwise it would be hard for the solar wind to transmit much energy to the magnetosphere—but it still determines the overall configuration. An additional feature is a collision-free bow shock which forms in the solar wind ahead of Earth, typically at 13.5 RE on the sunward side. It forms because the solar velocity of the wind exceeds (typically 2–3 times) that of Alfvén waves, a family of characteristic waves with which disturbances propagate in a magnetized fluid. In the region behind the shock ("magnetosheath") the velocity drops briefly to the Alfvén velocity (and the temperature rises, absorbing lost kinetic energy), but the velocity soon rises back as plasma is dragged forward by the surrounding solar wind flow. To understand the magnetosphere, one needs to visualize its magnetic field lines, that everywhere point in the direction of the magnetic field—e.g., diverging out near the magnetic north pole (or geographic southpole), and converging again around the magnetic south pole (or the geographic northpole), where they enter the Earth. They can be visualized like wires which tie the magnetosphere together—wires that also guide the motions of trapped particles, which slide along them like beads (though other motions may also occur).

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Radiation belts When the first scientific satellites were launched in the first half of 1958—Explorers 1 and 3 by the US, Sputnik 3 by the Soviet Union—they observed an intense (and unexpected) radiation belt around Earth, held by its magnetic field. "My God, Space is Radioactive!" exclaimed one of Van Allen's colleagues, when the meaning of those observations was realized. That was the "inner radiation belt" of protons with energies in the range 10-100 MeV (megaelectronvolts), attributed later to "albedo neutron decay," a secondary effect of the interaction of cosmic radiation with the upper atmosphere. It is centered on field lines crossing the equator about 1.5 RE from the Earth's center. Later a population of trapped ions and electrons was observed on field lines crossing the equator at 2.5–8 RE. The high-energy part of that population (about 1 MeV) became known as the "outer radiation belt", but its bulk is at lower energies (peak about 65 keV) and is identified as the ring current plasma. The trapping of charged particles in a magnetic field can be quite stable. This is particularly true in the inner belt, because the build-up of trapped protons from albedo neutrons is quite slow, requiring years to reach observed intensities. In July 1962, the United States tested a thermonuclear weapon high over the South Pacific at around 400 km in the upper atmosphere, in this region, creating an artificial belt of high-energy electrons, and some of them were still around 4–5 years later (such tests are now banned by treaty). The outer belt and ring current are less persistent, because charge-exchange collisions with atoms of the geocorona (see above) tends to remove their particles. That suggests the existence of an effective source mechanism, continually supplying this region with fresh plasma. It turns out that the magnetic barrier can be broken down by electric forces, as discussed in Magnetic Storms and Plasma Flows (MSPF). If plasma is pushed hard enough, it generates electric fields which allow it to move in response to the push, often (not always) deforming the magnetic field in the process.

Magnetic tails A magnetic tail or magnetotail is formed by pressure from the solar wind on a planet's magnetosphere. The magnetotail can extend great distances away from its originating planet. Earth's magnetic tail extends at least 200 Earth radii in the anti-sunward direction well beyond the orbit of the Moon at about 60 Earth radii, while Jupiter's magnetic tail extends beyond the orbit of Saturn. On occasion Saturn is immersed inside the Jovian magnetosphere. The extended magnetotail results from energy stored in the planet's magnetic field. At times this energy is released and the magnetic field becomes temporarily more dipole-like. As it does so that stored energy goes to energize plasma trapped on the involved magnetic field lines. Some of that plasma is driven tailward and into the distant solar wind. The rest is injected into the inner magnetosphere where it results in the aurora and the ring current plasma population. The resulting energetic plasma and electric currents can disrupt spacecraft operations, communication and navigation.

A view from the IMAGE satellite showing Earth's plasmasphere using its Extreme Ultraviolet (EUV) imager instrument.

Magnetosphere

Electric currents in space Magnetic fields in the magnetosphere arise from the Earth's internal magnetic field as well as from electric currents that flow in the magnetospheric plasma: the plasma acts as an electromagnet. Magnetic fields from currents that circulate in the magnetospheric plasma extend the Earth's magnetism much further in space than would be predicted from the Earth's internal field alone. Such currents also determine the field's structure far from Earth, creating the regions described in the introduction above. Unlike in a conventional resistive electric circuit, where currents are best thought of as arising as a response to an applied voltage, currents in the magnetosphere are better seen as caused by the structure and motion of the plasma in its associated magnetic field. For instance, electrons and positive ions trapped in the dipole-like field near the Earth tend to circulate around the magnetic axis of the dipole (the line connecting the magnetic poles) in a ring around the Earth, without gaining or losing energy (this is known as Guiding center motion). Viewed from above the magnetic north pole (geographic south), ions circulate clockwise, electrons counterclockwise, producing a net circulating clockwise current, known (from its shape) as the ring current. No voltage is needed—the current arises naturally from the motion of the ions and electrons in the magnetic field. Any such current will modify the magnetic field. The ring current, for instance, strengthens the field on its outside, helping expand the size of the magnetosphere. At the same time, it weakens the magnetic field in its interior. In a magnetic storm, plasma is added to the ring current, making it temporarily stronger, and the field at Earth is observed to weaken by up to 1-2%. The deformation of the magnetic field, and the flow of electric currents in it, are intimately linked, making it often hard to label one as cause and the other as effect. Frequently (as in the magnetopause and the magnetotail) it is intuitively more useful to regard the distribution and flow of plasma as the primary effect, producing the observed magnetic structure, with the associated electric currents just one feature of those structures, more of a consistency requirement of the magnetic structure. As noted, one exception (at least) exists, a case where voltages do drive currents. That happens with Birkeland currents, which flow from distant space into the near-polar ionosphere, continue at least some distance in the ionosphere, and then return to space. (Part of the current then detours and leaves Earth again along field lines on the morning side, flows across midnight as part of the ring current, then comes back to the ionosphere along field lines on the evening side and res the pattern.) The full circuit of those currents, under various conditions, is still under debate. Because the ionosphere is an ohmic conductor of sorts, such flow will heat it up. It will also create secondary Hall currents, and accelerate magnetospheric particles—electrons in the arcs of the polar aurora, and singly-ionized oxygen ions (O+) which contribute to the ring current.

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Classification of magnetic fields Regardless of whether they are viewed as sources or consequences of the magnetospheric field structure, electric currents flow in closed circuits. That makes them useful for classifying different parts of the magnetic field of the magnetosphere, each associated with a distinct type of circuit. In this way the field of the magnetosphere is often resolved into 5 distinct parts, as follows. 1. The internal field of the Earth ("main field") arising from electric currents in the core. It is dipole-like, modified by higher harmonic contributions. Schematic view of the different current systems 2. The ring current field, carried by plasma trapped in the dipole-like which shape the Earth's magnetosphere field around Earth, typically at distances 3–8 RE (less during large storms). Its current flows (approximately) around the magnetic equator, mainly clockwise when viewed from north. (A small counterclockwise ring current flows at the inner edge of the ring, caused by the fall-off in plasma density as Earth is approached.) 3. The field confining the Earth's plasma and magnetic field inside the magnetospheric cavity. The currents responsible for it flow on the magnetopause, the interface between the magnetosphere and the solar wind, described in the introduction. Their flow, again, may be viewed as arising from the geometry of the magnetic field (rather than from any driving voltage), a consequence of "Ampére's law" (embodied in Maxwell's equations) which in this case requires an electric current to flow along any interface between magnetic fields of different directions and/or intensities. 4. The system of tail currents. The magnetotail consists of twin bundles of oppositely directed magnetic field (the "tail lobes"), directed earthwards in the northern half of the tail and away from Earth in the southern half. In between the two exists a layer ("plasma sheet") of denser plasma (0.3-0.5 ions/cm3 versus 0.01-0.02 in the lobes), and because of the difference between the ading magnetic fields, by Ampére's law an electric current flows there too, directed from dawn to dusk. The flow closes (as it must) by following the tail magnetopause—part over the northern lobe, part over the southern one. 5. The Birkeland current field (and its branches in the ionosphere and ring current), a circuit is associated with the polar aurora. Unlike the 3 preceding current systems, it does require a constant input of energy, to provide the heating of its ionospheric path and the acceleration of auroral electrons and of positive ions. The energy probably comes from a dynamo process, meaning that part of the circuit threads a plasma moving relative to Earth, either in the solar wind and in "boundary layer" flows which it drives just inside the magnetopause, or by plasma moving earthward in the magnetotail, as observed during substorms (below).

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Magnetic substorms and storms Earlier it was stated that, "if plasma is pushed hard enough, it generates electric fields which allow it to move in response to the push, often (not always) deforming the magnetic field in the process." Two examples of such "pushing" are particularly important in the magnetosphere. The THEMIS mission is a NASA program to study in detail the physical processes involved in substorms. The more common one occurs when the north-south component Bz of the interplanetary magnetic field (IMF) is appreciable and points southward. In this state field lines of the magnetosphere are relatively strongly linked to the IMF, allowing energy and plasma to enter it at relatively high rates. This swells up the magnetotail and makes it unstable. Ultimately the tail's structure changes abruptly and violently, a process known as a magnetic substorm. One possible scenario (the subject is still debated) is as follows. As the magnetotail swells, it creates a wider obstacle to the solar wind flow, causing its widening portion to be squeezed more by the solar wind. In the end, this squeezing breaks apart field lines in the plasma sheet ("magnetic reconnection"), and the distant part of the sheet, no longer attached to the Earth, is swept away as an independent magnetic structure ("plasmoid"). The near-Earth part Magnetic reconnection in the near-Earth magnetotail, producing a disconnected snaps back earthwards, energizing its "plasmoid" particles and producing Birkeland currents and bright auroras. As observed in the 1970s by the ATS satellites at 6.6 RE, when conditions are favorable that can happen up to several times a day. Substorms generally do not substantially add to the ring current. That happens in magnetic storms, when following an eruption on the sun (a "coronal mass ejection" or a "solar flare"—details are still debated, see MSPF) a fast-moving plasma cloud hits the Earth. If the IMF has a southward component, this not only pushes the magnetopause boundary closer to Earth (at times to about half its usual distance), but it also produces an injection of plasma from the tail, much more vigorous than the one associated with substorms. The plasma population of the ring current may now grow substantially, and a notable part of the addition consists of O+ oxygen ions extracted from the ionosphere as a by-product of the polar aurora. In addition, the ring current is driven earthward (which energizes its particles further), temporarily modifying the field around the Earth and thus shifting the aurora (and its current system) closer to the equator. The magnetic disturbance may decay within 1–3 days as many ions are removed by charge exchange, but the higher energies of the ring current can persist much longer.

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References [1] "Polar Substorm" (http:/ / science. nasa. gov/ science-news/ science-at-nasa/ 2000/ ast02mar_1m/ ). NASA Science News. 2009-03-02. . Retrieved 2010-12-28. [2] After Peratt, A. L., " Advances in Numerical Modeling of Astrophysical and Space Plasmas (http:/ / adsabs. harvard. edu/ cgi-bin/ nph-bib_query?1996Ap& SS. 242. . . 93P)" (1966) Astrophysics and Space Science, v. 242, Issue 1/2, p. 93-163.

• Introduction to Geomagnetically Trapped Radiation by Martin Walt (1994) • Storms from the Sun by M. Carlowicz and R. Lopez"(2002)" • D. P. Stern, M. Peredo (2004-09-28). "The Exploration of the Earth's Magnetosphere" (http://www-istp.gsfc. nasa.gov/Education/Intro.html). NASA. Retrieved 2006-08-22.

External links • • • •

USGS Geomagnetism Program (http://geomag.usgs.gov) Aurora borealis (http://www.auroresboreales.com) Storms from the Sun - The Emerging Science of Space Weather (http://www.stormsfromthesun.net) Magnetosphere: Earth's Magnetic Shield Against the Solar Wind (http://meted.ucar.edu/hao/aurora/txt/ x_m_0.php) • Physics of the Aurora (http://meted.ucar.edu/hao/aurora/) • " 3D Earth Magnetic Field Charged-Particle Simulator (http://www.bartol.udel.edu/~kowocki/)" Tool dedicated to the 3d simulation of charged particles in the magnetosphere.. [VRML Plug-in Required] • " Exploration of the Earth's Magnetosphere (http://www.phy6.org/Education/Intro.html)", Educational web site by David P. Stern and Mauricio Peredo

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Branches of earth science Geology Geology (from the Greek γῆ, gê, "earth" and λόγος, logos, "study") is the science and study of the solid Earth and the processes by which it is shaped and changed. Geology provides primary evidence for plate tectonics, the history of life and evolution, and past climates. In modern times, geology is commercially important for mineral and hydrocarbon exploration, evaluating water resources, is publicly important for predicting and understanding natural hazards, understanding and remediating environmental problems, and understanding past climate change, plays an essential role in geotechnical engineering, and is a major academic discipline.

History

Students examining the Wasatch Fault near Salt Lake City, Utah.

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The study of the physical material of the Earth dates back at least to ancient Greece when Theophrastus (372-287 BC) wrote the work Peri Lithon (On Stones). In the Roman period, Pliny the Elder wrote in detail of the many minerals and metals then in practical use, and correctly noted the origin of amber. Some modern scholars, such as Fielding H. Garrison, are of the opinion that modern geology began in the medieval Islamic world.[2] Abu al-Rayhan al-Biruni (973–1048 AD) was one of the earliest Muslim geologists, whose works included the earliest writings on the geology of India, hypothesizing that the Indian subcontinent was once a sea.[3] Islamic Scholar Ibn Sina (Avicenna, 981–1037) proposed detailed explanations for the formation of mountains, the origin of earthquakes, and other topics central to modern Geology, which provided an essential foundation for the later development of the science.[4] In China, the polymath Shen Kua (1031–1095) formulated a hypothesis for the process of land formation: based on his observation of fossil animal shells in a geological stratum in a mountain hundreds of miles from the ocean, he inferred that the land was formed by erosion of the mountains and by deposition of silt.

William Smith's geologic map of England, Wales, and southern Scotland. Completed in 1815, it was the first national-scale geologic map, and by far [1] the most accurate of its time.

Nicolas Steno (1638–1686) is credited with the law of superposition, the principle of original horizontality, and the principle of lateral continuity: three defining principles of stratigraphy. The word geology was first used by Jean-André Deluc in 1778 and introduced as a fixed term by Horace-Bénédict de Saussure in 1779. The word is derived from the Greek γῆ, gê, meaning "earth" and λόγος, logos, meaning "speech".[5] William Smith (1769–1839) drew some of the first geological maps and began the process of ordering rock strata (layers) by examining the fossils contained in them.[1] James Hutton is often viewed as the first modern geologist.[6] In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh. In his paper, he explained his theory that the Earth must be much older than had previously been supposed in order to allow enough time for mountains to be eroded and for sediments to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. Hutton published a two-volume version of his ideas in 1795 (Vol. 1 [7], Vol. 2 [8]). Followers of Hutton were known as Plutonists because they believed that some rocks were formed by vulcanism which is the deposition of lava from volcanoes, as opposed to the Neptunists, who believed that all rocks had settled out of a large ocean whose level gradually dropped over time. Sir Charles Lyell first published his famous book, Principles of Geology,[9] in 1830. The book, which influenced the thought of Charles Darwin, successfully promoted the doctrine of uniformitarianism. This theory states that slow geological processes have occurred throughout the Earth's history and are still occurring today. In contrast, catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time. Much of 19th-century geology revolved around the question of the Earth's exact age. Estimates varied from a few 100,000 to billions of years.[10] By the early 20th century, radiometric dating allowed the Earth's age to be estimated at two billion years. The awareness of this vast amount of time opened the door to new theories about the processes that shaped the planet.

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The most significant advances in 20th century geology have been the development of the theory of plate tectonics in the 1960s, and the refinement of estimates of the planet's age. Plate tectonic theory arose out of two separate geological observations: seafloor spreading and continental drift. The theory revolutionized the Earth sciences. Today the Earth is known to be approximately 4.5 billion years old.[11]

Geologic time The geologic time scale encomes the history of the Earth.[12] It is bracketed at the old end by the dates of the earliest solar system material at 4.567 Ga,[13] (gigaannum: billion years ago) and the age of the Earth at 4.54 Ga[14] [15] at the beginning of the informally recognized Hadean eon. At the young end of the scale, it is bracketed by the present day in the Holocene epoch.

Important milestones • 4.567 Ga: Solar system formation[13] • 4.54 Ga: Accretion of Earth[14] [15] • c. 4 Ga: End of Late Heavy Bombardment, first life • c. 3.5 Ga: Start of photosynthesis • c. 2.3 Ga: Oxygenated atmosphere, first snowball Earth

Geological time put in a diagram called a geological clock, showing the relative lengths of the eons of the Earth's history.

• 730–635 Ma (megaannum: million years ago): two snowball Earths • 542± 0.3 Ma: Cambrian explosion – vast multiplication of hard-bodied life; first abundant fossils; start of the Paleozoic • c. 380 Ma: First vertebrate land animals • 250 Ma: Permian-Triassic extinction – 90% of all land animals die. End of Paleozoic and beginning of Mesozoic • 65 Ma: Cretaceous-Tertiary extinction – Dinosaurs die; end of Mesozoic and beginning of Cenozoic • c. 7 Ma – Present: Hominins • c. 7 Ma: First hominins appear • 3.9 Ma: First Australopithecus, direct ancestor to modern Homo sapiens, appear • 200 ka (kiloannum: thousand years ago): First modern Homo sapiens appear in East Africa

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Brief time scale The second and third timelines are each subsections of their preceding timeline as indicated by asterisks. The Holocene (the latest epoch) is too small to be shown clearly on this timeline.

Millions of Years

Relative and absolute dating Geological events can be given a precise date at a point in time, or they can be related to other events that came before and after them. Geologists use a variety of methods to give both relative and absolute dates to geological events. They then use these dates to find the rates at which processes occur. Relative dating Methods for relative dating were developed when geology first emerged as a formal science. Geologists still use the following principles today as a means to provide information about geologic history and the timing of geologic events. The principle of intrusive relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a Cross-cutting relations can be used to determine the relative ages of rock strata and other formation of sedimentary rock, it can geological structures. Explanations: A - folded rock strata cut by a thrust fault; B - large be determined that the igneous intrusion (cutting through A); C - erosional angular unconformity (cutting off A & B) on intrusion is younger than the which rock strata were deposited; D - volcanic dyke (cutting through A, B & C); E - even younger rock strata (overlying C & D); F - normal fault (cutting through A, B, C & E). sedimentary rock. There are a number of different types of intrusions, including stocks, laccoliths, batholiths, sills and dikes. The principle of cross-cutting relationships pertains to the formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether the fault is a normal fault or a thrust fault.[16] The principle of inclusions and components states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix. As a result, xenoliths are older than the rock which contains

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them. The principle of uniformitarianism states that the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time.[17] A fundamental principle of geology advanced by the 18th century Scottish physician and geologist James Hutton, is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now." The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments s this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal).[16] The principle of superposition states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. Logically a younger layer cannot slip beneath a layer previously deposited. This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed.[16]

The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is a great example of both Original Horozontality and the Law of Superposition. These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park. From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically ted, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone. Picture from Glen Canyon National Recreation Area, Utah.

The principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist at the same time period throughout the world, their presence or (sometimes) absence may be used to provide a relative age of the formations in which they are found. Based on principles laid out by William Smith almost a hundred years before the publication of Charles Darwin's theory of evolution, the principles of succession were developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilization, the localization of fossil types due to lateral changes in habitat (facies change in sedimentary strata), and that not all fossils may be found globally at the same time.[18] Absolute dating Geologists can also give precise absolute dates to geologic events. These dates are useful on their own, and can also be used in conjunction with relative dating methods or to calibrate relative dating methods.[19] A large advance in geology in the advent of the 20th century was the ability to give precise absolute dates to geologic events through radioactive isotopes and other methods. The advent of radiometric dating changed the understanding of geologic time. Before, geologists could only use fossils to date sections of rock relative to one another. With isotopic dates, absolute dating became possible, and these absolute dates could be applied fossil sequences in which there was datable material, converting the old relative ages into new absolute ages. For many geologic applications, isotope ratios are measured in minerals that give the amount of time that has ed since a rock ed through its particular closure temperature, the point at which different radiometric isotopes stop diffusing into and out of the crystal lattice.[20] [21] These are used in geochronologic and thermochronologic studies. Common methods include uranium-lead dating, potassium-argon dating and argon-argon dating, and

Geology uranium-thorium dating. These methods are used for a variety of applications. Dating of lavas and ash layers can help to date stratigraphy and calibrate relative dating techniques. These methods can also be used to determine ages of pluton emplacement. Thermochemical techniques can be used to determine temperature proiles within the crust, the uplift of mountain ranges, and paleotopography. Fractionation of the lanthanide series elements is used to compute ages since rocks were removed from the mantle. Other methods are used for more recent events. Optically stimulated luminescence and cosmogenic radionucleide dating are used to date surfaces and/or erosion rates. Dendrochronology can also be used for the dating of landscapes. Radiocarbon dating is used for young organic material.

Geologic materials The majority of geological data come from research on solid Earth materials. These typically fall into one of two categories: rock and unconsolidated material.

Rock There are three major types of rock: igneous, sedimentary, and metamorphic. The rock cycle is an important concept in geology which illustrates the relationships between these three types of rock, and magma. When a rock crystallizes from melt (magma and/or lava), it is an igneous rock. This rock can be weathered and eroded, and then redeposited and lithified into a sedimentary rock, or be turned into a metamorphic rock due to heat and pressure that change the mineral content of the rock and give it a characteristic fabric. The sedimentary rock can then be subsequently turned into a metamorphic rock due to heat and pressure, and the metamorphic rock can be weathered, eroded, deposited, and lithified, becoming a sedimentary rock. Sedimentary rock may also be re-eroded and This schematic diagram of the rock cycle shows the relationship between magma redeposited, and metamorphic rock may also and sedimentary, metamorphic, and igneous rock undergo additional metamorphism. All three types of rocks may be re-melted; when this happens, a new magma is formed, from which an igneous rock may once again crystallize. The majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth.

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Unconsolidated material Geologists also study unlithified material, which typically comes from more recent deposits. Because of this, the study of such material is often known as Quaternary geology, after the recent Quaternary Period. This includes the study of sediment and soils, and is important to some (or many) studies in geomorphology, sedimentology, and paleoclimatology.

Whole-Earth structure

Oceanic-continental convergence resulting in subduction and volcanic arcs illustrates one effect of plate tectonics.

Plate tectonics In the 1960s, a series of discoveries, the most important of which was seafloor spreading,[22] [23] showed that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into a number of tectonic plates that move across the plastically deforming, solid, upper mantle, which is called the asthenosphere. There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle: oceanic plate motions and mantle convection currents always move in the same direction, because the oceanic lithosphere is the rigid upper thermal boundary layer of the convecting mantle. This coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics.

On this diagram, subducting slabs are in blue, and continental margins and a few plate boundaries are in red. The blue blob in the cutaway section is the seismically imaged Farallon Plate, which is subducting beneath North America. The remnants of this plate on the Surface of the Earth are the Juan de Fuca Plate and Explorer plate in the Northwestern USA / Southwestern Canada, and the Cocos Plate on the west coast of Mexico.

The development of plate tectonics provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features could be explained as plate boundaries.[24] Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, were explained as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes were explained as convergent boundaries, where one plate subducts under another. Transform boundaries, such as the San Andreas fault system, resulted in widespread powerful earthquakes. Plate tectonics also provided a mechanism for Alfred Wegener's theory of continental drift,[25] in which the continents move across the surface of the Earth over geologic time. They also provided a driving force for crustal deformation, and a new setting for the observations of structural geology. The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convecting mantle.

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Earth structure Advances in seismology, computer modeling, and mineralogy and crystallography at high temperatures and pressures give insights into the internal composition and structure of the Earth.

The Earth's layered structure. (1) inner core; (2) outer core; (3) lower mantle; (4) upper mantle; (5) lithosphere; (6) crust

Seismologists can use the arrival times of seismic waves in reverse to image the interior of the Earth. Early advances in this field showed the existence of a liquid outer core (where shear waves were not able to propagate) and a dense solid inner core. These advances led to the development of a layered model of the Earth, with a crust and lithosphere on top, the mantle below (separated within itself by seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that. More recently, seismologists have been able to create detailed images of wave speeds inside the earth in the same way a doctor images a body in a CT scan. These images have led to a much more detailed view of the interior of the Earth, and have replaced the simplified layered model with a much more dynamic model. Mineralogists have been able to use the pressure and temperature data from the seismic and modelling studies alongside knowledge of the elemental composition of the Earth at depth to reproduce these conditions in experimental settings and measure changes in crystal structure. These studies explain the chemical changes associated with the major seismic discontinuities in the mantle, and show the crystallographic structures expected in the inner core of the Earth.

Earth layered structure. Typical wave paths from earthquakes like these gave early seismologists insights into the layered structure of the Earth

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Geological evolution of an area The geology of an area evolves through time as rock units are deposited and inserted and deformational processes change their shapes and locations. Rock units are first emplaced either by deposition onto the surface or intrusion into the overlying rock. Deposition can occur when sediments settle onto the surface of the Earth and later lithify into sedimentary rock, or when as volcanic material such as volcanic ash or lava flows blanket the surface. Igneous intrusions such as batholiths, laccoliths, dikes, and sills, push upwards into the overlying rock, and crystallize as they intrude.

An originally horizontal sequence of sedimentary rocks (in shades of tan) are affected by igneous activity. Deep below the surface are a magma chamber and large associated igneous bodies. The magma chamber feeds the volcano, and sends off shoots of magma that will later crystallize into dikes and sills. Magma also advances upwards to form intrusive igneous bodies. The diagram illustrates both a cinder cone volcano, which releases ash, and a composite volcano, which releases both lava and ash.

After the initial sequence of rocks has been deposited, the rock units can be deformed and/or metamorphosed. Deformation typically occurs as a result of horizontal shortening, horizontal extension, or side-to-side (strike-slip) motion. These structural regimes broadly relate to convergent boundaries, divergent boundaries, and transform boundaries, respectively, between tectonic plates. When rock units are placed under horizontal compression, they shorten and become thicker. Because rock units, other than muds, do not significantly change in volume, this is accomplished in two primary ways: through faulting and folding. In the shallow crust, where brittle deformation can occur, thrust faults form, which cause deeper rock to move on top of shallower rock. Because deeper rock is often older, as noted by the principle of superposition, this can result in older rocks moving on top of younger ones. Movement along faults can result in folding, either because the faults are not planar, or because the rock layers are dragged along, forming drag folds, as slip occurs are along the fault. Deeper in the

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74 Earth, rocks behave plastically, and fold instead of faulting. These folds can either be those where the material in the center of the fold buckles upwards, creating "antiforms", or where it buckles downwards, creating "synforms". If the tops of the rock units within the folds remain pointing upwards, they are called anticlines and synclines, respectively. If some of the units in the fold are facing downward, the structure is called an overturned anticline or syncline, and if all of the rock units are overturned or the correct up-direction is unknown, they are simply called by the most general , antiforms and synforms.

An illustration of the three types of faults. Strike-slip faults occur when rock units slide past one another, normal faults occur when rocks are undergoing horizontal extension, and thrust faults occur when rocks are undergoing horizontal shortening.

Even higher pressures and temperatures during horizontal shortening can cause both folding and metamorphism of the rocks. This metamorphism causes changes in the mineral composition of the rocks; creates a foliation, or planar surface, that is related to mineral growth under stress; and can remove signs of the original textures of the rocks, such as bedding in sedimentary rocks, flow features of lavas, and crystal patterns in crystalline rocks.

A diagram of folds, indicating an anticline and a syncline.

Extension causes the rock units as a whole to become longer and thinner. This is primarily accomplished through normal faulting and through the ductile stretching and thinning. Normal faults drop rock units that are higher below those that are lower. This typically results in younger units being placed below older units. Stretching of units can result in their thinning; in fact, there is a location within the Maria Fold and Thrust Belt in which the entire sedimentary sequence of the Grand Canyon can be seen over a length of less than a meter. Rocks at the depth to be ductilely stretched are often also metamorphosed. These stretched rocks can also pinch into lenses, known as boudins, after the French word for "sausage", because of their visual similarity.

Geology Where rock units slide past one another, strike-slip faults develop in shallow regions, and become shear zones at deeper depths where the rocks deform ductilely. The addition of new rock units, both depositionally and intrusively, often occurs during deformation. Faulting and other deformational processes result in the creation of topographic gradients, causing material on the rock unit that is increasing in elevation to be eroded by hillslopes and channels. These sediments are deposited on the rock unit that is going down. Continual motion along the fault maintains the topographic gradient in spite of the movement of sediment, and continues to create accommodation space for the material to deposit. Geologic cross-section of Kittatinny Mountain. Deformational events are often also associated with volcanism and This cross-section shows metamorphic rocks, igneous activity. Volcanic ashes and lavas accumulate on the surface, overlain by younger sediments deposited after the and igneous intrusions enter from below. Dikes, long, planar igneous metamorphic event. These rock units were later intrusions, enter along cracks, and therefore often form in large folded and faulted during the uplift of the mountain. numbers in areas that are being actively deformed. This can result in the emplacement of dike swarms, such as those that are observable across the Canadian shield, or rings of dikes around the lava tube of a volcano. All of these processes do not necessarily occur in a single environment, and do not necessarily occur in a single order. The Hawaiian Islands, for example, consist almost entirely of layered basaltic lava flows. The sedimentary sequences of the mid-continental United States and the Grand Canyon in the southwestern United States contain almost-undeformed stacks of sedimentary rocks that have remained in place since Cambrian time. Other areas are much more geologically complex. In the southwestern United States, sedimentary, volcanic, and intrusive rocks have been metamorphosed, faulted, foliated, and folded. Even older rocks, such as the Acasta gneiss of the Slave craton in northwestern Canada, the oldest known rock in the world have been metamorphosed to the point where their origin is undiscernable without laboratory analysis. In addition, these processes can occur in stages. In many places, the Grand Canyon in the southwestern United States being a very visible example, the lower rock units were metamorphosed and deformed, and then deformation ended and the upper, undeformed units were deposited. Although any amount of rock emplacement and rock deformation can occur, and they can occur any number of times, these concepts provide a guide to understanding the geological history of an area.

Methods of geology Geologists use a number of field, laboratory, and numerical modeling methods to decipher Earth history and understand the processes that occur on and in the Earth. In typical geological investigations, geologists use primary information related to petrology (the study of rocks), stratigraphy (the study of sedimentary layers), and structural geology (the study of positions of rock units and their deformation). In many cases, geologists also study modern soils, rivers, landscapes, and glaciers; investigate past and current life and biogeochemical pathways, and use geophysical methods to investigate the subsurface.

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Field methods Geological field work varies depending on the task at hand. Typical fieldwork could consist of: • Geological mapping[26] • Structural mapping: the locations of the major rock units and the faults and folds that led to their placement there. • Stratigraphic mapping: the locations of sedimentary facies (lithofacies and biofacies) or the mapping of isopachs of equal thickness of sedimentary rock • Surficial mapping: the locations of soils and surficial deposits • Surveying of topographic features

A standard Brunton Geo com, used commonly by geologists in mapping and surveying

• Creation of topographic maps[27] • Work to understand change across landscapes, including: • Patterns of erosion and deposition • River channel change through migration and avulsion • Hillslope processes • Subsurface mapping through geophysical methods[28] • These methods include: • Shallow seismic surveys • Ground-penetrating radar • Electrical resistivity tomography • They are used for:

A typical USGS field mapping camp in the 1950's

• Hydrocarbon exploration • Finding groundwater • Locating buried archaeological artifacts • High-resolution stratigraphy • Measuring and describing stratigraphic sections on the surface • Well drilling and logging • Biogeochemistry and geomicrobiology[29] • Collecting samples to: • Determine biochemical pathways • Identify new species of organisms. These organisms may help to show: • Identify new chemical compounds

Today, handheld computers with GPS and geographic information systems software are often used in geological field work (digital geologic mapping).

• And to use these discoveries to • Understand early life on Earth and how it functioned and metabolized • Find important compounds for use in pharmaceuticals. • Paleontology: excavation of fossil material • For research into past life and evolution • For museums and education • Collection of samples for geochronology and thermochronology[30] • Glaciology: measurement of characteristics of glaciers and their motion[31]

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Laboratory methods Petrology In addition to the field identification of rocks, petrologists identify rock samples in the laboratory. Two of the primary methods for identifying rocks in the laboratory are through optical microscopy and by using an electron microprobe. In an optical mineralogy analysis, thin sections of rock samples are analyzed through a petrographic microscope, where the minerals can be identified through their different properties in plane-polarized and cross-polarized light, including their birefringence, pleochroism, twinning, and interference properties with a conoscopic lens.[32] In the electron microprobe, individual locations are analyzed for their exact chemical compositions and variation in composition within individual crystals.[33] Stable[34] and radioactive isotope[35] studies provide insight into the geochemical evolution of rock units. Petrologists use fluid inclusion data[36] and perform high temperature and pressure physical experiments[37] to understand the temperatures and pressures at which different mineral phases appear, and how they change through igneous[38] and metamorphic processes. This research can be extrapolated to the field to understand metamorphic processes and the conditions of crystallization of igneous rocks.[39] This work can also help to explain processes that occur within the Earth, such as subduction and magma chamber evolution.

A petrographic microscope, which is a optical microscope fitted with cross-polarizing lenses, a conoscopic lens, and compensators (plates of anisotropic materials; gypsum plates and quartz wedges are common), for crystallographic analysis.

Structural geology

A diagram of an orogenic wedge. The wedge grows through faulting in the interior and along the main basal fault, called the décollement. It builds its shape into a critical taper, in which the angles within the wedge remain the same as failures inside the material balance failures along the décollement. It is analogous to a bulldozer pushing a pile of dirt, where the bulldozer is the overriding plate.

Structural geologists use microscopic analysis of oriented thin sections of geologic samples to observe the fabric within the rocks which gives information about strain within the crystal structure of the rocks. They also plot and combine measurements of geological structures in order to better understand the orientations of faults and folds in order to reconstruct the history of rock deformation in the area. In addition, they perform analog and numerical experiments of rock

deformation in large and small settings. The analysis of structures is often accomplished by plotting the orientations various features onto stereonets. A stereonet is a stereographic projection of a sphere onto a plane, in which planes are projected as lines and lines are projected as points. These can be used to find the locations of fold axes, relationships between several faults, and relationships between other geologic structures. Among the most well-known experiments in structural geology are those involving orogenic wedges, which are zones in which mountains are built along convergent tectonic plate boundaries.[40] In the analog versions of these

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experiments, horizontal layers of sand are pulled along a lower surface into a back stop, which results in realistic-looking patterns of faulting and the growth of a critically tapered (all angles remain the same) orogenic wedge.[41] Numerical models work in the same way as these analog models, though they are often more sophisticated and can include patterns of erosion and uplift in the mountain belt.[42] This helps to show the relationship between erosion and the shape of the mountain range. These studies can also give useful information about pathways for metamorphism through pressure, temperature, space, and time.[43] Stratigraphy In the laboratory, stratigraphers analyze samples of stratigraphic sections that can be returned from the field, such as those from drill cores.[44] Stratigraphers also analyze data from geophysical surveys that show the locations of stratigraphic units in the subsurface.[45] Geophysical data and well logs can be combined to produce a better view of the subsurface, and stratigraphers often use computer programs to do this in three dimensions.[46] Stratigraphers can then use these data to reconstruct ancient processes occurring on the surface of the Earth,[47] interpret past environments, and locate areas for water, coal, and hydrocarbon extraction.

Exploration geologists examining a freshly recovered drill core. Chile, 1994

In the laboratory, biostratigraphers analyze rock samples from outcrop and drill cores for the fossils found in them.[44] These fossils help scientists to date the core and to understand the depositional environment in which the rock units formed. Geochronologists precisely date rocks within the stratigraphic section in order to provide better absolute bounds on the timing and rates of deposition.[48] Magnetic stratigraphers look for signs of magnetic reversals in igneous rock units within the drill cores.[44] Other scientists perform stable isotope studies on the rocks to gain information about past climate.[44]

Planetary geology With the advent of space exploration in the twentieth century, geologists have begun to look at other planetary bodies in the same way as the Earth. This led to the establishment of the field of planetary geology, sometimes known as Astrogeology, in which geologic principles are applied to other bodies of the solar system. Although the Greek-language-origin prefix geo refers to Earth, "geology" is often used in conjunction with the names of other planetary bodies when describing their composition and internal processes: examples are "the geology of Mars" and "Lunar geology". Specialised such as selenology (studies of the Moon), areology (of Mars), etc., are also in use. Surface of Mars as photographed by the Viking 2 Although planetary geologists are interested in all aspects of the lander December 9, 1977. planets, a significant focus is in the search for past or present life on other worlds. This has led to many missions whose purpose (or one of their purposes) is to examine planetary bodies for evidence of life. One of these is the Phoenix lander, which analyzed Martian polar soil for water and chemical and mineralogical constituents related to biological processes.

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Applied geology Economic geology Economic geologists help locate and manage the Earth's natural resources, such as petroleum and coal, as well as mineral resources, which include metals such as iron, copper, and uranium. Mining geology Mining geology consists of the extractions of mineral resources from the Earth. Some resources of economic interests include gemstones, metals, and many minerals such as asbestos, perlite, mica, phosphates, zeolites, clay, pumice, quartz, and silica, as well as elements such as sulfur, chlorine, and helium. Petroleum geology Petroleum geologists study locations of the subsurface of the Earth which can contain extractable hydrocarbons, especially petroleum and natural gas. Because many of these reservoirs are found in sedimentary basins,[49] they study the formation of these basins, as well as their sedimentary and tectonic evolution and the present-day positions of the rock units.

Engineering geology Engineering geology is the application of the geologic principles to engineering practice for the purpose of assuring that the geologic factors affecting the location, design, construction, operation and maintenance of engineering works are properly addressed.

Mud process, a common way to study the lithology when drilling oil wells.

In the field of civil engineering, geological principles and analyses are used in order to ascertain the mechanical principles of the material on which structures are built. This allows tunnels to be built without collapsing, bridges and skyscrapers to be built with sturdy foundations, and buildings to be built that will not settle in clay and mud.[50]

Hydrology and environmental issues Geology and geologic principles can be applied to various environmental problems, such as stream restoration, the restoration of brownfields, and the understanding of the interactions between natural habitat and the geologic environment. Groundwater hydrology, or hydrogeology, is used to locate groundwater,[51] which can often provide a ready supply of uncontaminated water and is especially important in arid regions,[52] and to monitor the spread of contaminants in groundwater wells.[51] [53] Geologists also obtain data through stratigraphy, boreholes, core samples, and ice cores. Ice cores[54] and sediment cores[55] are used to for paleoclimate reconstructions, which tell geologists about past and present temperature, precipitation, and sea level across the globe. These data are our primary source of information on global climate change outside of instrumental data.[56]

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Natural hazards Geologists and geophysicists study natural hazards in order to enact safe building codes and warning systems that are used to prevent loss of property and life.[57] Examples of important natural hazards that are pertinent to geology (as opposed those that are mainly or only pertinent to meteorology) are: • Avalanches • Earthquakes • Floods • Landslides and debris flows • River channel migration and avulsion • Liquefaction • Sinkholes • Subsidence • Tsunamis • Volcanoes

Fields or related disciplines • Earth science • Economic geology

• • • •

• Mining geology • Petroleum geology Engineering geology Environmental geology Geoarchaeology Geochemistry

• • • • • • • • • • • • • • •

• Biogeochemistry • Isotope geochemistry Geochronology Geodetics Geography Geological modelling Geometallurgy Geomicrobiology Geomorphology Geomythology Geophysics Glaciology Historical geology Hydrogeology Meteorology Mineralogy Oceanography

• Marine geology • Paleoclimatology • Paleontology

Rockfall in the Grand Canyon

Geology

• • • • • •

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• Micropaleontology • Palynology Petrology Petrophysics Plate tectonics Sedimentology Seismology Soil science

• Pedology (soil study) • Speleology • Stratigraphy • Biostratigraphy • Chronostratigraphy • Lithostratigraphy • Structural geology • Volcanology

Regional geology By mountain range • • • • •

Geology of the Alps Geology of the Andes Geology of the Appalachians Geology of the Himalaya Geology of the Rocky Mountains

By nations • Geology of Australia • Geology of the Australian Capital Territory • Geology of Tasmania • Geology of Victoria • Geology of the Yilgarn Craton • Geology of China • Geology of Hong Kong • Geology of Europe • • • • •

Geology of Iberia Geology of Iceland Geology of the Netherlands Geology of Norway Geology of Sweden

• Geology of Gotland • Geology of the United Kingdom • Geology of England • Geology of Cheshire • Geology of Cornwall

Geology

82 • Geology of Lizard, Cornwall • Geology of Dorset • Geology of Gloucestershire • Geology of Hampshire • Geology of East Sussex • Geology of Hertfordshire • Geology of Shropshire • Geology of Somerset • Geology of Yorkshire • Geology of Scotland

• Geology of Orkney • Geology of Wales • Geology of Jersey • Geology of Guernsey • Geology of South America • Geology of Bolivia • Geology of Chile • Geology of Colombia • Geology of the Falkland Islands • Geology of India • • • • •

• Geology of Sikkim Geology of Japan Geology of the Philippines Geology of New Zealand Geology of Vietnam Geology of the United States of America • US geology by state: • Geology of Alabama • Geology of Connecticut • Geology of Delaware • Geology of Georgia • Geology of Idaho • Geology of Illinois • Geology of Iowa • Geology of Kansas • Geology of Minnesota • Geology of New Jersey • Geology of Oklahoma • Geology of Pennsylvania • Geology of Tennessee • Geology of Texas • Geology of West Virginia • US Geology by region or feature: • Geology of the Appalachians • Geology of the Pacific Northwest • Geology of the Bryce Canyon area(Utah)

Geology

83 • • • • • • • • • • •

Geology of the Canyonlands area (Utah) Geology of the Capitol Reef area (Utah) Geology of the Death Valley area (California) Geology of the Grand Canyon area (Arizona) Geology of the Grand Teton area (Wyoming) Geology of the Lassen area (California) Geology of Mount Adams (Washington) Geology of Mount Shasta (California) Geology of the Yosemite area (California) Geology of the Zion and Kolob canyons area (Utah) Glacial geology of the Genesee River (New York, Pennsylvania)

By planet • • • •

Geology of Mars Geology of Mercury Geology of the Moon Geology of Venus

Notes [1] Simon Winchester ; (2002). The map that changed the world: William Smith and the birth of modern geology. New York, NY: Perennial. ISBN 0060931809. [2] Fielding H. Garrison wrote in the History of Medicine:

"The Saracens themselves were the originators not only of algebra, chemistry, and geology, but of many of the so-called improvements or refinements of civilization, such as street lamps, window-panes, fireworks, stringed instruments, cultivated fruits, perfumes, spices, etc." [3] Abdus Salam (1984), "Islam and Science". In C. H. Lai (1987), Ideals and Realities: Selected Essays of Abdus Salam, 2nd ed., World Scientific, Singapore, pp. 179–213. [4] Toulmin, S. and Goodfield, J. (1965), ’The Ancestry of science: The Discovery of Time’, Hutchinson & Co., London, p. 64 [5] Winchester, Simon (2001). The Map that Changed the World. HarperCollins Publishers. pp. 25. ISBN 0-06-093180-9. [6] James Hutton: The Founder of Modern Geology (http:/ / www. amnh. org/ education/ resources/ rfl/ web/ essaybooks/ earth/ p_hutton. html), American Museum of Natural History [7] http:/ / www. gutenberg. org/ etext/ 12861 [8] http:/ / www. gutenberg. org/ etext/ 14179 [9] Charles Lyell. (1991). Principles of geology. Chicago: University of Chicago Press. ISBN 9780226497976. [10] England, Philip; Molnar, Peter; Richter, Frank (2007). "John Perry's neglected critique of Kelvin's age for the Earth: A missed opportunity in geodynamics". GSA Today 17: 4. doi:10.1130/GSAT01701A.1. [11] Dalrymple, G.B. (1991). The Age of the Earth. California: Stanford University Press. ISBN 0-8047-1569-6. [12] International Commission on Stratigraphy (http:/ / www. stratigraphy. org/ ) [13] Amelin, Y; Krot, An; Hutcheon, Id; Ulyanov, Aa (Sep 2002). "Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions.". Science 297 (5587): 1678–83. doi:10.1126/science.1073950. ISSN 0036-8075. PMID 12215641. [14] Patterson, C., 1956. “Age of Meteorites and the Earth.” Geochimica et Cosmochimica Acta 10: p. 230-237. [15] G. Brent Dalrymple (1994). The age of the earth. Stanford, Calif.: Stanford Univ. Press. ISBN 0804723311. [16] Olsen, Paul E. (2001). "Steno's Principles of Stratigraphy" (http:/ / rainbow. ldeo. columbia. edu/ courses/ v1001/ steno. html). Dinosaurs and the History of Life. Columbia University. . Retrieved 2009-03-14. [17] Reijer Hooykaas, Natural Law and Divine Miracle: The Principle of Uniformity in Geology, Biology, and Theology (http:/ / books. google. com/ books?id=3TgYAAAAIAAJ& pgis=1), Leiden: EJ Brill, 1963. [18] As recounted in Simon Winchester, The Map that Changed the World (New York: HarperCollins, 2001), pp. 59–91. [19] Tucker, R. D.; Bradley, D. C.; Ver Straeten, C. A.; Harris, A. G.; Ebert, J. R.; McCutcheon, S. R. (1998). "New U–Pb zircon ages and the duration and division of Devonian time". Earth and Planetary Science Letters 158: 175. doi:10.1016/S0012-821X(98)00050-8. [20] Hugh R. Rollinson (1996). Using geochemical data evaluation, presentation, interpretation. Harlow: Longman. ISBN 9780582067011. [21] Gunter Faure. (1998). Principles and applications of geochemistry : a comprehensive textbook for geology students. Upper Saddle River, NJ: Prentice-Hall. ISBN 9780023364501.

Geology [22] H. H. Hess, " History Of Ocean Basins (http:/ / repositories. cdlib. org/ sio/ lib/ 23)" (November 1, 1962). IN: Petrologic studies: a volume in honor of A. F. Buddington. A. E. J. Engel, Harold L. James, and B. F. Leonard, editors. [New York?]: Geological Society of America, 1962. pp. 599–620. [23] Kious, Jacquelyne; Tilling, Robert I. (February 1996). "Developing the Theory" (http:/ / pubs. usgs. gov/ gip/ dynamic/ understanding. html). This Dynamic Earth: The Story of Plate Tectonics. Kiger, Martha, Russel, Jane (Online ed.). Reston, Virginia, USA: United States Geological Survey. ISBN 0-16-048220-8. . Retrieved 13 March 2009. [24] Kious, Jacquelyne; Tilling, Robert I. (February 1996). "Understanding Plate Motions" (http:/ / pubs. usgs. gov/ gip/ dynamic/ understanding. html). This Dynamic Earth: The Story of Plate Tectonics. Kiger, Martha, Russel, Jane (Online ed.). Reston, Virginia, USA: United States Geological Survey. ISBN 0-16-048220-8. . Retrieved 13 March 2009. [25] Origin of continents and oceans. S.l.: Dover Pub. 1999. ISBN 0486617084. [26] Robert R. Compton. (1985). Geology in the field. New York: Wiley. ISBN 0471829021. [27] "USGS Topographic Maps" (http:/ / topomaps. usgs. gov/ ). United States Geological Survey. . Retrieved 2009-04-11. [28] H. Robert Burger, Anne F. Sheehan, Craig H. Jones. (2006). Introduction to applied geophysics : exploring the shallow subsurface. New York: W.W. Norton. ISBN 0393926370. [29] ed. by Wolfgang E. Krumbein (1978). Environmental biogeochemistry and geomicrobiology. Ann Arbor, Mich.: Ann Arbor Science Publ.. ISBN 0250402181. [30] Ian McDougall, T. Mark Harrison. (1999). Geochronology and thermochronology by the ♯°Ar/©Ar method. New York: Oxford University Press. ISBN 0195109201. [31] Bryn Hubbard, Neil Glasser. (2005). Field techniques in glaciology and glacial geomorphology. Chichester, England: J. Wiley. ISBN 0470844264. [32] William D. Nesse. (1991). Introduction to optical mineralogy. New York: Oxford University Press. ISBN 0195060245. [33] Morton, ANDREW C. (1985). "A new approach to provenance studies: electron microprobe analysis of detrital garnets from Middle Jurassic sandstones of the northern North Sea". Sedimentology 32: 553. doi:10.1111/j.1365-3091.1985.tb00470.x. [34] Zheng, Y (2003). "Stable isotope geochemistry of ultrahigh pressure metamorphic rocks from the Dabie–Sulu orogen in China: implications for geodynamics and fluid regime". Earth-Science Reviews 62: 105. doi:10.1016/S0012-8252(02)00133-2. [35] Condomines, M; Tanguy, J; Michaud, V (1995). "Magma dynamics at Mt Etna: Constraints from U-Th-Ra-Pb radioactive disequilibria and Sr isotopes in historical lavas". Earth and Planetary Science Letters 132: 25. doi:10.1016/0012-821X(95)00052-E. [36] T.J. Shepherd, A.H. Rankin, D.H.M. Alderton. (1985). A practical guide to fluid inclusion studies. Glasgow: Blackie. ISBN 0412006014. [37] Sack, Richard O.; Walker, David; Carmichael, Ian S. E. (1987). "Experimental petrology of alkalic lavas: constraints on cotectics of multiple saturation in natural basic liquids". Contributions to Mineralogy and Petrology 96: 1. doi:10.1007/BF00375521. [38] Alexander R. McBirney. (2007). Igneous petrology. Boston: Jones and Bartlett Publishers. ISBN 9780763734480. [39] Frank S. Spear (1995). Metamorphic phase equilibria and pressure-temperature-time paths. Washington, DC: Mineralogical Soc. of America. ISBN 9780939950348. [40] Dahlen, F A (1990). "Critical Taper Model of Fold-And-Thrust Belts and Accretionary Wedges". Annual Review of Earth and Planetary Sciences 18: 55. doi:10.1146/annurev.ea.18.050190.000415. [41] Gutscher, M (1998). "Material transfer in accretionary wedges from analysis of a systematic series of analog experiments". Journal of Structural Geology 20: 407. doi:10.1016/S0191-8141(97)00096-5. [42] Koons, P O (1995). "Modeling the Topographic Evolution of Collisional Belts". Annual Review of Earth and Planetary Sciences 23: 375. doi:10.1146/annurev.ea.23.050195.002111. [43] Dahlen, F. A., Suppe, J. & Davis, D. J. geophys. Res. 89, 10087−10101 (1983). [44] Hodell, David A.; Benson, Richard H.; Kent, Dennis V.; Boersma, Anne; Rakic-El Bied, Kruna (1994). "Magnetostratigraphic, Biostratigraphic, and Stable Isotope Stratigraphy of an Upper Miocene Drill Core from the Salé Briqueterie (Northwestern Morocco): A High-Resolution Chronology for the Messinian Stage". Paleoceanography 9: 835. doi:10.1029/94PA01838. [45] edited by A.W. Bally. (1987). Atlas of seismic stratigraphy. Tulsa, Okla., U.S.A.: American Association of Petroleum Geologists. ISBN 0891810331. [46] Fernández, O.; Muñoz, J. A.; Arbués, P.; Falivene, O.; Marzo, M. (2004). "Three-dimensional reconstruction of geological surfaces: An example of growth strata and turbidite systems from the Ainsa basin (Pyrenees, Spain)". AAPG Bulletin 88: 1049. doi:10.1306/02260403062. [47] Poulsen, Chris J.; Flemings, Peter B.; Robinson, Ruth A. J.; Metzger, John M. (1998). "Three-dimensional stratigraphic evolution of the Miocene Baltimore Canyon region: Implications for eustatic interpretations and the systems tract model". Geological Society of America Bulletin 110: 1105. doi:10.1130/0016-7606(1998)110<1105:TDSEOT>2.3.CO;2. [48] Toscano, M (1999). "Submerged Late Pleistocene reefs on the tectonically-stable S.E. Florida margin: high-precision geochronology, stratigraphy, resolution of Substage 5a sea-level elevation, and orbital forcing.". Quaternary Science Reviews 18: 753. doi:10.1016/S0277-3791(98)00077-8. [49] Richard C. Selley. (1998). Elements of petroleum geology. San Diego: Academic Press. ISBN 0-12-636370-6. [50] Braja M. Das. (2006). Principles of geotechnical engineering. England: THOMSON LEARNING (KY). ISBN 0534551440. [51] Hamilton, Pixie A.; Helsel, Dennis R. (1995). "Effects of Agriculture on Ground-Water Quality in Five Regions of the United States". Ground Water 33: 217. doi:10.1111/j.1745-6584.1995.tb00276.x. [52] Seckler, David; Barker, Randolph; Amarasinghe, Upali (1999). "Water Scarcity in the Twenty-first Century". International Journal of Water Resources Development 15: 29. doi:10.1080/07900629948916.

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Geology [53] Welch, Alan H.; Lico, Michael S.; Hughes, Jennifer L. (1988). "Arsenic in Ground Water of the Western United States". Ground Water 26: 333. doi:10.1111/j.1745-6584.1988.tb00397.x. [54] Barnola, J. M.; Raynaud, D.; Korotkevich, Y. S.; Lorius, C. (1987). "Vostok ice core provides 160,000-year record of atmospheric CO2". Nature 329: 408. doi:10.1038/329408a0. [55] Colman, S.M.; Jones, G.A.; Forester, R.M.; Foster, D.S. (1990). "Holocene paleoclimatic evidence and sedimentation rates from a core in southwestern Lake Michigan". Journal of Paleolimnology 4. doi:10.1007/BF00239699. [56] Jones, P. D. (2004). "Climate over past millennia". Reviews of Geophysics 42: RG2002. doi:10.1029/2003RG000143. [57] USGS Natural Hazards Gateway (http:/ / www. usgs. gov/ hazards/ )

External links • GeologyForum.org (http://geologyforum.org) an online community for fans of everything Geologic! • James Hutton's Theory of the Earth (http://records.viu.ca/~johnstoi/essays/Hutton.htm) • Charles Lyell's Elements of Geology (http://books.google.com/books?id=-AcKAAAAIAAJ& printsec=frontcover&dq=Charles+Lyell&ei=YMOLSa_GE4uiyATW_Zy6BQ&client=firefox-a#PPR5,M1) • Charles Lyell's Principles of Geology, or the Modern Changes of the Earth and its Inhabitants, Considered as Illustrative of Geology (http://books.google.com/books?id=O2YNAAAAYAAJ&printsec=frontcover& dq=Charles+Lyell&ei=YMOLSa_GE4uiyATW_Zy6BQ&client=firefox-a#PPR3,M1) • American Geophysical Union (http://www.agu.org) • • • •

European Geosciences Union (http://www.egu.eu/) Geological Society of America (http://www.geosociety.org) Earth Science News, Maps, Dictionary, Articles, Jobs (http://geology.com) Geological Society of London (http://www.geolsoc.org.uk)

Soil science Soil science is the study of soil as a natural resource on the surface of the earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils.[1] Sometimes which refer to branches of soil science, such as pedology (formation, chemistry, morphology and classification of soil) and edaphology (influence of soil on organisms, especially plants), are used as if synonymous with soil science. The diversity of names associated with this discipline is related to the various associations concerned. Indeed, engineers, agronomists, chemists, geologists, geographers, ecologists, biologists, microbiologists, sylviculturists, sanitarians, archaeologists, and specialists in regional planning, all contribute to further knowledge of soils and the advancement of the soil sciences.

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86

Fields of study Soil occupies the pedosphere, one of Earth's spheres that the geosciences use to organize the Earth conceptually. This is the conceptual perspective of pedology and edaphology, the two main branches of soil science. Pedology is the study of soil in its natural setting. Edaphology is the study of soil in relation to soil-dependent uses. Both branches apply a combination of soil physics, soil chemistry, and soil biology. Due to the numerous interactions between the biosphere, atmosphere and hydrosphere that are hosted within the pedosphere, more integrated, less soil-centric concepts are also valuable. Many concepts essential to understanding soil come from individuals not identifiable strictly as soil scientists. This highlights the interdisciplinary nature of soil concepts.

Research Dependence on and curiosity about soil, exploring the diversity and dynamic of this resource continues to yield fresh discoveries and insights. New avenues of soil research are compelled by a need to understand soil in the context of climate change,[2] greenhouse gases,[3] [4] and carbon sequestration.[5] Interest in maintaining the planet's biodiversity and in exploring past cultures has also stimulated renewed interest in achieving a more refined understanding of soil.

Mapping Most empirical knowledge of soil in nature comes from soil survey efforts. Soil survey, or soil mapping, is the process of determining the soil types or other properties of the soil cover over a landscape, and mapping them for others to understand and use. It relies heavily on distinguishing the individual influences of the five classic soil forming factors. This effort draws upon geomorphology, physical geography, and analysis of vegetation and land-use patterns. Primary data for the soil survey are acquired by field sampling and ed by remote sensing.

Sample of an aerial photo from a published soil survey

Soil science

Classification As of 2006, the World Reference Base for Soil Resources, via its Land & Water Development division, is the pre-eminent soil classification system. It replaces the previous FAO soil classification. The WRB borrows from modern soil classification concepts, including USDA soil taxonomy. The classification is based mainly on soil morphology as an expression pedogenesis. A major difference with USDA soil taxonomy is that soil climate is not part of the system, except insofar as climate influences soil profile characteristics. Map of global soil regions from the USDA Many other classification schemes exist, including vernacular systems. The structure in vernacular systems are either nominal, giving unique names to soils or landscapes, or descriptive, naming soils by their characteristics such as red, hot, fat, or sandy. Soils are distinguished by obvious characteristics, such as physical appearance (e.g., color, texture, landscape position), performance (e.g., production capability, flooding), and accompanying vegetation.[6] A vernacular distinction familiar to many is classifying texture as heavy or light. Light soil content and better structure, take less effort to turn and cultivate. Contrary to popular belief, light soils do not weigh less than heavy soils on an air dry basis nor do they have more porosity.

History Vasily Dokuchaev, a Russian geologist, geographer and early soil scientist, is credited with identifying soil as a resource whose distinctness and complexity deserved to be separated conceptually from geology and crop production and treated as a whole. Previously, soil had been considered a product of chemical transformations of rocks, a dead substrate from which plants derive nutritious elements. Soil and bedrock were in fact equated. Dokuchaev considers the soil as a natural body having its own genesis and its own history of development, a body with complex and multiform processes taking place within it. The soil is considered as different from bedrock. The latter becomes soil under the influence of a series of soil-formation factors (climate, vegetation, country, relief and age). According to him, soil should be called the "daily" or outward horizons of rocks regardless of the type; they are changed naturally by the common effect of water, air and various kinds of living and dead organisms.[7] A 1914 encyclopedic definition: "the different forms of earth on the surface of the rocks, formed by the breaking down or weathering of rocks".[8] serves to illustrate the historic view of soil which persisted from the 19th century. Dokuchaev's late 19th century soil concept developed in the 20th century to one of soil as earthy material that has been altered by living processes.[9] A corollary concept is that soil without a living component is simply a part of earth's outer layer. Further refinement of the soil concept is occurring in view of an appreciation of energy transport and transformation within soil. The term is popularly applied to the material on the surface of the Earth's moon and Mars, a usage acceptable within a portion of the scientific community. Accurate to this modern understanding of soil is Nikiforoff's 1959 definition of soil as the "excited skin of the sub aerial part of the earth's crust".[10]

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Soil science

Areas of practice Academically, soil scientists tend to be drawn to one of five areas of specialization: microbiology, pedology, edaphology, physics or chemistry. Yet the work specifics are very much dictated by the challenges facing our civilization's desire to sustain the land that s it, and the distinctions between the sub-disciplines of soil science often blur in the process. Soil science professionals commonly stay current in soil chemistry, soil physics, soil microbiology, pedology, and applied soil science in related disciplines One interesting effort drawing in soil scientists in the USA as of 2004 is the Soil Quality Initiative. Central to the Soil Quality Initiative is developing indices of soil health and then monitoring them in a way that gives us long term (decade-to-decade) on our performance as stewards of the planet. The effort includes understanding the functions of soil microbiotic crusts and exploring the potential to sequester atmospheric carbon in soil organic matter. The concept of soil quality, however, has not been without its share of controversy and criticism, including critiques by Nobel Laureate Norman Borlaug and World Food Prize Winner Pedro Sanchez. A more traditional role for soil scientists has been to map soils. Most every area in the United States now has a published soil survey, which includes interpretive tables as to how soil properties or limit activities and uses. An internationally accepted soil taxonomy allows uniform communication of soil characteristics and functions. National and international soil survey efforts have given the profession unique insights into landscape scale functions. The landscape functions that soil scientists are called upon to address in the field seem to fall roughly into six areas: • Land-based treatment of wastes • Septic system • Manure • Municipal biosolids • Food and fiber processing waste • Identification and protection of environmentally critical areas • Sensitive and unstable soils • Wetlands • Unique soil situations that valuable habitat, and ecosystem diversity • Management for optimum land productivity • Silviculture • Agronomy • Nutrient management • Water management • Native vegetation • Grazing • Management for optimum water quality • Stormwater management • Sediment and erosion control • Remediation and restoration of damaged lands • Mine reclamation • Flood and storm damage • Contamination • Sustainability of desired uses • Soil conservation There are also practical applications of soil science that might not be apparent from looking at a published soil survey.

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Soil science • Radiometric dating: specifically a knowledge of local pedology is used to date prior activity at the site • Stratification (archeology) where soil formation processes and preservative qualities can inform the study of archaeological sites • Geological phenomena • Landslides • Active faults • Altering soils to achieve new uses • Vitrification to contain radioactive wastes • Enhancing soil microbial capabilities in degrading contaminants (bioremediation). • Carbon sequestration • Environmental soil science • Pedology • Soil genesis • Pedometrics • Soil morphology • Soil micromorphology • Soil classification • USDA soil taxonomy • Soil biology • Soil microbiology • Soil chemistry • Soil biochemistry • Soil mineralogy • Soil physics • Pedotransfer function • Soil mechanics and engineering • Soil hydrology, hydropedology

Fields of application in soil science • • • • • • • •

Soil survey Soil management Standard methods of analysis Soil fertility / Nutrient management Ecosystem studies Climate change Watershed and wetland studies Pedotransfer function

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Related disciplines • Agricultural sciences • Agrophysics science • Irrigation management • Anthropology • archaeological stratigraphy • Environmental science • Landscape ecology • Geography • Physical geography • Geology • Biogeochemistry • Geomicrobiology • Geomorphology • Hydrology • Hydrogeology • Waste management • Wetland science

Degree programs North America • • • •

Michigan State University (Associates, B.S, M.S., and Ph.D. [11]) Purdue University (BS [12], M.S. and Ph.D. [13]) University of Kentucky (BS [14], MS [15], Ph.D [16]) University of Wisconsin - Madison (BS, MS, and Ph.D [17])

Europe • St. Petersburg State University, Bachelor and Master degrees

References [1] Jackson, J. A. (1997). Glossary of Geology (4. ed.). Alexandria, Virginia: American Geological Institute. p 604. ISBN 0922152349 [2] Pielke, Roger(December 12, 2005) Is Soil an Important Component of the Climate System? (http:/ / climatesci. atmos. colostate. edu/ 2005/ 12/ 19/ is-soil-an-important-component-of-the-climate-system/ ) The Climate Science Weblog. Url last accessed 2006-04-19 [3] "Glomalin -- Summary" (http:/ / web. archive. org/ web/ 20070708192258/ http:/ / www. co2science. org/ scripts/ CO2ScienceB2C/ subject/ g/ summaries/ glomalin. jsp). Archived from the original (http:/ / www. co2science. org/ scripts/ CO2ScienceB2C/ subject/ g/ summaries/ glomalin. jsp) on 2007-07-08. . Last updated 25 January 2006. CO2 Science. Url last accessed 2006-04-19 [4] "Soil (stability) -- Summary" (http:/ / web. archive. org/ web/ 20070225230420/ http:/ / www. co2science. org/ scripts/ CO2ScienceB2C/ subject/ s/ summaries/ soilstability. jsp). Archived from the original (http:/ / www. co2science. org/ scripts/ CO2ScienceB2C/ subject/ s/ summaries/ soilstability. jsp) on 2007-02-25. .. CO2 Science. URL last accessed 2006-04-19 [5] "Soil Carbon Sequestration" (http:/ / web. archive. org/ web/ 20070708192202/ http:/ / www. co2science. org/ scripts/ CO2ScienceB2C/ subject/ c/ carbonsoils. jsp). Archived from the original (http:/ / www. co2science. org/ scripts/ CO2ScienceB2C/ subject/ c/ carbonsoils. jsp) on 2007-07-08. .. CO2 Science. Url last accessed 2006-04-19 [6] Vernacular Systems (http:/ / forages. oregonstate. edu/ is/ ssis/ main. cfm?PageID=168) Url last accessed on 2006-04-18 [7] Krasilnikov, N.A. (1958) Soil Microorganisms and Higher Plants (http:/ / www. soilandhealth. org/ 01aglibrary/ 010112Krasil/ 010112krasil. intro. html) [8] "Soils" (http:/ / web. archive. org/ web/ 20080527040509/ http:/ / en. wikisource. org/ wiki/ The_New_Student's_Reference_Work/ 4-0310). The New Student's Reference Work. F. E. Compton and Company. 1914. Archived from the original (http:/ / en. wikisource. org/ wiki/

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Soil science The_New_Student's_Reference_Work/ 4-0310) on 2008-05-27. . Retrieved 2008-07-08. [9] Buol, S. W.; Hole, F. D. and McCracken, R. J. (1973). Soil Genesis and Classification (First ed.). Ames, IA: Iowa State University Press. ISBN 978-0-8138-1460-5.. [10] C. C. Nikiforoff (1959). "Reappraisal of the soil: Pedogenesis consists of transactions in matter and energy between the soil and its surroundings". Science 129 (3343): 186–196. doi:10.1126/science.129.3343.186. PMID 17808687. [11] http:/ / www. css. msu. edu/ FutureStudents. cfm [12] http:/ / www. ag. purdue. edu/ agry/ UndergraduateProgram/ Pages/ default. aspx [13] http:/ / www. ag. purdue. edu/ agry/ GraduateProgram/ Pages/ default. aspx [14] http:/ / www. ca. uky. edu/ Students/ welcome/ plant_soil_science. asp [15] http:/ / www. ca. uky. edu/ pss/ index. php?p=584 [16] http:/ / www. ca. uky. edu/ pss/ index. php?p=587 [17] http:/ / www. soils. wisc. edu

• Soil Survey Staff (1993). Soil Survey: Early Concepts of Soil. (http://soils.usda.gov/technical/manual/ contents/chapter1.html) (html) Soil Survey Manual USDA Handbook 18, Soil Conservation Service. U.S. Department of Agriculture. URL accessed on 2004-11-30.

External links • United States Department of Agriculture Natural Resources Conservation Service - Information on US Soils (http://soils.usda.gov) • • • • • • •

Certified Professional Soil Scientist (https://www.soils.org/certifications/ss-sc) Soil-Science.info (http://soil-science.info/) ISRIC - World Soil Information (http://www.isric.org/) IPSS - Institute of Professional Soil Scientists (http://www.soilscientist.org/) BSSS - British Society of Soil Science (http://www.soils.org.uk/) SSSA - Soil Science Society of America (http://www.soils.org/) National Soil Resources Institute (http://www.cranfield.ac.uk/sas/nsri)

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Oceanography

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Oceanography Oceanography (compound of the Greek words ωκεανός meaning "ocean" and γράφω meaning "to write"), also called oceanology or marine science, is the branch of Earth science that studies the ocean. It covers a wide range of topics, including marine organisms and ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamics; plate tectonics and the geology of the sea floor; and fluxes of various chemical substances and physical properties within the ocean and across its Thermohaline circulation boundaries. These diverse topics reflect multiple disciplines that oceanographers blend to further knowledge of the world ocean and understanding of processes within it: biology, chemistry, geology, meteorology, and physics as well as geography.

History Humans first acquired knowledge of the waves and currents of the seas and oceans in pre-historic times. Observations on tides are recorded by Aristotle and Strabo. Early modern exploration of the oceans was primarily for cartography and mainly limited to its surfaces and of the creatures that fishermen brought up in nets, though depth soundings by lead line were taken. Although Juan Ponce de León in 1513 first identified the Gulf Stream, and the current was well-known to mariners, Benjamin Franklin made the first scientific study of it and gave it its name. Franklin measured water temperatures during several Atlantic crossings and correctly explained the Gulf Stream's cause. Franklin and Timothy Folger printed the first map of the Gulf Stream in 1769-1770.[1] [2]

Map of the Gulf Stream by Benjamin Franklin, 1769-1770. Courtesy of the NOAA Photo Library.

When Louis Antoine de Bougainville, who voyaged between 1766 and 1769, and James Cook, who voyaged from 1768 to 1779, carried out their explorations in the South Pacific, information on the oceans themselves formed part of the reports. James Rennell wrote the first scientific textbooks about currents in the Atlantic and Indian oceans during the late 18th and at the beginning of 19th century. Sir James Clark Ross took the first modern sounding in deep sea in 1840, and Charles Darwin published a paper on reefs and the formation of atolls as a result of the second voyage of HMS Beagle in 1831-6. Robert FitzRoy published a report in four volumes of the three voyages of the Beagle. In 1841–1842 Edward Forbes undertook dredging in the Aegean Sea that founded marine ecology. As first superintendent of the United States Naval Observatory (1842–1861) Matthew Fontaine Maury devoted his time to the study of marine meteorology, navigation, and charting prevailing winds and currents. His Physical Geography of the Sea, 1855 was the first textbook of oceanography. Many nations sent oceanographic observations to Maury at the Naval Observatory, where he and his colleagues evaluated the information and gave the results

Oceanography worldwide distribution.[3] The steep slope beyond the continental shelves was discovered in 1849. The first successful laying of transatlantic telegraph cable in August 1858 confirmed the presence of an underwater "telegraphic plateau" mid-ocean ridge. After the middle of the 19th century, scientific societies were processing a flood of new terrestrial botanical and zoological information. In 1871, under the recommendations of the Royal Society of London, the British government sponsored an expedition to explore world's oceans and conduct scientific investigations. Under that sponsorship the Scots Charles Wyville Thompson and Sir John Murray launched the Challenger expedition (1872–1876). The results of this were published in 50 volumes covering biological, physical and geological aspects. 4417 new species were discovered. Other European and American nations also sent out scientific expeditions (as did private individuals and institutions). The first purpose built oceanographic ship, the "Albatros" was built in 1882. The four-month 1910 North Atlantic expedition headed by Sir John Murray and Johan Hjort was at that time the most ambitious research oceanographic and marine zoological project ever, and led to the classic 1912 book The Depths of the Ocean. Oceanographic institutes dedicated to the study of oceanography were founded. In the United States, these included the Scripps Institution of Oceanography in 1892, Woods Hole Oceanographic Institution in 1930, Virginia Institute of Marine Science in 1938, Lamont-Doherty Earth Observatory at Columbia University, and the School of Oceanography at University of Washington. In Britain, there is a major research institution: National Oceanography Centre, Southampton which is the successor to the Institute of Oceanography. In Australia, CSIRO Marine and Atmospheric Research, known as CMAR, is a leading center. In 1921 the International Hydrographic Bureau (IHB) was formed in Monaco. In 1893, Fridtjof Nansen allowed his ship "Fram" to be frozen in the Arctic ice. As a result he was able to obtain oceanographic data as well as meteorological and astronomical data. The first international organization of oceanography was created in 1902 as the International Council for the Exploration of the Sea. The first acoustic measurement of sea depth was made in 1914. Between 1925 and 1927 the "Meteor" expedition gathered 70,000 ocean depth measurements using an echo sounder, surveying the Mid atlantic ridge. The Great Global Ocean currents (1911) Rift, running along the Mid Atlantic Ridge, was discovered by Maurice Ewing and Bruce Heezen in 1953 while the mountain range under the Arctic was found in 1954 by the Arctic Institute of the USSR. The theory of seafloor spreading was developed in 1960 by Harry Hammond Hess. The Ocean Drilling Project started in 1966. Deep sea vents were discovered in 1977 by John Corlis and Robert Ballard in the submersible "Alvin". In the 1950s, Auguste Piccard invented the bathyscaphe and used the "Trieste" to investigate the ocean's depths. The nuclear submarine Nautilus made the first journey under the ice to the North Pole in 1958. In 1962 there was the first deployment of FLIP (Floating Instrument Platform), a 355 foot spar buoy. Then, in 1966, the U.S. Congress created a National Council for Marine Resources and Engineering Development. NOAA was put in charge of exploring and studying all aspects of Oceanography in the USA. It also enabled the National Science Foundation to award Sea Grant College funding to multi-disciplinary researchers in the field of oceanography.[4] [5] From the 1970s, there has been much emphasis on the application of large scale computers to oceanography to allow numerical predictions of ocean conditions and as a part of overall environmental change prediction. An oceanographic buoy array was established in the Pacific to allow prediction of El Niño events.

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1990 saw the start of the World Ocean Circulation Experiment (WOCE) which continued until 2002. Geosat seafloor mapping data became available in 1995. In 1942, Sverdrup and Fleming published "The Ocean" which was a major landmark. "The Sea" (in three volumes covering physical oceanography, seawater and geology) edited by M.N. Hill was published in 1962 while the "Encyclopedia of Oceanography" by Rhodes Fairbridge was published in 1966.

Connection to the atmosphere The study of the oceans is linked to understanding global climate changes, potential global warming and related biosphere concerns. The atmosphere and ocean are linked because of evaporation and precipitation as well as thermal flux (and solar insolation). Wind stress is a major driver of ocean currents while the ocean is a sink for atmospheric carbon dioxide. Our planet is invested with two great oceans; one visible, the other invisible; one underfoot, the other overhead; one entirely envelopes it, the other covers about two thirds of its surface. —Matthew F. Maury, The Physical Geography of the Seas and Its Meteorology (1855)

Branches The study of oceanography is divided into branches: • Biological oceanography, or marine biology, is the study of the plants, animals and microbes of the oceans and their ecological interaction with the ocean; • Chemical oceanography, or marine chemistry, is the study of the chemistry of the ocean and its chemical interaction with the atmosphere; • Geological oceanography, or marine geology, is the study of the geology of the ocean floor including plate tectonics; • Physical oceanography, or marine physics, studies the ocean's physical attributes including temperature-salinity structure, mixing, waves, internal waves, surface tides, internal tides, and currents. Of particular interest is the behavior of sound (acoustical oceanography), light (optical oceanography) and radio waves in the ocean.

Oceanographic frontal systems on the Southern Hemisphere

These branches reflect the fact that many oceanographers are first trained in the exact sciences or mathematics and then focus on applying their interdisciplinary knowledge, skills and abilities to oceanography.[6] Data derived from the work of Oceanographers is used in marine engineering, in the design and building of oil platforms, ships, harbours, and other structures that allow us to use the ocean safely.[7] Oceanographic data management is the discipline ensuring that oceanographic data both past and present are available to researchers.

Oceanography

Related disciplines • • • • • • • • • • • •

Biogeochemistry Biogeography Coastal geography Environmental science Geophysics Glaciology Hydrography Hydrology Limnology Meteorology Ocean dynamics Physical geography

See also • American Practical Navigator • • • • • • • • • • • • • • • • • • • •

Anoxic event – Anoxic sea water Argo (oceanography) Atlantic Oceanographic and Meteorological Laboratory (AOML) (in the US) Bathymetric chart Ecological Forecasting Fleet Numerical Oceanography Center (USA) Freak wave List of submarine topographical features List of Russian oceanographers Marine archaeology Marine current power Marine engineering Ocean colonization Ocean engineering Oceanographic Museum – Monaco Oceans Act of 2000 Pollution Sea – contains list of world's seas Sea level Sea level rise

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References [1] [2] [3] [4] [5] [6]

1785: Benjamin Franklin's 'Sundry Maritime Observations' (http:/ / oceanexplorer. noaa. gov/ library/ readings/ gulf/ gulf. html) Wilkinson, Jerry. History of the Gulf Stream (http:/ / www. keyshistory. org/ gulfstream. html) January 01, 2008. Williams, s L. Matthew Fontaine Maury, Scientist of the Sea. (1969) ISBN 0-8135-0433-3. NOAA National Sea Grant Office (NSGO). (http:/ / www. seagrant. noaa. gov/ ) Topic: Sea Grant Colleges. (http:/ / www. factbites. com/ topics/ Sea-Grant-Colleges) Impact from the Deep (http:/ / www. sciamdigital. com/ index. cfm?fa=Products. ViewIssuePreview& ARTICLEID_CHAR=8E5BF2D2-2B35-221B-6CC622E027B244CC); October 2006; Scientific American Magazine; by Peter D. Ward; 8 Page(s) [7] Tom Garrison. "Oceanography: An Invitation to Marine Science" 5th edition. Thomson, 2005. Page 4.

Further reading • Hamblin, Jacob Darwin (2005) Oceanographers and the Cold War: Disciples of Marine Science (http://books. google.co.nz/books?id=6jrUK226eRgC&dq=Hamblin+"Oceanographers+and+the+Cold+War"&pg=PP1& ots=0Us_ku7jpm&sig=bck0Mb9eT9Ih-RmDrRIs_nWzzg0&hl=en&sa=X&oi=book_result&resnum=1& ct=result). University of Washington Press. ISBN 978-0295984827 • Steele, J., K. Turekian and S. Thorpe. (2001). Encyclopedia of Ocean Sciences. San Diego: Academic Press. (6 vols.) ISBN 0-12-227430-X • Sverdrup, Keith A., Duxbury, Alyn C., Duxbury, Alison B. (2006). Fundamentals of Oceanography, McGraw-Hill, ISBN 0072826789.

External links • NASA Jet Propulsion Laboratory - Physical Oceanography Distributed Active Archive Center (PO.DAAC) (http:/ /podaac.jpl.nasa.gov/). A data center responsible for archiving and distributing data about the physical state of the ocean. • Woods Hole Oceanographic Institution (WHOI) (http://www.whoi.edu). The world's largest private, non-profit ocean research, engineering and education organization. • British Oceanographic Data Centre (http://www.bodc.ac.uk/). A source of oceanographic data and information. • NOAA Ocean and Weather Data Navigator (http://dapper.pmel.noaa.gov/dchart/). Plot and ocean data. • Freeview Video 'Voyage to the Bottom of the Deep Deep Sea' Oceanography Programme (http://www.vega. org.uk/video/programme/10) by the Vega Science Trust and the BBC/Open University.

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Geography Geography (from Greek γεωγραφία geographia, lit. "earth describe-write"[1] ) is the science that deals with the study of the Earth and its lands, features, inhabitants, and phenomena.[2] A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes (276-194 BC). Four historical traditions in geographical research are the spatial analysis of natural and human Map of the Earth phenomena (geography as a study of distribution), area studies (places and regions), study of man-land relationship, and research in earth sciences.[3] Nonetheless, modern geography is an all-encoming discipline that foremost seeks to understand the Earth and all of its human and natural complexities—not merely where objects are, but how they have changed and come to be. Geography has been called 'the world discipline'.[4] As "the bridge between the human and physical sciences," geography is divided into two main branches—human geography and physical geography.[5] [6]

Introduction Traditionally, geographers have been viewed the same way as cartographers and people who study place names and numbers. Although many geographers are trained in toponymy and cartology, this is not their main preoccupation. Geographers study the spatial and temporal distribution of phenomena, processes and features as well as the interaction of humans and their environment.[7] As space and place affect a variety of topics such as economics, health, climate, plants and animals, geography is highly interdisciplinary.

“

...mere names of places...are not geography...know by heart a whole gazetteer full of them would not, in itself, constitute anyone a geographer. Geography has higher aims than this: it seeks to classify phenomena (alike of the natural and of the political world, in so far as it treats of the latter), to compare, to generalize, to ascend from effects to causes, and, in doing so, to trace out the great laws of nature and to mark their influences upon man. This is 'a description of the world'—that is Geography. In a word Geography is a Science—a thing not of mere names [8] but of argument and reason, of cause and effect.

”

— William Hughes, 1863

Geography as a discipline can be split broadly into two main subsidiary fields: human geography and physical geography. The former focuses largely on the built environment and how space is created, viewed and managed by humans as well as the influence humans have on the space they occupy. The latter examines the natural environment and how the climate, vegetation & life, soil, water, and landforms are produced and interact.[9] As a result of the two subfields using different approaches a third field has emerged, which is environmental geography. Environmental geography combines physical and human geography and looks at the interactions between the environment and humans.[7]

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Branches Physical geography Physical geography (or physiography) focuses on geography as an Earth science. It aims to understand the physical lithosphere, hydrosphere, atmosphere, pedosphere, and global flora and fauna patterns (biosphere). Physical geography can be divided into the following broad categories:

Biogeography

Climatology & paleoclimatology Coastal geography Env. geog. & management

Geodesy

Geomorphology

Glaciology

Hydrology & Hydrography

Landscape ecology

Oceanography

Pedology

Palaeogeography

Quaternary science

Human geography Human geography is a branch of geography that focuses on the study of patterns and processes that shape human interaction with various environments. It encomes human, political, cultural, social, and economic aspects. While the major focus of human geography is not the physical landscape of the Earth (see physical geography), it is hardly possible to discuss human geography without referring to the physical landscape on which human activities are being played out, and environmental geography is emerging as a link between the two. Human geography can be divided into many broad categories, such as:

Cultural geography

Development geography

Economic geography

Health geography

Historical & Time geog. Political geog. & Geopolitics Pop. geog. or Demography Religion geography

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Social geography

Transportation geography

Tourism geography

Urban geography

Various approaches to the study of human geography have also arisen through time and include: • • • •

Behavioral geography Feminist geography Culture theory Geosophy

Environmental geography Environmental geography is the branch of geography that describes the spatial aspects of interactions between humans and the natural world. It requires an understanding of the traditional aspects of physical and human geography, as well as the ways in which human societies conceptualize the environment. Environmental geography has emerged as a bridge between human and physical geography as a result of the increasing specialisation of the two sub-fields. Furthermore, as human relationship with the environment has changed as a result of globalization and technological change a new approach was needed to understand the changing and dynamic relationship. Examples of areas of research in environmental geography include emergency management, environmental management, sustainability, and political ecology.

Geomatics Geomatics is a branch of geography that has emerged since the quantitative revolution in geography in the mid 1950s. Geomatics involves the use of traditional spatial techniques used in cartography and topography and their application to computers. Geomatics has become a widespread field with many other disciplines using techniques such as GIS and remote sensing. Geomatics has also led to a revitalization of some geography departments especially in Northern America where the subject had a declining status during the 1950s. Geomatics encomes a large area of fields involved with spatial analysis, such as Cartography, Geographic information systems (GIS), Remote sensing, and Global positioning systems (GPS).

Digital Elevation Model (DEM)

Geography

Regional geography Regional geography is a branch of geography that studies the regions of all sizes across the Earth. It has a prevailing descriptive character. The main aim is to understand or define the uniqueness or character of a particular region which consists of natural as well as human elements. Attention is paid also to regionalization which covers the proper techniques of space delimitation into regions. Regional geography is also considered as a certain approach to study in geographical sciences (similar to quantitative or critical geographies, for more information see History of geography).

Related fields • Urban planning, regional planning and spatial planning: use the science of geography to assist in determining how to develop (or not develop) the land to meet particular criteria, such as safety, beauty, economic opportunities, the preservation of the built or natural heritage, and so on. The planning of towns, cities, and rural areas may be seen as applied geography. • Regional science: In the 1950s the regional science movement led by Walter Isard arose, to provide a more quantitative and analytical base to geographical questions, in contrast to the descriptive tendencies of traditional geography programs. Regional science comprises the body of knowledge in which the spatial dimension plays a fundamental role, such as regional economics, resource management, location theory, urban and regional planning, transport and communication, human geography, population distribution, landscape ecology, and environmental quality. • Interplanetary Sciences: While the discipline of geography is normally concerned with the Earth, the term can also be informally used to describe the study of other worlds, such as the planets of the Solar System and even beyond. The study of systems larger than the earth itself usually forms part of Astronomy or Cosmology. The study of other planets is usually called planetary science. Alternative such as Areology (the study of Mars) have been proposed, but are not widely used.

Techniques As spatial interrelationships are key to this synoptic science, maps are a key tool. Classical cartography has been ed by a more modern approach to geographical analysis, computer-based geographic information systems (GIS). In their study, geographers use four interrelated approaches: • • • •

Systematic - Groups geographical knowledge into categories that can be explored globally. Regional - Examines systematic relationships between categories for a specific region or location on the planet. Descriptive - Simply specifies the locations of features and populations. Analytical - Asks why we find features and populations in a specific geographic area.

Cartography Cartography studies the representation of the Earth's surface with abstract symbols (map making). Although other subdisciplines of geography rely on maps for presenting their analyses, the actual making of maps is abstract enough to be regarded separately. Cartography has grown from a collection of drafting techniques into an actual science. Cartographers must learn cognitive psychology and ergonomics to understand which symbols convey information about the Earth most effectively, and behavioral psychology to induce the readers of their maps to act on the information. They must learn geodesy and fairly advanced mathematics to understand how the shape of the Earth affects the distortion of map symbols projected onto a flat surface for viewing. It can be said, without much controversy, that cartography is the seed from which the larger field of geography grew. Most geographers will cite a childhood fascination with maps as an early sign they would end up in the field.

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Geographic information systems Geographic information systems (GIS) deal with the storage of information about the Earth for automatic retrieval by a computer, in an accurate manner appropriate to the information's purpose. In addition to all of the other subdisciplines of geography, GIS specialists must understand computer science and database systems. GIS has revolutionized the field of cartography; nearly all mapmaking is now done with the assistance of some form of GIS software. GIS also refers to the science of using GIS software and GIS techniques to represent, analyze and predict spatial relationships. In this context, GIS stands for Geographic Information Science.

Remote sensing Remote sensing is the science of obtaining information about Earth features from measurements made at a distance. Remotely sensed data comes in many forms such as satellite imagery, aerial photography and data obtained from hand-held sensors. Geographers increasingly use remotely sensed data to obtain information about the Earth's land surface, ocean and atmosphere because it: a) supplies objective information at a variety of spatial scales (local to global), b) provides a synoptic view of the area of interest, c) allows access to distant and/or inaccessible sites, d) provides spectral information outside the visible portion of the electromagnetic spectrum, and e) facilitates studies of how features/areas change over time. Remotely sensed data may be analyzed either independently of, or in conjunction with, other digital data layers (e.g., in a Geographic Information System).

Quantitative methods Geostatistics deal with quantitative data analysis, specifically the application of statistical methodology to the exploration of geographic phenomena. Geostatistics is used extensively in a variety of fields including: hydrology, geology, petroleum exploration, weather analysis, urban planning, logistics, and epidemiology. The mathematical basis for geostatistics derives from cluster analysis, linear discriminant analysis and non-parametric statistical tests, and a variety of other subjects. Applications of geostatistics rely heavily on geographic information systems, particularly for the interpolation (estimate) of unmeasured points. Geographers are making notable contributions to the method of quantitative techniques.

Qualitative methods Geographic qualitative methods, or ethnographical; research techniques, are used by human geographers. In cultural geography there is a tradition of employing qualitative research techniques also used in anthropology and sociology. Participant observation and in-depth interviews provide human geographers with qualitative data.

History The oldest known world maps date back to ancient Babylon from the 9th century BC.[10] The best known Babylonian world map, however, is the Imago Mundi of 600 BC.[11] The map as reconstructed by Eckhard Unger shows Babylon on the Euphrates, surrounded by a circular landmass showing Assyria, Urartu[12] and several cities, in turn surrounded by a "bitter river" (Oceanus), with seven islands arranged around it so as to form a seven-pointed star. The accompanying text mentions seven outer regions beyond the encircling ocean. The descriptions of five of them have survived.[13] In contrast to the Imago Mundi, an earlier Babylonian world map dating back to the 9th century BC depicted Babylon as being further north from the center of the world, though it is not certain what that center was supposed to represent.[10] The ideas of Anaximander (c. 610 BC-c. 545 BC), considered by later Greek writers to be the true founder of geography, come to us through fragments quoted by his successors. Anaximander is credited with the invention of the gnomon,the simple yet efficient Greek instrument that allowed the early measurement of latitude. Thales, Anaximander is also credited with the prediction of eclipses. The foundations of geography can be traced to the

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Geography ancient cultures, such as the ancient, medieval, and early modern Chinese. The Greeks, who were the first to explore geography as both art and science, achieved this through Cartography, Philosophy, and Literature, or through Mathematics. There is some debate about who was the first person to assert that the Earth is spherical in shape, with the credit going either to Parmenides or Pythagoras. Anaxagoras was able to demonstrate that the profile of the Earth was circular by explaining eclipses. However, he still believed that the Earth was a flat disk, as did many of his contemporaries. One of the first estimates of the radius of the Earth was made by Eratosthenes.[14] The first rigorous system of latitude and longitude lines is credited to Hipparchus. He employed a sexagesimal system that was derived from Babylonian mathematics. The parallels and meridians were sub-divided into 360°, with each degree further subdivided 60′ (minutes). To measure the longitude at different location on Earth, he suggested using eclipses to determine the relative difference in time.[15] The extensive mapping by the Romans as they explored new lands would later provide a high level of information for Ptolemy to construct detailed atlases. He extended the work of Hipparchus, using a grid system on his maps and adopting a length of 56.5 miles for a degree.[16] From the 3rd century onwards, Chinese methods of geographical study and writing of geographical literature became much more complex than what was found in Europe at the time (until the 13th century).[17] Chinese geographers such as Liu An, Pei Xiu, Jia Dan, Shen Kuo, Fan Chengda, Zhou Daguan, and Xu Xiake wrote important treatises, yet by the 17th century, advanced ideas and methods of Western-style geography were adopted in China. During the Middle Ages, the fall of the Roman empire led to a shift in the evolution of geography from Europe to the Islamic world.[17] Muslim geographers such as Muhammad al-Idrisi produced detailed world maps (such as Tabula Rogeriana), while other geographers such as Yaqut al-Hamawi, Abu Rayhan Biruni, Ibn Battuta and Ibn Khaldun provided detailed s of their journeys and the geography of the regions they visited. Turkish geographer, Mahmud al-Kashgari drew a world map on a linguistic basis, and later so did Piri Reis (Piri Reis map). Further, Islamic scholars translated and interpreted the earlier works of the Romans and Greeks and established the House of Wisdom in Baghdad for this purpose.[18] Abū Zayd al-Balkhī, originally from Balkh, founded the "Balkhī school" of terrestrial mapping in Baghdad.[19] Suhrāb, a late tenth century Muslim geographer, accompanied a book of geographical coordinates with instructions for making a rectangular world map, with equirectangular projection or cylindrical equidistant projection.[19] In the early 11th century, Avicenna hypothesized on the geological causes of mountains in The Book of Healing (1027). Abu Rayhan Biruni (976-1048) first described a polar equi-azimuthal equidistant projection of the celestial sphere.[20] He was regarded as the most skilled when it came to mapping cities and measuring the distances between them, which he did for many cities in the Middle East and Indian subcontinent. He often combined astronomical readings and mathematical equations, in order to develop methods of pin-pointing locations by recording degrees of latitude and longitude. He also developed similar techniques when it came to measuring the heights of mountains, depths of valleys, and expanse of the horizon. He also discussed human geography and the planetary habitability of the Earth. He hypothesized that roughly a quarter of the Earth's surface is habitable by humans. He also calculated the latitude of Kath, Khwarezm, using the maximum altitude of the Sun, and solved a complex geodesic equation in order to accurately compute the Earth's circumference, which were close to modern values of the Earth's circumference.[21] His estimate of 6,339.9 km for the Earth radius was only 16.8 km less than the modern value of 6,356.7 km. In contrast to his predecessors who measured the Earth's circumference by sighting the Sun simultaneously from two different locations, al-Biruni developed a new method of using trigonometric calculations based on the angle between a plain and mountain top which yielded more accurate measurements of the Earth's circumference and made it possible for it to be measured by a single person from a single location.[22] He also published a study of map projections, Cartography, which included a method for projecting a hemisphere on a plane.

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The European Age of Discovery during the 16th and 17th centuries, where many new lands were discovered and s by European explorers such as Christopher Columbus, Marco Polo and James Cook, revived a desire for both accurate geographic detail, and more solid theoretical foundations in Europe. The problem facing both explorers and geographers was finding the latitude and longitude of a geographic location. The problem of latitude was solved long ago but that of longitude remained; agreeing on what zero meridian should be was only part of the problem. It was left to John Harrison to solve it by inventing the chronometer H-4, in 1760, and later in 1884 for the International Meridian Conference to adopt by convention the Greenwich meridian as zero meridian.[23] The 18th and 19th centuries were the times when geography became recognized as a discrete academic discipline and became part of a typical university curriculum in Europe (especially Paris and Berlin). Self portrait of Alexander von Humboldt, one of The development of many geographic societies also occurred during the early pioneers of geography the 19th century with the foundations of the Société de Géographie in 1821,[24] the Royal Geographical Society in 1830,[25] Russian Geographical Society in 1845,[26] American Geographical Society in 1851,[27] and the National Geographic Society in 1888.[28] The influence of Immanuel Kant, Alexander von Humboldt, Carl Ritter and Paul Vidal de la Blache can be seen as a major turning point in geography from a philosophy to an academic subject. Over the past two centuries the advancements in technology such as computers, have led to the development of geomatics and new practices such as participant observation and geostatistics being incorporated into geography's portfolio of tools. In the West during the 20th century, the discipline of geography went through four major phases: environmental determinism, regional geography, the quantitative revolution, and critical geography. The strong interdisciplinary links between geography and the sciences of geology and botany, as well as economics, sociology and demographics have also grown greatly especially as a result of Earth System Science that seeks to understand the world in a holistic view.

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Notable geographers • Eratosthenes (276BC - 194BC) - calculated the size of the Earth. • Ptolemy (c.90–c.168) - compiled Greek and Roman knowledge into the book Geographia. • Al Idrisi (Arabic: ‫يسيردإلا دمحم هللا دبع وبأ‬‎; Latin: Dreses) (1100–1165/66) - author of Nuzhatul Mushtaq. • Gerardus Mercator (1512–1594) - innovative cartographer produced the mercator projection • Alexander von Humboldt (1769–1859) - Considered Father of modern geography, published the Kosmos and founder of the sub-field biogeography. • Carl Ritter (1779–1859) - Considered Father of modern geography. Occupied the first chair of geography at Berlin University. • Arnold Henry Guyot (1807–1884) - noted the structure of glaciers and advanced understanding in glacier motion, especially in fast ice flow.

The Geographer by Johannes Vermeer

• William Morris Davis (1850–1934) - father of American geography and developer of the cycle of erosion. • Paul Vidal de la Blache (1845–1918) - founder of the French school of geopolitics and wrote the principles of human geography. • • • • • • • • • •

Sir Halford John Mackinder (1861–1947) - Co-founder of the LSE, Geographical Association Carl O. Sauer (1889–1975) - Prominent cultural geographer Walter Christaller (1893–1969) - human geographer and inventor of Central place theory. Yi-Fu Tuan (1930-) - Chinese-American scholar credited with starting Humanistic Geography as a discipline. David Harvey (1935-) - Marxist geographer and author of theories on spatial and urban geography, winner of the Vautrin Lud Prize. Edward Soja (born 1941) - Noted for his work on regional development, planning and governance along with coining the Synekism and Postmetropolis. Michael Frank Goodchild (1944-) - prominent GIS scholar and winner of the RGS founder's medal in 2003. Doreen Massey (1944-) - Key scholar in the space and places of globalization and its pluralities, winner of the Vautrin Lud Prize. Nigel Thrift (1949-) - originator of non-representational theory. Ellen Churchill Semple (1863–1932) - She was America's first influential female geographer.

Institutions and societies • • • • • •

Anton Melik Geographical Institute (Slovenia) National Geographic Society (U.S.) American Geographical Society (U.S.) National Geographic Bee (U.S.) Royal Canadian Geographical Society (Canada) Royal Geographical Society (UK)

Geography

Publications • African Geographical Review • Geographical Review

Notes and references [1] "Online Etymology Dictionary" (http:/ / www. etymonline. com/ index. php?term=geography). Etymonline.com. . Retrieved 2009-04-17. [2] "Geography" (http:/ / dictionary. reference. com/ browse/ geography). The American Heritage Dictionary/ of the English Language, Fourth Edition. Houghton Mifflin Company. . Retrieved October 9, 2006. [3] Pattison, W.D. (1990). "The Four Traditions of Geography" (http:/ / www. geog. ucsb. edu/ ~kclarke/ G200B/ four_20traditions_20of_20geography. pdf). Journal of Geography 89 (5): 202–6. doi:10.1080/00221349008979196. ISSN 0022-1341. . Reprint of a 1964 article. [4] Bonnett, Alastair What is Geography? London, Sage, 2008 [5] http:/ / web. clas. ufl. edu/ s/ morgans/ lecture_2. prn. pdf [6] "1(b). Elements of Geography" (http:/ / www. physicalgeography. net/ fundamentals/ 1b. html). Physicalgeography.net. . Retrieved 2009-04-17. [7] Hayes-Bohanan, James. "What is Environmental Geography, Anyway?" (http:/ / webhost. bridgew. edu/ jhayesboh/ environmentalgeography. htm). . Retrieved October 9, 2006. [8] Hughes, William. (1863). The Study of Geography. Lecture delivered at King's College, London by Sir Marc Alexander. Quoted in Baker, J.N.L (1963). The History of Geography. Oxford: Basil Blackwell. pp. 66. ISBN 0853280223. [9] "What is geography?" (http:/ / web. archive. org/ web/ 20061006152742/ http:/ / www. aag. org/ Careers/ What_is_geog. html). AAG Career Guide: Jobs in Geography and related Geographical Sciences. Association of American Geographers. Archived from the original (http:/ / www. aag. org/ Careers/ What_is_geog. html) on October 6, 2006. . Retrieved October 9, 2006. [10] Kurt A. Raaflaub & Richard J. A. Talbert (2009). Geography and Ethnography: Perceptions of the World in Pre-Modern Societies. John Wiley & Sons. p. 147. ISBN 1405191465 [11] Siebold, Jim Slide 103 (http:/ / www. henry-davis. com/ MAPS/ Ancient Web Pages/ 103. html) via henry-davis.com - accessed 2008-02-04 [12] http:/ / www. jstor. org/ pss/ 1151277 IMAGO MVNDI, Vol.48 pp.209 [13] Finel, Irving (1995). A to the map of the world: A notable discover. pp. 26–27. [14] Jean-Louis and Monique Tassoul (1920). A Concise History of Solar and Stellar Physics. London: Princeton University Press. ISBN 069111711X. [15] "Hipparcos of Rhodes" (http:/ / astrogeology. usgs. gov/ HotTopics/ index. php?/ archives/ 147-Names-for-the-Columbia-astronauts-provisionally-approved. html). Technology Museum of Thessaloniki. 2001. . Retrieved 2006-10-16. [16] Sullivan, Dan (2000). "Mapmaking and its History" (http:/ / www. math. rutgers. edu/ ~cherlin/ History/ Papers2000/ sullivan. html). Rutgers University. . Retrieved 2006-10-16. [17] Needham, Joseph (1986). Science and Civilization in China: Volume 3. Taipei: Caves Books, Ltd. Page 512. [18] "Education" (http:/ / www. islamicity. com/ education/ ihame/ default. asp?Destination=/ education/ ihame/ 20. asp). IslamiCity.com. . Retrieved 2009-04-17. [19] E. Edson and Emilie Savage-Smith, Medieval Views of the Cosmos, pp. 61-3, Bodleian Library, University of Oxford [20] David A. King (1996), "Astronomy and Islamic society: Qibla, gnomics and timekeeping", in Roshdi Rashed, ed., Encyclopedia of the History of Arabic Science, Vol. 1, p. 128-184 [153]. Routledge, London and New York. [21] James S. Aber (2003). Alberuni calculated the Earth's circumference at a small town of Pind Dadan Khan, District Jhelum, Punjab, Pakistan. Abu Rayhan al-Biruni (http:/ / academic. emporia. edu/ aberjame/ histgeol/ biruni/ biruni. htm), Emporia State University. [22] Lenn Evan Goodman (1992), Avicenna, p. 31, Routledge, ISBN 041501929X. [23] Aughton, Peter (2007). Voyages that changed the world (http:/ / books. google. com/ ?id=bz4GyOioMF4C& pg=RA1-PA164& dq=Voyages+ that+ changed+ the+ world+ H-4& cd=1#v=onepage& q=). Quercus. p. 164. ISBN 1847240040. . [24] "Société de Géographie, Paris, " (http:/ / www. socgeo. org/ index. html) (in French). . Retrieved 2007-01-15. [25] "" (http:/ / www. rgs. org/ AboutUs/ about+ us. htm). Royal Geographical Society. . Retrieved 2007-01-15. [26] "Русское Географическое Общество (основано в 1845 г.)" (http:/ / www. rgo. org. ru/ ). Rgo.org.ru. . Retrieved 2009-04-17. [27] "The American Geographical Society" (http:/ / www. amergeog. org/ ). Amergeog.org. 2009-04-02. . Retrieved 2009-04-17. [28] "Inspiring People to Care About the Planet" (http:/ / www. nationalgeographic. com/ index. html). National Geographic. 2002-10-17. . Retrieved 2009-04-17.

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Limnology

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Limnology Limnology (pronounced /lɪmˈnɒlədʒi/ lim-NOL-ə-jee; from Greek: Λίμνη limnee, "lake"; and λόγος, logos, "knowledge") is the study of inland waters. It is often regarded as a division of ecology or environmental science. It covers the biological, chemical, physical, geological, and other attributes of all inland waters (running and standing waters, both fresh and saline, natural or man-made). This includes the study of lakes and ponds, rivers, springs, streams and wetlands.[1] A more recent sub-discipline of limnology, termed landscape limnology, studies, manages, and conserves these aquatic ecosystems using a landscape perspective.

Lake Hawea, New Zealand

Limnology is closely related to aquatic ecology and hydrobiology, which study aquatic organisms in particular regard to their hydrological environment.

History The term limnology was coined by François-Alphonse Forel (1841–1912) who established the field with his studies of Lake Geneva. Interest in the discipline rapidly expanded, and in 1922 August Thienemann (a German zoologist) and Einar Naumann (a Swedish botanist) co-founded the International Society of Limnology (SIL, for originally Societas Internationalis Limnologiae). Forel's original definition of limnology, "the oceanography of lakes", was expanded to encom the study of all inland waters.[1] Prominent early American limnologists included G. Evelyn Hutchinson, Ed Deevey, E. A. Birge, and C. Juday.[2]

Lake Limnology Limnology classifies lakes according to the trophic state index. [1] An oligotrophic lake is characterised by relatively low levels of primary production and low levels of nutrients. An eutrophic lake has high levels of primary productivity due to very high nutrient levels. Eutrophication of a lake can lead to algal blooms. Dystrophic lakes have high levels of humic matter and typically has yellow-brown tea coloured waters. [1] This classification system is not very clear cut and can be seen as more of a spectrum encoming the various levels of productivity.

Limnology

Organizations • • • • • • • • • • • • •

American Society of Limnology and Oceanography Australian Society for Limnology European Society of Limnology and Oceanography Society of Limnology [3] Italian Association for Oceanology and Limnology (AIOL) [4] The Japanese Society of Limnology International Society of Limnology Brazilian Society of Limnology [5] New Zealand freshwater Sciences society [6] Southern African Society of Aquatic Scientists [7] Balaton Limnological Research Institute [8] Polish Limnological Society North American Benthological Society [9]

Journals • • • • • • • • • • • • • • • • •

Advances in Limnology Aquatic Conservation [10] Aquatic Ecology [11] Canadian Journal of Fisheries and Aquatic Sciences [12] Chinese Journal of Oceanology and Limnology Freshwater Biology [13] Hydrobiologia [14] Journal of Ecology and Fisheries Journal of Limnology [15] Limnologica Limnological Review [16] Journal of the North American Benthological Society [17] Limnology and Oceanography [18] Marine and Freshwater Research [19] New Zealand Journal of Marine and Freshwater Research [20] Review of Hydrobiology [21] River Research and Applications [22]

See also • • • • • • • •

Limnology publications G. Evelyn Hutchinson Freshwater biology Hydrology Lake aeration Lake ecosystem Landscape limnology Lentic ecosystems

• Limnic eruption • Lotic ecosystems • Marine biology

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Limnology • Oceanography • Paleolimnology

Notes [1] Wetzel, R.G. 2001. Limnology: Lake and River Ecosystems, 3rd ed. Academic Press (ISBN 0-12-744760-1) [2] Frey, D.G. (ed.), 1963. Limnology in North America. University of Wisconsin Press, Madison [3] http:/ / www. dgl-ev. de [4] http:/ / www. aiol. info [5] http:/ / www. sblimno. org. br/ [6] http:/ / freshwater. rsnz. org/ [7] http:/ / www. dwaf. gov. za/ iwqs/ sasaqs/ index. htm [8] http:/ / www. blki. hu/ BLRI/ index. htm [9] http:/ / www. benthos. org [10] http:/ / www. interscience. wiley. com/ journal/ aqc [11] http:/ / www. springer. com/ life+ sciences/ ecology/ journal/ 10452 [12] http:/ / pubs. nrc-cnrc. gc. ca/ rp-ps/ journalDetail. jsp?jcode=cjfas [13] http:/ / www. blackwellpublishing. com/ fwb [14] http:/ / www. springerlink. com/ content/ 100271/ [15] http:/ / www. iii. to. cnr. it/ pubblicaz/ jour_lim. htm [16] http:/ / ptlim. pl/ wydawnictwa. html [17] [18] [19] [20] [21] [22]

http:/ / www. benthos. org/ Journal-(JNABS). aspx http:/ / www. aslo. org/ http:/ / www. publish. csiro. au/ nid/ 126. htm http:/ / www. informaworld. com/ smpp/ title~content=t918959567~db=all http:/ / www. reviewofhydrobiology. com/ http:/ / www. interscience. wiley. com/ journal/ rra

References • • • • • • • •

Gerald A. Cole, Textbook of Limnology, 4th ed. (Waveland Press, 1994) ISBN 0-88133-800-1 Stanley Dodson, Introduction to Limnology (2005), ISBN 0-07-287935-1 A.J.Horne and C.R. Goldman: Limnology (1994), ISBN 0-07-023673-9 G. E. Hutchinson, A Treatise on Limnology, 3 vols. (1957–1975) - classic but dated H.B.N. Hynes, The Ecology of Running Waters (1970) Jacob Kalff, Limnology (Prentice Hall, 2001) B. Moss, Ecology of Fresh Waters (Blackwell, 1998) Robert G. Wetzel and Gene E. Likens, Limnological Analyses, 3rd ed. (Springer-Verlag, 2000)

External links • The History of Limnology at the University of Wisconsin–Madison (http://digital.library.wisc.edu/1711.dl/ UW.LimnHist): A digital resource documenting three generations of limnological research in Wisconsin. Much of the collection comes from the archives of the UW–Madison Center for Limnology. It focuses on three important pioneers of limnology, Dr. Edward A. Birge, Chancey Juday and Arthur D. Hasler, as well as Wisconsin research laboratories and field equipment. Presented by the University of Wisconsin Digital Collections Center. • Breaking new waters: a Century of Limnology at the University of Wisconsin (http://digital.library.wisc.edu/ 1711.dl/WI.WTBreakWaters): A special publication of the Wisconsin Academy of Sciences, Arts and Letters in celebration of a century of limnological research. • Limnological Institute of the Siberian Branch of the Russian Academy of Sciences (http://www.lin.irk.ru/eng/ about.htm)

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Glaciology

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Glaciology Glaciology (from Middle French dialect (Franco-Provençal): glace, "ice"; or Latin: glacies, "frost, ice"; and Greek: λόγος, logos, "speech" lit. "study of ice") is the study of glaciers, or more generally ice and natural phenomena that involve ice. Glaciology is an interdisciplinary earth science that integrates geophysics, geology, physical geography, geomorphology, climatology, meteorology, hydrology, biology, and ecology. The impact of glaciers on people includes the fields of human geography and anthropology. The discoveries of water ice on the Moon, Mars and Europa adds an extraterrestrial component to the field, as in "astroglaciology".

Lateral moraine on a glacier ing the Gorner Glacier, Zermatt, Switzerland. The moraine is the high bank of debris in the top left hand quarter of the picture. For more explanation, click on the picture.

Overview Areas of study within glaciology include glacial history and the reconstruction of past glaciation. A glaciologist is a person who studies glaciers. Glaciology is one of the key areas of polar research. A glacier is an extended mass of ice formed from snow falling and accumulating over the years and moving very slowly, either descending from high mountains, as in valley glaciers, or moving outward from centers of accumulation, as in continental glaciers.

Types There are two general categories of glaciation which glaciologists distinguish: alpine glaciation, accumulations or "rivers of ice" confined to valleys; and continental glaciation, unrestricted accumulations which once covered much of the northern continents. • Alpine - ice flows down the valleys of mountainous areas and forms a tongue of ice moving towards the plains below. Alpine glaciers tend to make the topography more rugged, by adding and improving the scale of existing features such as large ravines called cirques and ridges where the rims of two cirques meet called arêtes. • Continental - an ice sheet found today, only in high latitudes (Greenland/Antarctica), thousands of square kilometers in area and thousands of meters thick. These tend to smooth out the landscapes.

Glacially-carved Yosemite Valley, as seen from a plane

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Zones of glaciers • Accumulation, where the formation of ice is faster than its removal. • Wastage or Ablation, where the sum of melting and evaporation (sublimation) is greater than the amount of snow added each year.

Movement Ablation wastage of the glacier through sublimation, ice melting and iceberg calving. Ablation zone Area of a glacier in which the annual loss of ice through ablation exceeds the annual gain from precipitation. Arête an acute ridge of rock where two cirques abut. Bergshrund crevasse formed near the head of a glacier, where the mass of ice has rotated, sheared and torn itself apart in the manner of a geological fault. Cirque, corrie or cwm bowl shaped depression excavated by the source of a glacier. Creep adjustment to stress at a molecular level. Flow movement (of ice) in a constant direction. Fracture brittle failure (breaking of ice) under the stress raised when movement is too rapid to be accommodated by creep. It happens for example, as the central part of a glacier moves faster than the edges. Horn spire of rock formed by the headward erosion of a ring of cirques around a single mountain. It is an extreme case of an arête. Plucking/Quarrying where the adhesion of the ice to the rock is stronger than the cohesion of the rock, part of the rock leaves with the flowing ice. Tarn a lake formed in the bottom of a cirque when its glacier has melted. Tunnel valley The tunnel is that formed by hydraulic erosion of ice and rock below an ice sheet margin. The tunnel valley is what remains of it in the underlying rock when the ice sheet has melted.

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Glacial deposits Stratified Outwash sand/gravel from front of glaciers, found on a plain Kettles block of stagnant ice leaves a depression or pit Eskers steep sided ridges of gravel/sand, possibly caused by streams running under stagnant ice Kames stratified drift builds up low steep hills Varves alternating thin sedimentary beds (coarse and fine) of a proglacial lake. Summer conditions deposit more and coarser material and those of the winter, less and finer.

Unstratified Till-unsorted (glacial flour to boulders) deposited by receding/advancing glaciers, forming moraines, and drumlins Moraines (Terminal) material deposited at the end; (Ground) material deposited as glacier melts; (lateral) material deposited along the sides. Drumlins smooth elongated hills composed of till. Ribbed moraines large subglacial elongated hills transverse to former ice flow.

References • Benn, Douglas I. and David J. A. Evans. Glaciers and Glaciation. London; Arnold, 1998. ISBN 0-340-58431-9 • Greve, Ralf and Heinz Blatter. Dynamics of Ice Sheets and Glaciers. Berlin etc.; Springer, 2009. ISBN 978-3-642-03414-5 • Hambrey, Michael and Jürg Alean. Glaciers. 2nd ed. Cambridge and New York; Cambridge University Press, 2004. ISBN 0-521-82808-2 • Hooke, Roger LeB. Principles of Glacier Mechanics. 2nd ed. Cambridge and New York; Cambridge University Press, 2005. ISBN 0-521-54416-5 • Knight, Peter G. Glaciers. Cheltenham; Nelson Thornes, 1999. ISBN 0-7487-4000-7 • Paterson, W. Stanley B. The Physics of Glaciers. 3rd ed. Oxford etc.; Pergamon Press, 1994. ISBN 0-08-037944-3 • van der Veen, Cornelis J. Fundamentals of Glacier Dynamics. Rotterdam; A. A. Balkema, 1999. ISBN 90-5410-471-6

Glaciology

External links • • • • • • • • • • • • • • • •

International Glaciological Society (IGS) [1] International Association of Cryospheric Sciences (IACS) [2] Snow, Ice, and Permafrost Group, University of Alaska Fairbanks [3] Arctic and Alpine Research Group, University of Alberta [4] Glaciers online [5] World Data Centre for Glaciology, Cambridge, UK [6] National Snow and Ice Data Center, Boulder, Colorado [7] Global Land Ice Measurements from Space, USGS [8] North Cascade Glacier Climate Project [9] Centre for Glaciology, University of Wales [10] Caltech Glaciology Group [11] Glaciology Group, University of Copenhagen [12] Institute of Low Temperature Science, Sapporo [13] National Institute of Polar Research, Tokyo [14] Glaciology Group, University of Washington [15] Glaciology Laboratory, Universidad de Chile-Centro de Estudios Científicos, Valdivia [16]

• Russian Geographical Society (Moscow Centre) [17] - Glaciology Commission [18] • Institute of Meteorology and Geophysics, Univ. of Innsbruck, Austria. [19]

References [1] http:/ / www. igsoc. org/ [2] http:/ / www. cryosphericsciences. org/ [3] http:/ / www. gi. alaska. edu/ snowice/ [4] http:/ / arctic. eas. ualberta. ca/ [5] http:/ / www. glaciers-online. net/ [6] http:/ / wdcgc. spri. cam. ac. uk/ [7] http:/ / www. nsidc. org/ [8] http:/ / www. glims. org/ [9] http:/ / www. nichols. edu/ departments/ glacier/ [10] http:/ / www. aber. ac. uk/ ~glawww/ [11] http:/ / glaciology. caltech. edu/ [12] http:/ / www. glaciology. gfy. ku. dk/ [13] http:/ / www. lowtem. hokudai. ac. jp/ english/ [14] http:/ / www. nipr. ac. jp/ [15] http:/ / www. geophys. washington. edu/ Surface/ Glaciology/ [16] http:/ / www. glaciologia. cl [17] http:/ / rgo. msk. ru/ [18] http:/ / rgo. msk. ru/ commissions/ glaciology/ [19] http:/ / imgi. uibk. ac. at/ iceclim/ intro

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Atmospheric sciences

Atmospheric sciences Atmospheric sciences is an umbrella term for the study of the atmosphere, its processes, the effects other systems have on the atmosphere, and the effects of the atmosphere on these other systems. Meteorology includes atmospheric chemistry and atmospheric physics with a major focus on weather forecasting. Climatology is the study of atmospheric changes (both long and short-term) that define average climates and their change over time, due to both natural and anthropogenic climate variability. Aeronomy is the study of the upper layers of the atmosphere, where dissociation and ionization are important. Atmospheric science has been extended to the field of planetary science and the study of the atmospheres of the planets of the solar system. Experimental instruments used in atmospheric sciences include satellites, rocketsondes, radiosondes, weather balloons, and lasers. The term aerology (from Greek ἀήρ, aēr, "air"; and -λογία, -logia) is sometimes used as an alternative term for the study of Earth's atmosphere.

Atmospheric chemistry Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary field of research and draws on environmental chemistry, physics, meteorology, computer modeling, oceanography, geology and volcanology and other disciplines. Research is increasingly connected with other areas of study such as climatology. The composition and chemistry of the atmosphere is of importance for several reasons, but primarily because of the interactions between the atmosphere and living organisms. The composition of the Earth's atmosphere has been changed by human activity and some of these changes are harmful to human health, crops and ecosystems. Examples of problems which have been addressed by atmospheric chemistry include acid rain, photochemical smog and global warming. Atmospheric chemistry seeks to understand the causes of these problems, and by obtaining a theoretical understanding of them, allow possible solutions to be tested and the effects of changes in government policy evaluated.

Atmospheric dynamics Atmospheric dynamics involves the study of observations and theory dealing with all motion systems of meteorological importance. The list includes diverse phenomena as thunderstorms, tornadoes, gravity waves, tropical cyclones, extratropical cyclones, jet streams, and global-scale circulations. The goal of dynamical studies is to explain the observed circulations on the basis of fundamental principles from physics. The objectives of such studies include improving weather forecasting, developing methods for predicting seasonal and interannual climate fluctuations, and understanding the implications of human-induced perturbations (e.g., increased carbon dioxide concentrations or depletion of the ozone layer) on the global climate.[1]

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Atmospheric sciences

Atmospheric physics Atmospheric physics is the application of physics to the study of the atmosphere. Atmospheric physicists attempt to model Earth's atmosphere and the atmospheres of the other planets using fluid flow equations, chemical models, radiation balancing, and energy transfer processes in the atmosphere and underlying oceans. In order to model weather systems, atmospheric physicists employ elements of scattering theory, wave propagation models, cloud physics, statistical mechanics and spatial statistics which are highly mathematical and related to physics. It has close links to meteorology and climatology and also covers the design and construction of instruments for studying the atmosphere and the interpretation of the data they provide, including remote sensing instruments. In the UK, atmospheric studies are underpinned by the Meteorological Office. Divisions of the U.S. National Oceanic and Atmospheric istration (NOAA) oversee research projects and weather modeling involving atmospheric physics. The U.S. National Astronomy and Ionosphere Center also carries out studies of the high atmosphere.

Climatology In contrast to meteorology, which studies short term weather systems lasting up to a few weeks, climatology studies the frequency and trends of those systems. It studies the periodicity of weather events over years to millennia, as well as changes in long-term average weather patterns, in relation to atmospheric conditions. Climatologists, those who practice climatology, study both the nature of climates - local, regional or global and the natural or human-induced factors that cause climates to change. Climatology considers the past and can help predict future climate change. Phenomena of climatological interest include the atmospheric boundary layer, circulation patterns, heat transfer (radiative, convective and latent), interactions between the atmosphere and the oceans and land surface (particularly vegetation, land use and topography), and the chemical and physical Regional impacts of warm ENSO episodes (El Niño). composition of the atmosphere. Related disciplines include astrophysics, atmospheric physics, chemistry, ecology, geology, geophysics, glaciology, hydrology, oceanography, and volcanology.

Atmospheres on other planets

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Atmospheric sciences

All of the Solar System planets have atmospheres as their large masses mean gravity is strong enough to keep gaseous particles close to the surface. The larger gas giants are massive enough to keep large amounts of the light gases hydrogen and helium close by, while the smaller planets lose these gases into space.[2] The composition of the Earth's atmosphere is different from the other planets because the various life processes that have transpired on the planet have introduced free molecular oxygen.[3] The only solar planet Earth's atmosphere without a true atmosphere is Mercury which had it mostly, although not entirely, blasted away by the solar wind.[4] The only moon that has retained a dense atmosphere is Titan. There is a thin atmosphere on Triton, and a trace of an atmosphere on the Moon. Planetary atmospheres are affected by the varying degrees of energy received from either the Sun or their interiors, leading to the formation of dynamic weather systems such as hurricanes, (on Earth), planet-wide dust storms (on Mars), an Earth-sized anticyclone on Jupiter (called the Great Red Spot), and holes in the atmosphere (on Neptune).[5] At least one extrasolar planet, HD 189733 b, has been claimed to possess such a weather system, similar to the Great Red Spot but twice as large.[6] Hot Jupiters have been shown to be losing their atmospheres into space due to stellar radiation, much like the tails of comets.[7] [8] These planets may have vast differences in temperature between their day and night sides which produce supersonic winds,[9] although the day and night sides of HD 189733b appear to have very similar temperatures, indicating that planet's atmosphere effectively redistributes the star's energy around the planet.[6]

References [1] University of Washington. Atmospheric Dynamics. (http:/ / www. atmos. washington. edu/ academic/ atmosdyn. html) Retrieved on 1 June 2007. [2] Sheppard, Scott S.; Jewitt, David; Kleyna, Jan (2005). "An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness". The Astronomical Journal 129: 518–525. doi:10.1086/426329. arXiv:astro-ph/0410059v1. [3] Zeilik, Michael A.; Gregory, Stephan A. (1998). Introductory Astronomy & Astrophysics (4th ed.). Saunders College Publishing. pp. 67. ISBN 0030062284. [4] Hunten D. M., Shemansky D. E., Morgan T. H. (1988), The Mercury atmosphere, In: Mercury (A89-43751 19-91). University of Arizona Press, pp. 562–612 [5] Harvey, Samantha (1 May 2006). "Weather, Weather, Everywhere?" (http:/ / solarsystem. nasa. gov/ scitech/ display. cfm?ST_ID=725). NASA. . Retrieved 9 September 2007. [6] Knutson, Heather A.; Charbonneau, David; Allen, Lori E.; Fortney, Jonathan J. (2007). "A map of the day-night contrast of the extrasolar planet HD 189733b". Nature 447 (7141): 183. doi:10.1038/nature05782. PMID 17495920. (Related press release (http:/ / www. cfa. harvard. edu/ press/ 2007/ pr200713. html)) [7] Weaver, D.; Villard, R. (31 January 2007). "Hubble Probes Layer-cake Structure of Alien World's Atmosphere" (http:/ / hubblesite. org/ newscenter/ archive/ releases/ 2007/ 07/ full/ ). University of Arizona, Lunar and Planetary Laboratory (Press Release). . Retrieved 15 August 2007. [8] Ballester, Gilda E.; Sing, David K.; Herbert, Floyd (2007). "The signature of hot hydrogen in the atmosphere of the extrasolar planet HD 209458b". Nature 445 (7127): 511. doi:10.1038/nature05525. PMID 17268463. [9] Harrington, Jason; Hansen, Brad M.; Luszcz, Statia H.; Seager, Sara (2006). "The phase-dependent infrared brightness of the extrasolar planet Andromeda b". Science 314 (5799): 623. doi:10.1126/science.1133904. PMID 17038587. (Related press release (http:/ / www. nasa. gov/ vision/ universe/ starsgalaxies/ spitzer-20061012. html))

External links • Atmospheric fluid dynamics applied to weather maps (http://www.stuffintheair.com/chasing-storms.html) Principles such as Advection, Deformation and Vorticity

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Article Sources and Contributors

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Article Sources and Contributors Jonmarbury, Joseaperez, Joshdboz, JoshuaZ, Jossi, Jusdafax, KGasso, Khukri, Kpjas, Krclathrate, Kuru, KyraVixen, L Kensington, Leighmo, Leonini, Leuko, Levineps, Light current, Lir, Logiphile, Loren.wilton, MBisanz, MER-C, MPF, MPerel, Mac Davis, Marshman, Materialscientist, Mav, Maxis ftw, Mdd, Mdebets, Michael riber jorgensen, Mintleaf, Mutiny, Mwilso24, Mysdaao, Nakon, Naruto404, NawlinWiki, Neo139, Netalarm, Noirdez, Noone, NuclearWarfare, Omicronpersei8, Onco p53, Ottershrew, Paleorthid, Palica, Panyd, Pdcook, Pengo, Peter Karlsen, Pgk, Phasechange, Philip Trueman, Piano non troppo, Picapica, PigFlu Oink, Pinky sl, Plumbago, Profg, Pádraic MacUidhir, Q Science, Quintote, R0pe-196, REL1870, RJBurkhart, RJBurkhart3, RJHall, Rachel Pearce, RadioFan, Reach Out to the Truth, Recognizance, Redfarmer, Renata, RexNL, Rgoodermote, Rholton, Rhrad, Rich Farmbrough, Richss, Rjwilmsi, Rob Hooft, Rokfaith, Ronhjones, Rpatel10, Ryan Postlethwaite, Ryanjunk, Sadi 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JeremyA, Jerry 250, JesseGarrett, JesseW, Jfire, Jgnwb, Jguk, Jguk 2, Jh99, Jimbreed, Jmw0000, Jni, Jobbie12345, Joelr31, JonHarder, Jonny-mt, Jose77, Joseph Solis in Australia, Joymmart, Jwy, KC0ZHQ, KPH2293, Kablammo, Kappa, Karl Dickman, Kate, Keelm, Kibblethefast, Kiran the great, KittenKrazy, Kkmurray, Kmweber, Koavf, Komencanto, Kornfan71, Kpjas, KrisK, Kukuman, Kuru, La Parka Your Car, Lakshmikanthkumar, Laleena, Lancevortex, Landon1980, Latasupriya, Latitude0116, Laurel Bush, Leszek Jańczuk, Lexor, Liamsmyth, Lightmouse, Lights, Lingpingming, Llull, Locos epraix, Lordsatri, Luftikus143, Luxborealis, MER-C, MONGO, MaNeMeBasat, Maelnuneb, Maestrosync, Magister Mathematicae, Maharashtraexpress, Majorly, Malhonen, Malo, Man vyi, Mangojuice, Mani1, Mannafredo, Mappychris, Marvolo Gaunt, MarylandArtLover, Masterpiece2000, Materialscientist, Mattrosenberg, Mauler90, Maurreen, Mav, Mayumashu, Mboverload, Mcastrence, Mclechalle, Mcleodc123, Mcoxhk, Meegs, Menchi, Mereien, Miaow Miaow, MicahDCochran, Michael Hardy, Michaelfavor, Michfan2123, Mihai, Mike Rosoft, Mike.lifeguard, Mkbnett, Modernist, Momo erez, Monishasarkar, Monkeychic94, Mooncheese, Mosesofmason, Moverton, Moyabrit, Mschel, Muchosucko, Muriel Gottrop, Mxn, My76Strat, Mysterious BIG, Nakon, Natcase, Navyseal300, NawlinWiki, Nayvik, Neelix, Netoholic, Neutrality, NevilleDNZ, NewEnglandYankee, Nichalp, NickBush24, NickVanLiefferinge, Nikai, Nikola Smolenski, Nivix, Noctibus, Node ue, Nordlending, Norm, Noticket, Nov ialiste, Nuke guy, Numbo3, Ocatecir, Oneagainstwill, Oore, Orangutan, Orbias, Otend, Ottawa4ever, Oupblog, Owainjones2, OwenX, Oxymoron83, PFHLai, PSUMark2006, Panwan, Patar knight, Patrick, Paul Ganssle, Peatbrazier, Perceval, Perdevise, Perfectblue97, PericlesofAthens, Peruvianllama, Peshandratmin, PeterSymonds, Phaedriel, Philip Trueman, Pietro, Pinethicket, Piotrus, Pleasantville, Plimfix, Polk09, Pollinator, Poor Yorick, Pornofreak, Prashanthns, PrestonH, Prolog, Python eggs, Quadell, Quintessent, RJHall, RaCha'ar, RadarCzar, RafaAzevedo, Random 39849958, RandomP, Rasmus Faber, Razorflame, Rdsmith4, Reedy, Rettetast, RexNL, Rhobite, Rholton, Riana, Rich Farmbrough, RichPrez6, RichardF, Rick.G, Rishi agrawal, Rkef, Roastytoast, Rob Hooft, Romanm, Rooster30792, Roryf1, Rustyfence, Rxnd, RyanParis, Ryulong, SEWilco, SJ07060, SJP, SMasters, Sadads, Saikiri, Saluyot, Sam Korn, SamEV, Samtheboy, Samuelsen, Sardanaphalus, SchfiftyThree, Sciurinæ, Scott14, Sdhfjdhjkhdsjkf, Sean Whitton, Searchme, Seb az86556, Secfan, Secretlondon, Sengkang, Seraphim, Shabnam.garg, Shamusmccutthroat, Shappy, Shimgray, Sibi antony, SimonP, Simrit, SincereGuy, Sjakkalle, Skarebo, Skizzik, Slakr, Sluzzelin, Smalljim, Smarkflea, Smfairlie, Smile2me123, Snarfsnarf, SpLoT, Spangineer, Spencer, Spundun, Stan46998, Steinsky, Stephen Gilbert, Stephenb, Steven Zhang, Stormie, StuffOfInterest, Sunderland06, Sunray, Superm401, Svick, Swatkatz14, Sword of Light, Syncategoremata, Taejin, Tapir Terrific, 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Article Sources and Contributors Thezebutsaremadeforwalking, Think outside the box, Thw1309, Tiddly Tom, Tide rolls, Timberframe, Timbouctou, Timir Saxa, Tloupe, Tmcw, Tobby72, Tobias Conradi, Toby Bartels, Tofutwitch11, Tom Peters, TomPhil, Tombomp, Tommy2010, Tomsheldon, Tpbradbury, Traroth, Treisijs, Trilinguist, Triona, Troylake, Trysha, TunaSunrise, Twerbrou, Twinsday, Tymyyyy, Tyrol5, Ubardak, Ukabia, Ultratomio, Unfree, Unyoyega, Ute in DC, Valkass, Vaughan Pratt, Vera Cruz, Versageek, Violetriga, Viriditas, Vivio Testarossa, Voyagerfan5761, Vrenator, Vsmith, Walkerma, Waybuta, Waypoints, WeißNix, Wereon, Wetman, WhisperToMe, Wikiman405, Wknight94, Wlievens, WojPob, Wotloni2, XJamRastafire, Yamamoto Ichiro, Yarnalgo, Yboord028, Yidisheryid, Zanimum, Zap Rowsdower, Zenlax, Ziggurat, Zondor, ZooPro, ♥HollisterHottie!♥, 1138 anonymous edits Limnology  Source: http://en.wikipedia.org/w/index.php?oldid=409891856  Contributors: APH, Achilles.g, Afil, Ahmedfreebird, Ahoerstemeier, Akendall, AlexD, Anyeverybody, Aphilo, Asvestomix, Aude, Ben.c.roberts, Bjankuloski06en, BlankVerse, Borgx, CKarnstein, Chavanrj, ChemGardener, Cless Alvein, Colinbi, CultureDrone, DMacks, Daarznieks, Daniel Collins, Drunken Pirate, Epipelagic, Fkornel, Fritz Haendel, Fvasconcellos, Gencerturkmen, George Rodney Maruri Game, Geozt, GregorB, Hdynes, Headbomb, Heron, John, Kevin Forsyth, Kosebamse, Kristaga, Kuru, Kwamikagami, Lesfreck, Macaco, Magnus Manske, Martarius, Maurreen, Mayumashu, Mircea cs, Mitrius, Njatel, Phantomsteve, Plumbago, Quadell, Quintote, Rich Farmbrough, Rrburke, Runningonbrains, S19991002, Salix alba, Spalding, Spencek12, Stan Shebs, Stefeyboy, Steveprutz, Thedugganaut, Thpe, ValM.B., Velella, Wetman, Wikigratia, Wombatko, Yk Yk Yk, Zfr, Александър, ‫יבצ לאינד‬, ‫ملاع بوبحم‬, 108 anonymous edits Glaciology  Source: http://en.wikipedia.org/w/index.php?oldid=409329767  Contributors: *drew, .:Ajvol:., Adambro, Alan Liefting, AlexD, Alexandra lb, Altenmann, Anna Frodesiak, Aude, Awickert, BS Thurner Hof, Betsythedevine, Brianjohn, CSWarren, Crampon, Cuppysfriend, D, DARTH SIDIOUS 2, Daniel Collins, Dentren, DerHexer, Discospinster, Docbase, Duffman, Figma, Gene Nygaard, Glane23, Glenn, Hadal, Hdynes, JForget, Joemacgregor, Ju lien, Kr-val, KuroiShiroi, Lolipop123, Lumos3, MONGO, Maadio, Maniac18, Mikenorton, NatureA16, Newyorxico, Niels G. Mortensen, Novangelis, Nurg, Omnipaedista, Paine Ellsworth, Paulbalegend, Pejman47, Peltoms, Plumbago, Polargeo, Prolog, Qfl247, Quentar, RJFJR, RJP, Ragger65, Rd232, RedWolf, Ringbang, Sbowers3, Siim, St.Geoluca Hadge, Stan Shebs, Stefeyboy, Tanakeame, That Guy, From That Show!, Themolecule, Vsmith, Wavelength, Wendell, WereSpielChequers, Wsiegmund, Yk Yk Yk, ZooFari, Јованвб, 86 anonymous edits Atmospheric sciences  Source: http://en.wikipedia.org/w/index.php?oldid=410314897  Contributors: 216Kleopatra, A Voulgarakis, Ahmedfreebird, Ahoerstemeier, Barneca, Charles Matthews, CurtisSwain, Daniel Collins, DavidH, Djr32, El C, Enric Naval, Epolk, Evolauxia, FrVladimir, Goser, Hard Raspy Sci, IndulgentReader, Itamblyn, JAn Dudík, Jason Patton, Karnesky, Lexor, Mbeychok, Michael Hardy, N p holmes, Nick683, Nicklott, Pflatau, RJHall, Rich Farmbrough, Rossar, Shadowjams, Shizhao, SimonP, Thegreatdr, Timothy Clemans, Vextron, Vsmith, Yk Yk Yk, Zach 08, Zinjixmaggir, 33 anonymous edits

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Image Sources, Licenses and Contributors

Image Sources, Licenses and Contributors Image:Volcano q.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Volcano_q.jpg  License: Public Domain  Contributors: Axxgreazz, HenkvD, Quadell, Rémih, Saperaud, 2 anonymous edits Image:Limu o Pele.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Limu_o_Pele.jpg  License: Public Domain  Contributors: Gryffindor, Interiot, Juiced lemon Image:Magnetosphere rendition.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Magnetosphere_rendition.jpg  License: Public Domain  Contributors: w:NASANASA File:Earth symbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Earth_symbol.svg  License: Public Domain  Contributors: :OsgoodeLawyer File:The Earth seen from Apollo 17.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:The_Earth_seen_from_Apollo_17.jpg  License: Public Domain  Contributors: NASA. Photo taken by either Harrison Schmitt or Ron Evans (of the Apollo 17 crew). File:Solar Life Cycle.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Solar_Life_Cycle.svg  License: Public Domain  Contributors: :Oliverbeatson File:Terrestrial planet size comparisons.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Terrestrial_planet_size_comparisons.jpg  License: Public Domain  Contributors: wikipedia Brian0918 File:Earth-crust-cutaway-english.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Earth-crust-cutaway-english.svg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: :Surachit File:Tectonic plates (empty).svg  Source: http://en.wikipedia.org/w/index.php?title=File:Tectonic_plates_(empty).svg  License: Public Domain  Contributors: Dbenbenn, Denys, KJG2007, Santosga, Sting, Ævar Arnfjörð Bjarmason File:AYool topography 15min.png  Source: http://en.wikipedia.org/w/index.php?title=File:AYool_topography_15min.png  License: Creative Commons Attribution 2.5  Contributors: Plumbago File:Earth elevation histogram 2.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Earth_elevation_histogram_2.svg  License: Public Domain  Contributors: Original er was Citynoise at en.wikipedia File:MODIS Map.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:MODIS_Map.jpg  License: Public Domain  Contributors: Marit Jentoft-Nilsen File:Full moon partially obscured by atmosphere.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Full_moon_partially_obscured_by_atmosphere.jpg  License: Public Domain  Contributors: NASA File:Structure of the magnetosphere mod.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Structure_of_the_magnetosphere_mod.svg  License: Public Domain  Contributors: :Dashpool File:AxialTiltObliquity.png  Source: http://en.wikipedia.org/w/index.php?title=File:AxialTiltObliquity.png  License: Creative Commons Attribution 3.0  Contributors: :Dna- File:236084main MilkyWay-full-annotated.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:236084main_MilkyWay-full-annotated.jpg  License: Public Domain  Contributors: NASA/JPL-Caltech/R. Hurt File:The Earth and the Moon photographed from Mars orbit.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:The_Earth_and_the_Moon_photographed_from_Mars_orbit.jpg  License: Public Domain  Contributors: NASA/JPL-Caltech/University of Arizona Image:Earth-Moon.PNG  Source: http://en.wikipedia.org/w/index.php?title=File:Earth-Moon.PNG  License: Public Domain  Contributors: Earth-image from NASA; arrangement by brews_ohare File:Earth Moon Scale.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Earth_Moon_Scale.jpg  License: GNU Free Documentation License  Contributors: :Acdx File:Continents vide couleurs.png  Source: http://en.wikipedia.org/w/index.php?title=File:Continents_vide_couleurs.png  License: Creative Commons Attribution-Sharealike 2.5  Contributors: Bvontob, Cogito ergo sumo, Editor at Large, Gerrit, Lycaon, Marlus Gancher, OlympiADdict, QuartierLatin1968, Timeshifter, 7 anonymous edits File:Earthlights dmsp.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Earthlights_dmsp.jpg  License: Public Domain  Contributors: Data courtesy Marc Imhoff of NASA GSFC and Christopher Elvidge of NOAA NGDC. Image by Craig Mayhew and Robert Simmon, NASA GSFC. File:AS8-13-2329.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:AS8-13-2329.jpg  License: Public Domain  Contributors: Frank Borman Image:Water cycle.png  Source: http://en.wikipedia.org/w/index.php?title=File:Water_cycle.png  License: unknown  Contributors: AdiJapan, Helt, Juliancolton, Lupo, MARKELLOS, Marcbel, Masao jp, Saperaud, Seb az86556, Slady, ‫לורק לארשי‬, 9 anonymous edits File:Seawifs global biosphere.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Seawifs_global_biosphere.jpg  License: unknown  Contributors: Luis Fernández García, Tano4595, TheDJ, Túrelio, Yikrazuul, 1 anonymous edits Image:PIA04866 modest.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:PIA04866_modest.jpg  License: Public Domain  Contributors: NASA/JPL/Space Science Institute Image:Top of Atmosphere.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Top_of_Atmosphere.jpg  License: Public Domain  Contributors: NASA Earth Observatory File:Plates tect2 en.svg 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en.wikipedia File:Crosstail.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Crosstail.jpg  License: unknown  Contributors: http://en.wikipedia.org/wiki/:DavidStern File:Plasmoid.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Plasmoid.jpg  License: Public Domain  Contributors: Original er was DavidStern at en.wikipedia File:WasatchFault.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:WasatchFault.JPG  License: Creative Commons Attribution-Sharealike 3.0  Contributors: :Qfl247 Image:Geological map Britain William Smith 1815.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Geological_map_Britain_William_Smith_1815.jpg  License: unknown  Contributors: William Smith (1769-1839) Image:Geologic Clock with events and periods.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Geologic_Clock_with_events_and_periods.svg  License: Public Domain  Contributors: :Hardwigg, :Woudloper Image:Cross-cutting relations.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Cross-cutting_relations.svg  License: unknown  Contributors: :Woudloper Image:SEUtahStrat.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:SEUtahStrat.JPG  License: GNU Free Documentation License  Contributors: :Qfl247 File:rock cycle.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Rock_cycle.gif  License: Creative Commons Attribution 3.0  Contributors: :Awickert File:Active Margin.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Active_Margin.svg  License: unknown  Contributors: Ciaurlec, Editor at Large, Jo Weber, MushiHoshiIshi, Ö, Виктор В, 1 anonymous edits Image:Farallon Plate.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Farallon_Plate.jpg  License: Public Domain  Contributors: NASA Image:Jordens inre-numbers.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Jordens_inre-numbers.svg  License: GNU Free Documentation License  Contributors: Original Vectorization: Image:Earthquake wave paths.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Earthquake_wave_paths.svg  License: unknown  Contributors: SEWilco File:Volcanosed.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Volcanosed.svg  License: Public Domain  Contributors: :Hardwigg File:Fault types.png  Source: http://en.wikipedia.org/w/index.php?title=File:Fault_types.png  License: unknown  Contributors: Jide, Kelson, Koba-chan, MushiHoshiIshi, W!B:, Yuval Madar, Zimbres, 4 anonymous edits File:Antecline (PSF).png  Source: http://en.wikipedia.org/w/index.php?title=File:Antecline_(PSF).png  License: unknown  Contributors: Bastique, Igno2, PatríciaR, W!B: File:Kittatinny Mountain Cross Section.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Kittatinny_Mountain_Cross_Section.jpg  License: Public Domain  Contributors: United States Geological Survey Image:Brunton.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Brunton.JPG  License: Creative Commons Attribution-Sharealike 3.0  Contributors: :Qfl247 File:USGS 1950s mapping field camp.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:USGS_1950s_mapping_field_camp.jpg  License: Public Domain  Contributors: US Geological Survey

121

Image Sources, Licenses and Contributors File:PDA Mapping.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:PDA_Mapping.jpg  License: Public Domain  Contributors: US Geological Survey: Nathan Wood Image:lecia dmrx.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Lecia_dmrx.jpg  License: unknown  Contributors: Original er was Mwtoews at en.wikipedia File:Orogenic wedge.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Orogenic_wedge.jpg  License: Public Domain  Contributors: Dwight C. Bradley, Robert D. Tucker, Daniel R. Lux, Anita G. Harris, and D. Colin McGregor File:Exploration geologist.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Exploration_geologist.jpg  License: Public Domain  Contributors: Geoz, Lysippos, Tetris L, 1 anonymous edits File:Mars Viking 21i093.png  Source: http://en.wikipedia.org/w/index.php?title=File:Mars_Viking_21i093.png  License: Public Domain  Contributors: "Roel van der Hoorn (Van der Hoorn)" Image:Mudlogging.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Mudlogging.JPG  License: Creative Commons Attribution-Sharealike 3.0  Contributors: :Qfl247 Image:GCRockfall.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:GCRockfall.JPG  License: Creative Commons Attribution-Sharealike 3.0  Contributors: :Qfl247 Image:Soil sci.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Soil_sci.jpg  License: Public Domain  Contributors: Duesentrieb, Paleorthid Image:Soil Survey-Sample.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Soil_Survey-Sample.jpg  License: Public Domain  Contributors: H2O, Monkeybait Image:Global soil regions.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Global_soil_regions.jpg  License: Public Domain  Contributors: United States Department of Agriculture File:Thermohaline Circulation 2.png  Source: http://en.wikipedia.org/w/index.php?title=File:Thermohaline_Circulation_2.png  License: Public Domain  Contributors: Robert Simmon, NASA. Minor modifications by w::Dragons flightRobert A. Rohde also released to the w:public domainpublic domain File:Gulf stream map.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Gulf_stream_map.gif  License: Public Domain  Contributors: Benjamin Franklin. Original er was Zeamays at en.wikipedia File:Ocean currents 1911.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Ocean_currents_1911.jpg  License: Public Domain  Contributors: David Kernow, F1jmm, Geagea, Infrogmation, Roke, SEWilco, Saperaud, W!B: Image:Antarctic frontal-system hg.png  Source: http://en.wikipedia.org/w/index.php?title=File:Antarctic_frontal-system_hg.png  License: Attribution  Contributors: :Hgrobe File:World-map-2004-cia-factbook-large-1.7m-whitespace-removed.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:World-map-2004-cia-factbook-large-1.7m-whitespace-removed.jpg  License: Public Domain  Contributors: Badseed, Beltz, Herald Alberich, Mach, 9 anonymous edits File:Línea de Wallace.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Línea_de_Wallace.jpg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: Alberto Salguero, 2 anonymous edits File:Cyclone Catarina from the ISS on March 26 2004.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Cyclone_Catarina_from_the_ISS_on_March_26_2004.JPG  License: Public Domain  Contributors: Astronaut photograph ISS008-E-19646 was taken March 7, 2004, with a Kodak DCS760 digital camera equipped with an 50-mm lens, and is provided by the Earth Observations Laboratory, Johnson Space Center. File:90 mile beach.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:90_mile_beach.jpg  License: unknown  Contributors: 2000, ComputerHotline, Fir0002, Pierre cb, Saperaud, Shiftchange, Thuresson File:Gavin Plant.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Gavin_Plant.JPG  License: Creative Commons Attribution 2.5  Contributors: Original er was Analogue Kid at en.wikipedia File:Meridian convergence and spehrical excess.png  Source: http://en.wikipedia.org/w/index.php?title=File:Meridian_convergence_and_spehrical_excess.png  License: GNU Free Documentation License  Contributors: :E^(nix) File:Delicate Arch LaSalle.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Delicate_Arch_LaSalle.jpg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: Original er was Mlcreech at en.wikipedia File:Receding glacier-en.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Receding_glacier-en.svg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: :Lycaon File:Meander.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Meander.svg  License: Public Domain  Contributors: USDA & w::MysidMysid File:Khajuraho-landscape.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Khajuraho-landscape.jpg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: Original er was Willow4 at en.wikipedia File:World11.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:World11.jpg  License: unknown  Contributors: Original er was Vsmith at en.wikipedia File:Soil profile.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Soil_profile.jpg  License: Public Domain  Contributors: Duesentrieb, Juan de Vojníkov, Paleorthid, Pkravchenko, Siebrand, Wknight94, 4 anonymous edits File:Pangea animation 03.gif  Source: http://en.wikipedia.org/w/index.php?title=File:Pangea_animation_03.gif  License: Public Domain  Contributors: Original by File:Milankovitch Variations sv.png 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Gabbe, Geagea, Moni3, Nickshanks, Ranveig, Roke, The Red Hat of Pat Ferrick, Timeshifter, Valentinian, W!B:, 8 anonymous edits File:UN General Assembly.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:UN_General_Assembly.jpg  License: GNU Free Documentation License  Contributors: Duesentrieb, EvilSuggestions, Gryffindor, Kjetil r, Quasipalm, Ranveig, Xnatedawgx, Yonatanh File:Pyramide Comores.PNG  Source: http://en.wikipedia.org/w/index.php?title=File:Pyramide_Comores.PNG  License: Creative Commons Attribution 2.5  Contributors: :fargomeD File:ReligionSymbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:ReligionSymbol.svg  License: GNU Free Documentation License  Contributors: :Mouagip File:US-hoosier-family.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:US-hoosier-family.jpg  License: Creative Commons Attribution 2.0  Contributors: :Tysto File:RERParisVision2025.png  Source: http://en.wikipedia.org/w/index.php?title=File:RERParisVision2025.png  License: Creative Commons Attribution-Sharealike 2.5  Contributors: ALE!, Alno, Cacophony, Chumwa, Clicsouris, EvaK, GeorgHH, Jcornelius, Juiced lemon, Lokal Profil, Norro, Olivier2, Pabix, Pegship, Pline, Smiley.toerist, 3 anonymous edits File:Tourists-2-x.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Tourists-2-x.jpg  License: GNU Free Documentation License  Contributors: :Beyond silence File:New-York-Jan2005.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:New-York-Jan2005.jpg  License: GNU Free Documentation License  Contributors: Bernd Untiedt, Fb78, Quasipalm File:Geabios3d.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Geabios3d.jpg  License: unknown  Contributors: Gap, Mdd File:Alexander von Humboldt-selfportrait.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Alexander_von_Humboldt-selfportrait.jpg  License: Public Domain  Contributors: :Avatar File:The Geographer.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:The_Geographer.jpg  License: Public Domain  Contributors: AndreasPraefcke, Ecummenic, Hkgeogphr, Jaranda, Mattes, Melkom, Plindenbaum, Shakko, Vincent Steenberg File:Lake Hawea, New Zealand.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Lake_Hawea,_New_Zealand.jpg  License: Public Domain  Contributors: Original er was Yogi de at en.wikipedia Image:glacier.zermatt.arp.750pix.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Glacier.zermatt.arp.750pix.jpg  License: unknown  Contributors: Saperaud, ZorkNika, 1 anonymous edits Image:YosemiteFromPlane.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:YosemiteFromPlane.JPG  License: GNU Free Documentation License  Contributors: Qfl247 (talk). Original er was Qfl247 at en.wikipedia. Later version(s) were ed by Graeme Bartlett at en.wikipedia. File:Atmosphere composition diagram.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Atmosphere_composition_diagram.jpg  License: Public Domain  Contributors: US CLIMATE CHANGE SCIENCE PROGRAM OFFICE File:El Nino regional impacts.gif  Source: http://en.wikipedia.org/w/index.php?title=File:El_Nino_regional_impacts.gif  License: Public Domain  Contributors: NOAA File:Top of Atmosphere.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Top_of_Atmosphere.jpg  License: Public Domain  Contributors: NASA Earth Observatory

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