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Encyclopedia > Earth
Earth

Famous "Blue Marble" photograph of Earth, taken from Apollo 17.
Orbital characteristics
Epoch J2000
Aphelion 152,097,701 km
1.0167103335 AU
Perihelion: 147,098,074 km
0.9832898912 AU
Semi-major axis: 149,597,887.5 km
1.0000001124 AU
Eccentricity: 0.016710219
Orbital period: 365.256366 days
1.0000175 yr
Avg. orbital speed: 29.783 km/s
107,218 km/h
Inclination: Reference (0)
7.25° to Sun's equator
Longitude of ascending node: 348.73936°
Argument of perihelion: 114.20783°
Satellites: 1 (the Moon)
Physical characteristics
Flattening: 0.0033528 [1]
Circumference: 40,075.02 km (equatorial)
40,007.86 km (meridional)
40,041.47 km (mean)
Surface area: 510,065,600 km²

148,939,100 km² land  (29.2 %)

361,126,400 km² water (70.8 %)
Volume: 1.0832073×1012 km³
Mass: 5.9736×1024 kg
Mean density: 5,515.3 kg/m³
Equatorial surface gravity: 9.780327 m/s²[3]
0.99732 g
Escape velocity: 11.186 km/s
40,270 km/h
Sidereal rotation period: 0.997258 d
23h 56m 04.09054s[3]
Rotation velocity at equator: 465.11 m/s
Axial tilt: 23.439281°
Albedo: 0.367
Surface temp.:
Kelvin
Celsius
min mean max
185 K 287 K 331 K
-88.3 °C 14 °C 57.7 °C
Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly
Atmosphere
Surface pressure: 101.3 kPa (MSL)
Composition: 78.08% N2
20.95% O2
0.93% Argon
0.038% Carbon dioxide
Trace water vapor (varies with climate)

Earth (IPA: /ɜrθ/) is the third planet from the Sun and is the largest of the terrestrial planets in the Solar System, in both diameter and mass. It is also referred to as the Earth, Planet Earth, Gaia, Terra,[4] and "the World". For other uses, see Volume (disambiguation). ... For other uses, see Mass (disambiguation). ... For other uses, see Density (disambiguation). ... The surface gravity of a Killing horizon is the acceleration, as exerted at infinity, needed to keep an object at the horizon. ... Earths gravity, denoted by g, refers to the attractive force that the Earth exerts on objects on or near its surface (or, more generally, objects anywhere in the Earths vicinity). ... Meters per second squared is the SI derived unit of acceleration, defined by distance or displacement in metres divided by time in seconds and again divided by time in seconds. ... The term g force or gee force refers to the symbol g, the force of acceleration due to gravity at the earths surface. ... Space Shuttle Atlantis launches on mission STS-71. ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... Albedo is the ratio of reflected to incident electromagnetic radiation. ... For other uses, see Temperature (disambiguation). ... For other uses, see Kelvin (disambiguation). ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... Terra Mater or Tellus Mater was a goddess personifying the Earth in Roman mythology. ... Diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure at any point in the Earths atmosphere. ... Wikipedia does not yet have an article with this exact name. ... For considerations of sea level change, in particular rise associated with possible global warming, see sea level rise. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... General Name, symbol, number argon, Ar, 18 Chemical series noble gases Group, period, block 18, 3, p Appearance colorless Standard atomic weight 39. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Water vapor or water vapour (see spelling differences), also aqueous vapor, is the gas phase of water. ... This article is about the astronomical term. ... Sol redirects here. ... The inner planets, Mercury, Venus, Earth, and Mars, their sizes to scale. ... This article is about the Solar System. ... DIAMETER is a computer networking protocol for AAA (Authentication, Authorization and Accounting). ... For other uses, see Mass (disambiguation). ... For other uses, see Gaia. ... Terra Mater or Tellus Mater was a goddess personifying the Earth in Roman mythology. ... For other uses, see World (disambiguation). ...

Home to millions of species[5] including humans, Earth is the only place in the universe where life is known to have originated. Scientific theory indicates that the planet formed 4.54 billion years[6][7][8][9] ago, and life appeared on its surface within a billion years. Since then, 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 radiation, permitting life on land. For other uses, see Species (disambiguation). ... This article is about modern humans. ... For other uses, see Universe (disambiguation). ... For other uses, see Life (disambiguation). ... The word theory has a number of distinct meanings in different fields of knowledge, depending on their methodologies and the context of discussion. ... Earth as seen from Apollo 17 Modern geologists consider the age of the Earth to be around 4. ... For other uses, see Biosphere (disambiguation). ... Air redirects here. ... This article or section does not adequately cite its references or sources. ... An aerobic organism or aerobe is an organism that has an oxygen based metabolism. ... The ozone layer is a layer in Earths atmosphere which contains relatively high concentrations of ozone (O3). ... Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ...

Earth's outer surface is divided into several rigid segments, or tectonic plates, that gradually 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; liquid water, necessary for all known life, is not known to exist on any other planet's surface.[10][11] Earth'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 cutaway from core to exosphere. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... // For other uses, see time scale. ... Annual mean sea surface salinity for the World Ocean. ... Animated map exhibiting the worlds oceanic waters. ... Animated, colour-coded map showing the various continents. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Earth cutaway from core to exosphere. ... Earth cutaway from core to exosphere. ...

Earth interacts with other objects in outer space, including the Sun and the Moon. At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis. This length of time is a sidereal year, which is equal to 365.26 solar days.[12] The Earth's axis of rotation is tilted 23.4°[13] away from the perpendicular to its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year. 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. A cometary bombardment during the early history of the planet played a role in the formation of the oceans.[14] Later, asteroid impacts caused significant changes to the surface environment. Long term periodic changes in the Earth's orbit, caused by the gravitational influence of other planets, are believed to have given rise to the ice ages that have intermittently covered significant portions of Earth's surface in glacial sheets. Layers of Atmosphere - not to scale (NOAA)[1] Outer space, sometimes simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. ... Sol redirects here. ... This article is about Earths moon. ... The sidereal year is the time for the Sun to return to the same position in respect to the stars of the celestial sphere. ... Solar time is based on the idea that, when the sun reaches its highest point in the sky, it is noon. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... Fig. ... The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded. ... A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... This article is about tides in the Earths oceans. ... Comet Hale-Bopp Comet West For other uses, see Comet (disambiguation). ... For other uses, see Asteroid (disambiguation). ... Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian civil engineer and mathematician Milutin MilankoviÄ‡. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ...

## History

Main article: History of Earth

Scientists have been able to reconstruct detailed information about the planet's past. Earth and the other planets in the Solar System formed 4.54 billion years ago[6] out of the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun. 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 soon afterwards, possibly as the result of a Mars-sized object (sometimes called Theia) with about 10% of the Earth's mass[15] impacting the Earth in a glancing blow.[16] 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 form the Moon. Geological time put in a diagram called a geological clock, showing the relative lengths of the eons of the Earths history. ... This article is about the Solar System. ... This article or section does not cite any references or sources. ... Physics In physics, melting is the process of heating a solid substance to a point (called melting point) where it turns liquid. ... The Big Splash. ... This article is about Earths moon. ...

Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered by comets, produced the oceans.[14] The 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.[17] Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station For other uses, see Volcano (disambiguation). ... Water vapor or water vapour (see spelling differences), also aqueous vapor, is the gas phase of water. ... Comet Hale-Bopp Comet West For other uses, see Comet (disambiguation). ... There are various popular theories as to how the worlds oceans were formed over the past 4. ... Last universal ancestor (LUA), the hypothetical latest living organism from which all currently living organisms descend. ...

The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and resulted in 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.[18] 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.[19] The leaf is the primary site of photosynthesis in plants. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... For other uses, see Ozone (disambiguation). ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance transparent (gas) very pale blue (liquid) Atomic mass 15. ... It has been suggested that Proto-mitochondrion be merged into this article or section. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... The ozone layer is a layer in Earths atmosphere which contains relatively high concentrations of ozone (O3). ...

As the surface continually reshaped itself, over hundreds of millions of years, continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 million years ago (mya), the earliest known supercontinent, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 mya, then finally Pangaea, which broke apart 180 mya.[20] In geology, a supercontinent is a land mass comprising more than one continental core, or craton. ... Depiction of Rodinia at time of initial breakup. ... Pannotia is the name given to a hypothetical supercontinent that existed from about 600 to about 540 mya. ... For other uses, see Pangaea (disambiguation). ...

Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 mya, 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.[21] This article is about the geological formation. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... One computer simulation of conditions during the Snowball Earth period. ... The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ...

Following the Cambrian explosion, about 535 mya, there have been five mass extinctions.[22] The last extinction event occurred 65 mya, when a meteorite collision probably triggered the extinction of the (non-avian) dinosaurs and other large reptiles, but spared small animals such as mammals, which then resembled shrews. Over the past 65 million years, mammalian life has diversified, and several mya, an African ape-like animal gained the ability to stand upright.[23] This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had,[24] affecting both the nature and quantity of other life forms. The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ... An extinction event (also known as: mass extinction; extinction-level event, ELE) occurs when there is a sharp decrease in the number of species in a relatively short period of time. ... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ... Subclasses & Infraclasses Subclass â€ Allotheria* Subclass Prototheria Subclass Theria Infraclass â€ Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the presence of sweat glands, including those that produce milk, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex...

The present pattern of ice ages began about 40 mya, then intensified during the Pleistocene about 3 mya. The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 years. The last ice age ended 10,000 years ago.[25] Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... The Pleistocene epoch (IPA: ) on the geologic timescale is the period from 1,808,000 to 11,550 years BP. The Pleistocene epoch had been intended to cover the worlds recent period of repeated glaciations. ...

## 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, both in terms of size and mass. Of these four planets, Earth also has the highest density, the highest surface gravity and the strongest magnetic field.[26] The inner planets, Mercury, Venus, Earth, and Mars, their sizes to scale. ... This article does not cite any references or sources. ... For other uses, see Jupiter (disambiguation). ... The surface gravity of a Killing horizon is the acceleration, as exerted at infinity, needed to keep an object at the horizon. ... Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ...

### Shape

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

The rotation of the Earth creates the equatorial bulge so that the equatorial diameter is 43 km larger than the pole to pole diameter.[29] The largest local deviations in the rocky surface of the Earth are Mount Everest (8,848 m above local sea level) and the Mariana Trench (10,911 m below local sea level). Hence compared to a perfect ellipsoid, the Earth has a tolerance of about one part in about 584, or 0.17%, which is less than the 0.22% tolerance allowed in billiard balls.[30] Because of the bulge, the feature farthest from the center of the Earth is actually Mount Chimborazo in Ecuador.[31] This article is about rotation as a movement of a physical body. ... An equatorial bulge is a planetological term which describes a bulge which a planet may have around its equator, distorting it into an oblate spheroid. ... â€œEverestâ€ redirects here. ... For considerations of sea level change, in particular rise associated with possible global warming, see sea level rise. ... This article is about the geographical feature. ... 3D rendering of an ellipsoid In mathematics, an ellipsoid is a type of quadric that is a higher dimensional analogue of an ellipse. ... Tolerance in Final Fantasy is an allowance, given as a permissible range, in the nominal dimension or value specification of a manufactured object. ... A close-up picture of American-style pool balls Billiard balls are used in cue sports, such as carom billiards, pool, and snooker. ... The inactive stratovolcano Chimborazo is Ecuadors highest summit. ...

### Chemical composition

F. W. Clarke's Table of Crust Oxides
Compound Formula Composition
silica SiO2 59.71%
alumina Al2O3 15.41%
lime CaO 4.90%
Magnesia MgO 4.36%
sodium oxide Na2O 3.55%
iron(II) oxide FeO 3.52%
potassium oxide K2O 2.80%
iron(III) oxide Fe2O3 2.63%
water H2O 1.52%
titanium dioxide TiO2 0.60%
phosphorus pentoxide P2O5 0.22%
Total 99.22%

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.[32] The abundance of a chemical element measures how relatively common the element is, or how much of the element there is by comparison to all other elements. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ... Calcium oxide (CaO), commonly known as lime, quicklime or burnt lime, is a widely used chemical compound. ... Periclase occurs naturally in contact metamorphic rocks and is a major component of most basic refractory bricks. ... Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses. ... Iron(II) oxide, also called ferrous oxide, is a black-colored powder with the chemical formula FeO. It consists of the element iron in the oxidation state of 2 bonded to oxygen. ... Potassium oxide is a compound of potassium and oxygen used mainly as a intermediate in inorganic synthesis. ... Iron(III) oxide â€” also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust â€” is one of the several oxide compounds of iron, and has paramagnetic properties. ... H2O and HOH redirect here. ... Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. ... Phosphorus pentoxide, perhaps more accurately diphosphorus pentoxide, is so called because of its empirical formula P2O5, as should be expected of any element in oxidation number +5. ... For other uses, see Mass (disambiguation). ... For other uses, see Iron (disambiguation). ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Not to be confused with Silicone. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... This article is about the chemical element. ... For other uses, see Nickel (disambiguation). ... For other uses, see Calcium (disambiguation). ... Aluminum redirects here. ... // Dyamical mass segregation is the process by which heavier members of a gravitationally bound system, such as a star cluster or cluster of galaxies, tend to move toward the center, while lighter members tend to move farther away from the center. ...

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.[33] Frank Wigglesworth With Colleagues Frank Wigglesworth Clarke (1847-1931), was a chemist, born in Boston, Massachusetts 19 March 1847. ... Earth cutaway from core to exosphere. ...

### Internal structure

Earth cutaway from core to exosphere. Not to scale.

The interior of the Earth, like that of the other terrestrial planets, is chemically divided into layers. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. 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.[34] Earth cutaway from core to exosphere. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... A terrestrial planet or telluric planet is a planet which is primarily composed of silicate rocks. ... A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ... The silicate minerals make up the largest and most important class of rock-forming minerals. ... Earth cutaway from core to exosphere. ... Earth cutaway from core to exosphere. ... Earth cutaway from core to exosphere. ... Ordovician ophiolite in Gros Morne National Park, Newfoundland. ...

The geologic component layers of the Earth[35] are at the following depths below the surface:[36]

Depth
km
Layer Density
g/cm³
0–60 Lithosphere (locally varies between 5 and 200 km)
0–35 ... Crust (locally varies between 5 and 70 km) 2.2–2.9
35–60 ... Uppermost part of 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

The internal heat of the planet is most likely produced by the radioactive decay of potassium-40, uranium-238 and thorium-232 isotopes. All three have half-life decay periods of more than a billion years.[37] At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa.[38] 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.[39] The tectonic plates of the Lithosphere on Earth. ... Earth cutaway from core to exosphere. ... Earth cutaway from core to exosphere. ... This article does not cite any references or sources. ... Earth cutaway from core to exosphere. ... General Name, symbol, number potassium, K, 19 Chemical series alkali metals Group, period, block 1, 4, s Appearance silvery white Standard atomic weight 39. ... General Name, symbol, number uranium, U, 92 Chemical series actinides Group, period, block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Standard atomic weight 238. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Standard atomic weight 232. ... For other uses, see Isotope (disambiguation). ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... The initials GPA can refer, among other things, to Grade Point Average; see Grade (education) Guinness Peat Aviation General Practice Australia, a private, independent medical accreditation society Greyhound Pets of America This is a disambiguation page &#8212; a navigational aid which lists other pages that might otherwise share the same... A lava lamp illustrates the basic concept of a mantle plume. ... In geology, a hotspot is a location on the Earths surface that has experienced active volcanism for a long period of time. ... Moses Coulee showing multiple flood basalt flows of the Columbia River Basalt Group. ...

### Tectonic plates

Main article: Plate tectonics
A map illustrating the Earth's major plates.

According to plate tectonics theory, the outermost part of the Earth's interior is made up of two layers: the lithosphere, comprising the crust, and the solidified uppermost part of the mantle. Below the lithosphere lies the asthenosphere, which forms the inner part of the mantle. The asthenosphere behaves like a superheated and extremely viscous liquid.[40] The tectonic plates of the world were mapped in the second half of the 20th century. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... The tectonic plates of the Lithosphere on Earth. ... Earth cutaway from core to exosphere. ... Earth cutaway from core to exosphere. ... This article does not cite any references or sources. ... Viscosity is a measure of the resistance of a fluid to deformation under shear stress. ...

The lithosphere essentially floats on the asthenosphere and is broken up into what are called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: convergent, divergent and transform. The last occurs where two plates move laterally relative to each other, creating a strike-slip fault. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur along these plate boundaries.[41] Global earthquake epicentres, 1963â€“1998 The 14 major plates plus the Scotia Plate Plate tectonics map from NASA This is a list of tectonic plates on Earth. ... In plate tectonics, a convergent boundary (convergent fault boundary, convergent plate boundary, or active margin) is where two tectonic plates slide towards each other and usually collide forming either a subduction zone with its associated island arc or an orogenic belt and associated mountain range. ... In plate tectonics, a divergent boundary (divergent fault boundary or divergent plate boundary), (but also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two tectonic plates that are moving away from each other. ... In plate tectonics, a transform boundary (also known as transform fault boundary, transform plate boundary, transform plate margin, slip boundary or conservative plate boundary) is said to occur when tectonic plates slide and grind against each other along a transform fault. ... Old fault exposed by roadcut near Harrisburg, Pennsylvania. ... This article is about the natural seismic phenomenon. ... Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station For other uses, see Volcano (disambiguation). ... // Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within... The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. ...

The main plates are:[42]

Plate name Area
106 km²
Covering
African Plate 61.3 Africa
Antarctic Plate 60.9 Antarctica
Australian Plate 47.2 Australia
Eurasian Plate 67.8 Asia and Europe
North American Plate 75.9 North America and north-east Siberia
South American Plate 43.6 South America
Pacific Plate 103.3 Pacific Ocean

Notable minor 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 actually fused with 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[43] (3.0 in/yr) and the Pacific Plate moving 52–69 mm/yr (2.1–2.7 in/yr). At the other extreme, the slowest-moving plate is the Eurasian Plate, progressing at a typical rate of about 21 mm/yr (0.8 in/yr).[44]  The African plate, shown in pinkish-orange The African Plate is a tectonic plate covering the continent of Africa and extending westward to the Mid-Atlantic Ridge. ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... The Antarctic plate is shown in blue on this map The Antarctic Plate is a continental tectonic plate covering the continent of Antarctica and extending outward under the surrounding oceans. ... Categories: Plate tectonics | Geology stubs ...  The Eurasian plate, shown in green The Eurasian Plate is a tectonic plate covering Eurasia (a landmass consisting of the traditional continents of Europe and Asia) except that it does not cover the Indian subcontinent, the Arabian subcontinent, and the area east of the Verkhoyansk Range in East Siberia. ... For other uses, see Asia (disambiguation). ... For other uses, see Europe (disambiguation). ...  The North American plate, shown in brown The North American Plate is a tectonic plate covering most of North America, extending eastward to the Mid-Atlantic Ridge and westward to the Cherskiy Range in East Siberia. ... North America North America is a continent[1] in the Earths northern hemisphere and (chiefly) western hemisphere. ... This article is about Siberia as a whole. ...  The South American plate, shown in purple The South American Plate is a tectonic plate covering the continent of South America and extending eastward to the Mid-Atlantic Ridge. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ...  The Pacific plate, shown in pale yellow The Pacific Plate is an oceanic tectonic plate beneath the Pacific Ocean. ...  The Indian plate, shown in red Due to continental drift, the India Plate split from Madagascar and collided with the Eurasian Plate resulting in the formation of the Himalayas. ... The Arabian plate is shown in bright yellow on this map The Arabian Plate is a continental tectonic plate covering the Arabian peninsula and extending northward to Turkey. ... Detail of tectonic plates from: Tectonic plates of the world. ...  The Nacza plate, shown in light blue The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ...  The Scotia plate, shown in blue-green towards the bottom of the map The Scotia Plate is an oceanic tectonic plate bordering the South American Plate on the north, the South Sandwich microplate to the east, and the Antarctic Plate on the south and west. ...  The Indian plate, shown in red Due to continental drift, the India Plate split from Madagascar and collided with the Eurasian Plate resulting in the formation of the Himalayas. ...  The Cocos plate, shown in gray-blue, off the Pacific coast of Central America The Cocos Plate (Chocos Plate) is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides upon it. ...  The Pacific plate, shown in pale yellow The Pacific Plate is an oceanic tectonic plate beneath the Pacific Ocean. ...  The Eurasian plate, shown in green The Eurasian Plate is a tectonic plate covering Eurasia (a landmass consisting of the traditional continents of Europe and Asia) except that it does not cover the Indian subcontinent, the Arabian subcontinent, and the area east of the Verkhoyansk Range in East Siberia. ...

### Surface

Present day Earth altimetry and bathymetry. Data from the National Geophysical Data Center's TerrainBase Digital Terrain Model.

The Earth's terrain varies greatly from place to place. About 70.8%[45] 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,[29] 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. A landform comprises a geomorphological unit. ... This is a list of lists of extreme points of the world, the points that are farther north, south, east or west than any other locations on the landmasses, continents or countries. ... Image File history File links Size of this preview: 800 Ã— 561 pixel Image in higher resolution (1617 Ã— 1133 pixel, file size: 1. ... Image File history File links Size of this preview: 800 Ã— 561 pixel Image in higher resolution (1617 Ã— 1133 pixel, file size: 1. ... For other uses, see Terrain (journal). ... Bathymetry is the underwater equivalent to topography. ... The National Geophysical Data Center (NGDC) provides scientific stewardship, products and services for geophysical data describing the solid earth, marine, and solar-terrestrial environment, as well as earth observations from space. ...  Sediment  Rock  Mantle  The global continental shelf, highlighted in cyan The continental shelf is the extended perimeter of each continent, which is covered during interglacial periods such as the current epoch by relatively shallow seas (known as shelf seas) and gulfs. ... Oceanic Ridge Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches. ... Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station For other uses, see Volcano (disambiguation). ... The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. ... A Submarine canyon is a steep-sided valley on the seafloor of the continental slope. ... An oceanic plateau is an undersea large igneous province, the equivalent of continental flood basalts such as the Deccan Traps in India and the Snake River Plain in the Pacific Northwest of the United States. ... Abyssal plains are flat or very gently sloping areas of the deep ocean basin floor. ... Mount Cook, a mountain in New Zealand A mountain is a landform that extends above the surrounding terrain in a limited area. ... A dune in the Egyptian desert In geography, a desert is a landscape form or region that receives little precipitation. ... In geography, a plain is a large area of land with relatively low relief. ... For other uses, see Plateau (disambiguation). ... Surface of the Earth Geomorphology is the study of landforms, including their origin and evolution, and the processes that shape them. ...

The planetary surface undergoes reshaping over geological time periods due to the effects 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[46] also act to reshape the landscape. For morphological image processing operations, see Erosion (morphology). ... Weathering is the decomposition of rocks, soils and their minerals through direct contact with the Earths atmosphere. ... A glaciation (a created composite term meaning Glacial Period, referring to the Period or Era of, as well as the process of High Glacial Activity), often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ... Many stretches of the coastline of East Anglia, England, are prone to high rates of erosion, as illustrated by this collapsed section of the cliffs at Hunstanton, Norfolk. ... Some of the biodiversity of a coral reef, in this case the Great Barrier Reef, Australia. ...

As the continental plates migrate across the planet, the ocean floor is subducted under the leading edges. At the same time, upwellings of mantle material create a divergent boundary along mid-ocean ridges. The combination of these processes continually recycles the ocean plate material. Most of the ocean floor is less than 100 million years in age. The oldest ocean plate is located in the Western Pacific, and has an estimated age of about 200 million years. By comparison, the oldest fossils found on land have an age of about 3 billion years.[47][48] The Juan de Fuca plate sinks below the North America plate at the Cascadia subduction zone. ... In plate tectonics, a divergent boundary (divergent fault boundary or divergent plate boundary), (but also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two tectonic plates that are moving away from each other. ... Oceanic Ridge Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches. ...

The continental plates consist 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.[49] 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.[50] The third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types 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.[51] Common carbonate minerals include calcite (found in limestone), aragonite and dolomite.[52] Volcanic rock on North America Plutonic rock on North America Igneous rocks (etymology from latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... For other uses, see granite (disambiguation). ... A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. ... For the cities, see Basalt, Colorado and Basalt, Idaho. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... For other uses, see Quartz (disambiguation). ... This article does not cite any references or sources. ... For the logical fallacy, see Amphibology. ... Rock with mica Mica sheet Mica flakes The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... For other uses, see Limestone (disambiguation). ... Aragonite Aragonite is a polymorph of the mineral calcite, both having the chemical composition CaCO3. ... For other uses, see Dolomite (disambiguation). ...

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% supporting permanent crops.[53] 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.[54] The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland Soil is a complex mixture of materials, principally ground up rock and water. ... Pedogenesis or soil evolution (formation) is the process by which soil is created. ... The tectonic plates of the Lithosphere on Earth. ... Air redirects here. ... The movement of water around, over, and through the Earth is called the water cycle, a key process of the hydrosphere. ... For other uses, see Biosphere (disambiguation). ...

Elevation histogram of the surface of the Earth — approximately 71% of the Earth's surface is covered with water.

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 686 m.[55] Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... For the histogram used in digital image processing, see Color histogram. ... The Dead Sea (â€Ž, yam ha-melaÄ§, Sea of Salt; Quranic Arabic: , baÄ§ráµ˜ l- mayitâ± [3], Death Sea) is a salt lake between the West Bank and Israel to the west, and Jordan to the east. ... â€œEverestâ€ redirects here. ...

### Hydrosphere

Main article: 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 m.[56][57] The average depth of the oceans is 3,794 m, more than five times the average height of the continents.[55] The movement of water around, over, and through the Earth is called the water cycle, a key process of the hydrosphere. ... Ocean (Okeanos, a Greek god of sea and water; Greek &#969;&#954;&#949;&#945;&#957;&#972;&#962;) covers almost three quarters (71%) of the surface of the Earth. ... This article is about the geographical feature. ...

The mass of the oceans is approximately 1.35×1018 metric tons, or about 1/4400 of the total mass of the Earth, and occupies a volume of 1.386×109 km³. If all of the land on Earth were spread evenly, water would rise to an altitude of more than 2.7 km.[58] About 97.5% of the water is saline, while the remaining 2.5% is fresh water. The majority of the fresh water, about 68.7%, is currently in the form of ice.[59] A tonne (also called metric ton) is a non-SI unit of mass, accepted for use with SI, defined as: 1 tonne = 103 kg (= 106 g). ...

About 3.5% of the total mass of the oceans consists of salt. Most of this salt was released from volcanic activity or extracted from cool, igneous rocks.[60] The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms.[61] Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir.[62] Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño-Southern Oscillation.[63] For other uses, see Salt (disambiguation). ... In thermodynamics a heat reservoir is considered as a constant temperature source. ... This article is about the global coupled ocean-atmosphere phenomenon. ...

### Atmosphere

Main article: Earth's atmosphere

The atmospheric pressure on the surface of the Earth averages 101.325 kPa, with a scale height of about 8.5 km.[64] It is 78% nitrogen and 21% oxygen, with trace amounts of water vapor, carbon dioxide and other gaseous molecules. Air redirects here. ... Diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure at any point in the Earths atmosphere. ... Wikipedia does not yet have an article with this exact name. ... A scale height is a term often used in scientific contexts for a distance over which a quantity decreases by a factor of e. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ...

Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 billion years ago, forming the primarily nitrogen-oxygen atmosphere that exists today. This change enabled the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life on Earth's include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature.[65] 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.[45] For other uses, see Biosphere (disambiguation). ... For other uses, see Atmosphere (disambiguation). ... Oxygen evolution is the process of generating molecular oxygen through chemical reaction. ... The Oxygen Catastrophe was a massive environmental change believed to have happened during the Siderian period at the beginning of the Paleoproterozoic era. ... For other uses, see Atmosphere (disambiguation). ... An aerobic organism or aerobe is an organism that has an oxygen based metabolism. ... The ozone layer is a layer in Earths atmosphere which contains relatively high concentrations of ozone (O3). ... Magnetic field lines shown by iron filings In physics, the space surrounding moving electric charges, changing electric fields and magnetic dipoles contains a magnetic field. ... For other uses, see Ultraviolet (disambiguation). ... Solar irradiance spectrum at top of atmosphere. ... Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ... Wikinews has related news: Scientists warn thawing Siberia may trigger global meltdown A schematic representation of the exchanges of energy between outer space, the Earths atmosphere, and the Earth surface. ... Top: Increasing atmospheric CO2 levels as measured in the atmosphere and ice cores. ...

#### Weather and climate

Main articles: 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 (about 7 mi) 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.[66] For the geological process, see Weathering or Erosion. ... Atmosphere diagram showing the mesosphere and other layers. ... Atmospheric circulation is the large-scale movement of air, and the means (together with the ocean circulation, which is smaller [1]) by which heat is distributed on the surface of the Earth. ... For the geological process, see Weathering or Erosion. ...

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°.[67] 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.[68] The trade winds are a pattern of wind found in bands around Earths equatorial region. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses IlhÃ©u das Rolas, in SÃ£o TomÃ© and PrÃ­ncipe. ... The Westerlies are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. ... A simplified summary of the path of the Thermohaline Circulation. ...

Source regions of global air masses.

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.[66] Most of the water is then transported back to lower elevations by river systems, usually returning to the oceans or being deposited into lakes. This water cycle is a vital mechanism for supporting 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.[69] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... In meteorology, an air mass is a large volume of air having fairly uniform characteristics of temperature, atmospheric pressure, and water vapor content. ... For other uses, see River (disambiguation). ... For other uses, see Lake (disambiguation). ... The movement of water around, over, and through the Earth is called the water cycle. ... Atmospheric circulation is the large-scale movement of air, and the means (together with the ocean circulation, which is smaller [1]) by which heat is distributed on the surface of the Earth. ...

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.[70] 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.[67] World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses IlhÃ©u das Rolas, in SÃ£o TomÃ© and PrÃ­ncipe. ... A noontime scene from the Philippines on a day when the Sun is almost directly overhead. ... The subtropics are the zones of the Earth immediately north and south of the tropic zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitude 23. ... For the usage in virology, see temperate (virology). ... Location of the polar regions Northern Hemisphere permafrost (permanently frozen ground) in purple. ... In meteorology, an air mass is a large volume of air having fairly uniform characteristics of temperature, atmospheric pressure, and water vapor content. ... The KÃ¶ppen climate classification is one of the most widely used climate classification systems. ... Wladimir Peter KÃ¶ppen (September 25, 1846 in Saint Petersburg, Russia â€” June 22, 1940 in Graz, Austria) was a German geographer, meteorologist, climatologist and botanist. ... This article is about arid terrain. ... Regions containing a continental climate exist in portions of Northern Hemisphere continents, and also at higher elevations in certain other parts of the world. ...

#### Upper atmosphere

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

Above the troposphere, the atmosphere is usually divided into the stratosphere, mesosphere, and thermosphere.[65] Each of these layers 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).[71] An important part of the atmosphere for life on Earth is the ozone layer, a component of the stratosphere that partially shields the surface from ultraviolet light. The Kármán line, defined as 100 km above the Earth's surface, is a working definition for the boundary between atmosphere and space.[72] Image File history File links Size of this preview: 800 Ã— 532 pixel Image in higher resolution (3072 Ã— 2041 pixel, file size: 478 KB, MIME type: image/jpeg) S103-E-5037 (21 December 1999)--- Astronauts aboard the Space Shuttle Discovery recorded this rarely seen phenomenon of the full Moon partially obscured... Image File history File links Size of this preview: 800 Ã— 532 pixel Image in higher resolution (3072 Ã— 2041 pixel, file size: 478 KB, MIME type: image/jpeg) S103-E-5037 (21 December 1999)--- Astronauts aboard the Space Shuttle Discovery recorded this rarely seen phenomenon of the full Moon partially obscured... Layers of Atmosphere - not to scale (NOAA)[1] Outer space, sometimes simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. ... Atmosphere diagram showing stratosphere. ... The mesosphere (from the Greek words mesos = middle and sphaira = ball) is the layer of the Earths atmosphere that is directly above the stratosphere and directly below the thermosphere. ... The thermosphere is the layer of the earths atmosphere directly above the mesosphere and directly below the exosphere. ... The lapse rate is defined as the negative of the rate of change in an atmospheric variable, usually temperature, with height observed while moving upwards through an atmosphere. ... [fAgot png|thumb|200px|right|Atmosphere diagram showing the exosphere and other layers. ... A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ... The plasma in the solar wind meeting the heliopause The solar wind is a stream of charged particles (i. ... This article is about the tv programme Life on Earth. ... The ozone layer is a layer in Earths atmosphere which contains relatively high concentrations of ozone (O3). ... Layers of Atmosphere - not to scale (NOAA)[1] Atmospheric gases scatter blue wavelengths of visible light more than other wavelengths, giving the Earthâ€™s visible edge a blue halo. ...

Due to thermal energy, 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.[73] For this reason, the Earth's current environment is oxidizing, rather than reducing, with consequences for the chemical nature of life which developed on the planet. The oxygen-rich atmosphere also preserves much of the surviving hydrogen by locking it up in water molecules.[74] Space Shuttle Atlantis launches on mission STS-71. ... There are several different processes that can lead to the escape of a planetary atmosphere. ... This article is about the chemistry of hydrogen. ... Space Shuttle Atlantis launches on mission STS-71. ... Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ... For other uses, see Life (disambiguation). ...

The Earth's magnetic field, which approximates a dipole.

Dipole field from NASA. Copied from http://geomag. ... Dipole field from NASA. Copied from http://geomag. ... The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ...

### 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. 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 in nature, and 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.[75][76] The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... This article is about the electromagnetic phenomenon. ... The Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. ... Recent geomagnetic reversals. ...

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.[77]
A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ... The plasma in the solar wind meeting the heliopause The solar wind is a stream of charged particles (i. ... In a planetary magnetosphere, the bow shock is the boundary at which the solar wind abruptly drops as a result of its approach to the magnetopause. ... Van Allen radiation belts The Van Allen Radiation Belt is a torus of energetic charged particles (plasma) around Earth, held in place by Earths magnetic field. ... In geometry, a torus (pl. ... In physics, a charged particle is a particle with an electric charge. ... For other uses, see Plasma. ... The Aurora Borealis, or Northern Lights, shines above Bear Lake Aurora Borealis as seen over Canada at 11,000m (36,000 feet) Red and green Aurora in Fairbanks, Alaska Aurora Borealis redirects here. ...

## Orbit and rotation

Main article: Earth rotation
An animation showing the rotation of the Earth.

Relative to the background stars, it takes the Earth, on average, 23 hours, 56 minutes and 4.091 seconds (one sidereal day) to rotate around the axis that connects the north and the south poles.[78] From Earth, the main apparent motion of celestial bodies in the sky (except that of meteors within the atmosphere and low-orbiting satellites) is to the west at a rate of 15°/h = 15'/min. This is equivalent to an apparent diameter of the Sun or Moon every two minutes. (The apparent sizes of the Sun and the Moon are approximately the same.) The Earths rotation is the rotation of the solid earth around its own axis, which is called Earths axis or rotation axis. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... The axis of rotation of a rotating body is a line such that the distance between any point on the line and any point of the body remains constant under the rotation. ... For other uses, see North Pole (disambiguation). ... For other uses, see South Pole (disambiguation). ... Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ...

Earth orbits the Sun at an average distance of about 150 million kilometers (93.2 million miles) every 365.2564 mean solar days (1 sidereal year). From Earth, this gives an apparent movement of the Sun with respect to the stars at a rate of about 1°/day (or a Sun or Moon diameter every 12 hours) eastward. 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 or 67,000 mi/h), which is fast enough to cover the planet's diameter (about 12,600 km [7,800 mi]) in seven minutes, and the distance to the Moon (384,000 km or 238,000 mi) in four hours.[64] The sidereal year is the time for the Sun to return to the same position in respect to the stars of the celestial sphere. ... Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ... This article is about the astronomical concept. ...

Earth seen as a tiny dot by the Voyager 1 spacecraft, more than 6 billion kilometers (4 billion miles) from Earth.

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. 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 (which causes the seasons); 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).[79][64] This is the Pale Blue Dot photograph of the Earth taken by the Voyager 1 spacecraft. ... This is the Pale Blue Dot photograph of the Earth taken by the Voyager 1 spacecraft. ... Seen from four billion miles away, Earth is a dot obscured in a beam of scattered sunlight (pinpointed by artificial blue circle). ... For the album by The Verve, see Voyager 1 (album). ... This article is about Earths moon. ... In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it was concentrated. ... In Egyptian mythology, Month is an alternate spelling for Menthu. ... The two celestial poles are the imaginary points where the Earths spin axis intersects the imaginary rotating sphere of gigantic radius, called the celestial sphere. ... A clockwise motion is one that proceeds like the clocks hands: from the top to the right, then down and then to the left, and back to the top. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... This article or section is in need of attention from an expert on the subject. ... Time lapse movie of the 3 March 2007 lunar eclipse A lunar eclipse occurs whenever the Moon passes through some portion of the Earths shadow. ... Photo taken during the 1999 eclipse. ...

Because of the axial tilt of the Earth, the position of the Sun in the sky (as seen by an observer on the surface) varies over the course of the year. For an observer at a northern latitude, when the northern pole is tilted toward the Sun the day lasts longer and the Sun climbs higher in the sky. This results in warmer average temperatures from the increase in solar radiation reaching the surface. When the northern pole is tilted away from the Sun, the reverse is true and the climate is generally cooler. Above the arctic circle, an extreme case is reached where there is no daylight at all for part of the year. (This is called a polar night.) For the fast food restaurant chain, see Arctic Circle Restaurants. ... The polar night is the night lasting more than 24 hours, usually inside the polar circles. ...

This variation in the climate (because of the direction of the Earth's axial tilt) results in the seasons. 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. 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. The axial tilt in the southern hemisphere is exactly the opposite of the direction in the northern hemisphere. Thus the seasonal effects in the south are reversed. This article or section is in need of attention from an expert on the subject. ... â€œSummer solsticeâ€ redirects here. ... For other uses, see Equinox (disambiguation). ... is the 355th day of the year (356th in leap years) in the Gregorian calendar. ... is the 172nd day of the year (173rd in leap years) in the Gregorian calendar. ... is the 79th day of the year (80th in leap years) in the Gregorian calendar. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ...

The angle of the Earth's tilt is relatively stable over long periods of time. However, the tilt does undergo a slight, irregular motion (known as nutation) with a main period of 18.6 years. The orientation (rather than the angle) of the Earth's axis also changes over time, precessing around in a complete circle over each 25,800 year cycle; this precession is the 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.[80] Rotation (green), Precession (blue) and Nutation (red) of the Earth Nutation is a slight irregular motion (etymologically a nodding) in the axis of rotation of a largely axially symmetric object, such as a gyroscope or a planet. ... Precession redirects here. ... A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... An equatorial bulge is a planetological term which describes a bulge which a planet may have around its equator, distorting it into an oblate spheroid. ... This article needs to be wikified. ... In mathematics and theoretical physics, quasiperiodic motion is in rough terms the type of motion executed by a dynamical system containing two incommensurable frequencies. ... The Chandler wobble is a small variation in Earths axis of rotation, discovered by American astronomer Seth Carlo Chandler in 1891. ...

In modern times, Earth's perihelion occurs around January 3, and the aphelion around July 4 (for other eras, see precession and Milankovitch cycles). The changing Earth-Sun distance results in an increase of about 6.9%[81] 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.[82] This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... is the 3rd day of the year in the Gregorian calendar. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... is the 185th day of the year (186th in leap years) in the Gregorian calendar. ... The precession of Earths axis of rotation with respect to inertial space is also called the precession of the equinoxes. ... Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian civil engineer and mathematician Milutin MilankoviÄ‡. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the...

The Hill sphere (gravitational sphere of influence) of the Earth is about 1.5 Gm (930,000 miles) in radius.[83][84] 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. A Hill sphere approximates the gravitational sphere of influence of one astronomical body in the face of perturbations from another heavier body around which it orbits. ... Gravity is a force of attraction that acts between bodies that have mass. ...

## Observation

Earth was first photographed from space by Explorer 6 in 1959.[85] Yuri Gagarin became the first human to view Earth from space in 1961. The crew of the Apollo 8 was the first to view an Earth-rise from lunar orbit in 1968. In 1972 the crew of the Apollo 17 produced the famous "Blue Marble" photograph of the planet Earth (see top of page). NASA archivist Mike Gentry has speculated that "The Blue Marble" is the most widely distributed image in human history. Geocentric orbit refers to the orbit of any object orbiting the Earth, such as the Moon or artificial satellites. ... Explorer 6 was a US satellite launched on August 7, 1959. ... â€œGagarinâ€ redirects here. ... Apollo 8 was the second successful manned mission of the Apollo space program, in which Commander Frank Borman, Command Module Pilot James Lovell and Lunar Module Pilot William Anders became the first humans to orbit around the Moon. ... Apollo 17 was the eleventh manned space mission in the NASA Apollo program. ... The Blue Marble is a famous photograph of the Earth taken on 7 December 1972 by the crew of the Apollo 17 spacecraft at a distance of about 45,000 kilometers or about 28,000 miles. ...

Earth and Moon from Mars, imaged by Mars Global Surveyor.

From space, the Earth can be seen to go through phases similar to the phases of the Moon and Venus. This appearance is caused by light that reflects off the Earth as it moves around the Sun. The phases seen depend upon the observer's location in space, and the rate is determined by their orbital period, and by the orbital period of the Earth itself. The phases of the Earth can be simulated by shining light on a globe of the Earth. Download high resolution version (961x961, 17 KB)Courtesy NASA/JPL/Malin Space Science Systems [1] [2] Image of Earth and Moon, taken by the Mars Orbiter Camera of Mars Global Surveyor on May 8, 2003 at 12:59:58 UTC. South America is visible. ... Download high resolution version (961x961, 17 KB)Courtesy NASA/JPL/Malin Space Science Systems [1] [2] Image of Earth and Moon, taken by the Mars Orbiter Camera of Mars Global Surveyor on May 8, 2003 at 12:59:58 UTC. South America is visible. ... The Mars Global Surveyor (MGS) was a US spacecraft developed by NASA and the Jet Propulsion Laboratory and launched November 1996. ... Layers of Atmosphere - not to scale (NOAA)[1] Outer space, sometimes simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. ... In astronomy, a phase of the Moon is any of the aspects or appearances presented by the Moon as seen from Earth, determined by the portion of the Moon that is visibly illuminated by the Sun. ... Sol redirects here. ...

An observer on Mars would be able to see the Earth go through phases similar to those that an Earth-bound observer sees the phases of Venus (as discovered by Galileo). However, a fictional observer on the Sun would not see the Earth going through phases. The Sun observer would only be able to see the lit side of the Earth. The phases of Venus can be seen without a telescope by those with exeptionally acute eye-sight. ... Galileo can refer to: Galileo Galilei, astronomer, philosopher, and physicist (1564 - 1642) the Galileo spacecraft, a NASA space probe that visited Jupiter and its moons the Galileo positioning system Life of Galileo, a play by Bertolt Brecht Galileo (1975) - screen adaptation of the play Life of Galileo by Bertolt Brecht...

## Moon

Main article: Moon
Name Diameter Mass Semi-major axis Orbital period
Moon 3,474.8 km 7.349×1022 kg 384,400 km 27 days, 7 hours, 43.7 minutes
2,159.2 mi 8.1×1019 (short) tons 238,700 mi

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. (Charon is larger relative to the dwarf planet Pluto.) The natural satellites orbiting other planets are called "moons", after Earth's Moon. This article is about Earths moon. ... The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae. ... This article is about Earths moon. ... The inner planets, Mercury, Venus, Earth, and Mars, their sizes to scale. ... Charon (shair-É™n or kair-É™n (key), IPA , Greek Î§Î¬ÏÏ‰Î½), discovered in 1978, is, depending on the definition employed, either the largest moon of Pluto or one member of a double dwarf planet with Pluto being the other member. ... Artists impression of Pluto (background) and Charon (foreground). ... For other uses, see Pluto (disambiguation). ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ...

The gravitational attraction between the Earth and Moon cause 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. This article is about tides in the ocean. ... Tidal locking makes one side of an astronomical body always face another, like the Moon facing the Earth. ... Lunar phase refers to the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. ... World map with terminator (April) A composite image showing the terminator dividing night from day, running across Europe and Africa. ...

Because of their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm (1.5 in) 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.[86] 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.[87] It has been suggested that Tidal friction be merged into this article or section. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... To help compare orders of magnitude of different times this page lists times between 10âˆ’6 seconds and 10âˆ’5 seconds (1. ... For the Celtic language, see Southwestern Brythonic language; for the residents of the English county, see Devon. ...

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.[88] 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, as it appears to be for Mars. If Earth's axis of rotation were to approach the plane of the ecliptic, extremely severe weather could result from the resulting extreme seasonal differences. One pole would be pointed directly toward the Sun during summer and directly away during winter. Planetary scientists who have studied the effect claim that this might kill all large animal and higher plant life.[89] However, this is a controversial subject, and further studies of Mars—which has a similar rotation period and axial tilt as Earth, but not its large Moon or liquid core—may settle the matter. Paleontology, palaeontology or palÃ¦ontology (from Greek: paleo, ancient; ontos, being; and Î»ÏŒÎ³Î¿Ï‚, logos, knowledge) is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... Torque applied via an adjustable end wrench Relationship between force, torque, and momentum vectors in a rotating system In physics, torque (or often called a moment) can informally be thought of as rotational force or angular force which causes a change in rotational motion. ... Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... Planetary science, also known as planetology or planetary astronomy, is the science of planets, or planetary systems, and the solar system. ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ...

Viewed from Earth, the Moon is just far enough away to have very nearly the same 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. This allows total and annular eclipses to occur on Earth.
Angular size is a measurement of how large or small something is using rotational measurement (degrees of arc, arc_minutes, and arc-seconds). ... A solid angle is the three dimensional analog of the ordinary angle. ... This article is about astronomical eclipses. ...

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

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.[90] Image File history File links Download high resolution version (3966x200, 34 KB) Illustration of Earth and Moon at average distance from each other (semi-major axis) as seen from distant space; comprised of composite images resized using Photoshop. ... Image File history File links Download high resolution version (3966x200, 34 KB) Illustration of Earth and Moon at average distance from each other (semi-major axis) as seen from distant space; comprised of composite images resized using Photoshop. ... The Big Splash. ... Protoplanets are moon-sized planet embryos within protoplanetary discs. ...

Earth has at least two co-orbital satellites, the asteroids 3753 Cruithne and 2002 AA29.[91] Co-orbital satellites are satellites that share the same mean orbit. ... For other uses, see Asteroid (disambiguation). ... 3753 Cruithne (pronounced , Modern Irish ) is an asteroid in orbit around the Sun. ... Asteroid 2002 AA29 (also written 2002 AA29) is a near-Earth asteroid discovered in January 2001 by the LINEAR asteroid survey. ...

## 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.[92] 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 necessary to originate and sustain life on this planet.[93] Understanding planetary habitability is partly an extrapolation of the Earths conditions, as it is the only planet currently known to support life. ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ...

### Biosphere

Main article: 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 in the universe where life is known to exist. Some scientists believe that Earth-like biospheres might be rare.[94] For other uses, see Biosphere (disambiguation). ... For other uses, see Biosphere (disambiguation). ... This article is about evolution in biology. ... The Rare Earth hypothesis is a hypothesis in planetary astronomy and astrobiology which argues that the emergence of complex multicellular life (metazoa) on Earth required an extremely unlikely combination of astrophysical and geological events and circumstances. ...

The biosphere is divided into a number of biomes, inhabited by broadly similar plants and animals. On land primarily latitude and height above the sea level separates biomes. Terrestrial biomes lying within the Arctic, Antarctic Circle or in high altitudes are relatively barren of plant and animal life, while the greatest latitudinal diversity of species is found at the Equator.[95] A biome is a climate and geographical area of ecologically similar communities of plants, animals, and soil organisms, often referred to as ecosystems. ... u fuck in ua ... The word Animals when used alone has several possible meanings in the English language. ... This article is about the geographical term. ... For the fast food restaurant chain, see Arctic Circle Restaurants. ... Zoomable PDF of the map this is based on The Antarctic Circle is one of the five major circles of latitude that mark maps of the Earth. ... For other uses, see Plant (disambiguation). ... For other uses, see Animal (disambiguation). ... // The increase in species richness or biodiversity that occurs from the poles to the tropics, often referred to as the latitudinal gradient in species diversity, is one of the most widely recognized patterns in ecology. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses IlhÃ©u das Rolas, in SÃ£o TomÃ© and PrÃ­ncipe. ...

### Natural resources and land use

Main article: Natural resource

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. Wyoming coal mine. ... Fossil fuels or mineral fuels are hydrocarbons found within the top layer of the earthâ€™s crust. ...

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.[96] These bodies form concentrated sources for many metals and other useful elements. Fossil fuels or mineral fuels are hydrocarbons found within the top layer of the earthâ€™s crust. ... Coal Coal (IPA: ) is a fossil fuel formed in swamp ecosystems where plant remains were saved by water and mud from oxidization and biodegradation. ... Pumpjack pumping an oil well near Lubbock, Texas Ignacy Åukasiewicz - inventor of the refining of kerosene from crude oil. ... This article is about the fossil fuel. ... Burning ice. Methane, released by heating, burns; water drips (USGS). ... This article is about modern humans. ... Iron ore (Banded iron formation) Manganese ore Lead ore Gold ore An ore is a volume of rock containing components or minerals in a mode of occurrence which renders it valuable for mining. ... The various theories of ore genesis explain how the various types of mineral deposits form within the Earths crust. ... For morphological image processing operations, see Erosion (morphology). ... The tectonic plates of the world were mapped in the second half of the 20th century. ... This article is about metallic materials. ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ...

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.[97] Humans also live on the land by using building materials to construct shelters. In 1993, human use of land is approximately: For other uses, see Biosphere (disambiguation). ... For other uses, see Wood (disambiguation). ... Pharmacology (in Greek: pharmacon is drug, and logos is science) is the study of how chemical substances interfere with living systems. ... A coral reef near the Hawaiian islands is an example of a complex marine ecosystem. ... Topsoil is the uppermost layer of soil, usually the top six to eight inches. ... A coral reef near the Hawaiian islands is an example of a complex marine ecosystem. ... Ecological footprint (EF) analysis measures human demand on nature. ... For other kinds of building materials, see Hardware, Biology, Star formation. ... For other uses, see Home (disambiguation). ...

Land use Percentage
Arable land: 13.13%[53]
Permanent crops: 4.71%[53]
Permanent pastures: 26%
Forests and woodland: 32%
Urban areas: 1.5%
Other: 30%

The estimated amount of irrigated land in 1993 was 2,481,250 km².[53]

### Natural and environmental hazards

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. Air pollution Pollution is the introduction of pollutants (whether chemical substances, or energy such as noise, heat, or light) into the environment to such a point that its effects become harmful to human health, other living organisms, or the environment. ... The term acid rain is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. ... // In the dictionary and agriculture, overgrazing is when plants are exposed to grazing for too long, or without sufficient recovery periods. ... This article is about the process of deforestation in the environment. ... Ship stranded by the retreat of the Aral Sea Desertification is the degradation of land in arid, semi arid and dry sub-humid areas resulting from various climatic variations, but primarily from human activities. ... This article does not cite any references or sources. ... For other uses, see Species (disambiguation). ... For other uses, see Extinction (disambiguation). ... Retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. ... For morphological image processing operations, see Erosion (morphology). ... Lantana invasion of abandoned citrus plantation; Moshav Sdey Hemed, Israel The term invasive species refers to a subset of introduced species or non-indigenous species that are rapidly expanding outside of their native range. ...

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 conditions and a global rise in average sea levels.[98] Scientific consensus is the collective judgment, position, and opinion of the community of scientists in a particular field of science at a particular time. ... Global warming refers to the increase in the average temperature of the Earths near-surface air and oceans in recent decades and its projected continuation. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... This article is about the geological formation. ... An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 kmÂ² (19,305 mileÂ²).[1] The only current ice sheets are in Antarctica and Greenland; during the last ice age at Last Glacial Maximum (LGM) the Laurentide ice sheet covered much... Sea level measurements from 23 long tide gauge records in geologically stable environments show a rise of around 20 centimeters per century (2 mm/year). ...

### Human geography

Main article: Human geography

Population density by country, 2006 Human geography is a branch of geography that focuses on the study of patterns and processes that shape human interaction with the environment, with particular reference to the causes and consequences of the spatial distribution of human activity on the Earths surface. ... Image File history File links world map from Wikipedia, colored by myself File links The following pages link to this file: World government User:Pakaran/Kingdom of Wikipedia Federal World Government ...

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.

Earth has approximately 6,600,000,000 human inhabitants.[99] Projections indicate that the world's human population will reach seven billion in 2013 and 9.2 billion[100] in 2050. 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.[101] For other uses, see Oceania (disambiguation). ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... For other uses, see Asia (disambiguation). ... For other uses, see Europe (disambiguation). ... North America North America is a continent[1] in the Earths northern hemisphere and (chiefly) western hemisphere. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Pacific redirects here. ... Pacific redirects here. ... The Atlantic Ocean, not including Arctic and Antarctic regions. ... This article is about the water body. ... The Southern Ocean, also known as the Antarctic Ocean or South Polar Ocean, is the oceanic division completely in Earths southern hemisphere encircling Antarctica, comprising the southernmost waters of the World Ocean south of 60Â° S latitude. ... The Arctic Ocean, located in the southern hemisphere and mostly in the Antarctic south polar region, is the largest of the worlds five major landmassesic divisions and the deepest. ... A map showing countries commonly considered to be part of the Middle East The Middle East is a region comprising the lands around the southern and eastern parts of the Mediterranean Sea, a territory that extends from the eastern Mediterranean Sea to the Persian Gulf. ... West Indies redirects here. ... Map of Central Asia showing three sets of possible boundaries for the region Central Asia located as a region of the world Central Asia is a vast landlocked region of Asia. ... East Asia Geographic East Asia. ... Regions of Asia:  Northern Asia  Central Asia  Western Asia  Southern Asia  Eastern Asia  Southeastern Asia North Asia or Northern Asia is a subregion of Asia. ... Map of South Asia (see note on Kashmir). ... Location of Southeast Asia Southeast Asia is a subregion of Asia. ...  Southwest Asia in most contexts. ... Australasia Australasia is a term variably used to describe a region of Oceania: Australia, New Zealand, and neighbouring islands in the Pacific Ocean. ... Map showing Melanesia. ... Carving from the ridgepole of a MÄori house, ca 1840 Polynesia (from Greek: Ï€Î¿Î»ÏÏ‚ many, Î½á¿†ÏƒÎ¿Ï‚ island) is a large grouping of over 1,000 islands scattered over the central and southern Pacific Ocean. ... For other uses, see Central America (disambiguation). ... Latin America consists of the countries of South America and some of North America (including Central America and some the islands of the Caribbean) whose inhabitants mostly speak Romance languages, although Native American languages are also spoken. ... Northern America is a name for the parts of North America besides Mexico when Mexico is considered as Latin America. ... World map showing the Americas CIA political map of the Americas The Americas are the lands of the Western hemisphere or New World, consisting of the continents of North America[1] and South America with their associated islands and regions. ...  Central Africa  Middle Africa (UN subregion)  Central African Federation (defunct) Central Africa is a core region of the African continent often considered to include: Burundi Central African Republic Chad Democratic Republic of the Congo Rwanda Middle Africa (as used by the United Nations when categorising geographic subregions) is an analogous...  Eastern Africa (UN subregion)  East African Community  Central African Federation (defunct)  geographic, including above East Africa or Eastern Africa is the easternmost region of the African continent, variably defined by geography or geopolitics. ...  Northern Africa (UN subregion)  geographic, including above North Africa or Northern Africa is the northernmost region of the African continent, separated by the Sahara from Sub-Saharan Africa. ... Categories: Africa geography stubs | Southern Africa ...  Western Africa (UN subregion)  Maghreb[1] West Africa or Western Africa is the westernmost region of the African continent. ... Central Europe The Alpine Countries and the VisegrÃ¡d Group (Political map, 2004) Central Europe is the region lying between the variously and vaguely defined areas of Eastern and Western Europe. ... Pre-1989 division between the West (grey) and Eastern Bloc (orange) superimposed on current national boundaries: Russia (dark orange), other countries of the former USSR (medium orange),members of the Warsaw pact (light orange), and other former Communist regimes not aligned with Moscow (lightest orange). ... Northern Europe Northern Europe is the northern part of the European continent. ... Southern Europe is a region of the European continent. ... A current understanding of Western Europe. ... Download high resolution version (2400x1200, 534 KB)Composite image of the Earth at night, created by NASA and NOAA. NASA Description: This image of Earth&#8217;s city lights was created with data from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS). ... Download high resolution version (2400x1200, 534 KB)Composite image of the Earth at night, created by NASA and NOAA. NASA Description: This image of Earth&#8217;s city lights was created with data from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS). ... An artistâ€™s impression showing one of the Block 5D-2 spacecraft in orbit. ... Photography [fÓ™tÉ‘grÓ™fi:],[foÊŠtÉ‘grÓ™fi:] is the process of recording pictures by means of capturing light on a light-sensitive medium, such as a film or electronic sensor. ... Map of countries by population â€” China and India, the only two countries to have a population greater than one billion, together possess more than a third of the worlds population. ... A developing country is a country with low average income compared to the world average. ... For other uses, see Asia (disambiguation). ... Cities with at least a million inhabitants in 2006 An urban area is an area with an increased density of human-created structures in comparison to the areas surrounding it. ... Sign in a rural area in Dalarna, Sweden Qichun, a rural town in Hubei province, China An artists rendering of an aerial view of the Maryland countryside: Jane Frank (Jane Schenthal Frank, 1918-1986), Aerial Series: Ploughed Fields, Maryland, 1974, acrylic and mixed materials on apertured double canvas, 52...

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 desert (14%),[102] high mountains (27%),[103] or other less suitable terrain. The northernmost permanent settlement in the world is Alert, on Ellesmere Island in Nunavut, Canada.[104] (82°28′N) The southernmost is the Amundsen-Scott South Pole Station, in Antarctica, almost exactly at the South Pole. (90°S) This article is about modern humans. ... Animated map exhibiting the worlds oceanic waters. ... This article is about arid terrain. ... For other uses, see Mountain (disambiguation). ... It has been suggested that CFS Alert be merged into this article or section. ... Ellesmere Island, Nunavut, Canada. ... For the Canadian federal electoral district, see Nunavut (electoral district). ... The Amundsen-Scott South Pole Station is a U.S. research station at the South Pole, in Antarctica. ... For other uses, see South Pole (disambiguation). ...

Independent sovereign nations claim all of the planet's land surface, with the exception of some parts of Antarctica. 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. 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. For other uses, see Nation (disambiguation). ... This is an alphabetical list of the sovereign states of the world, including both de jure and de facto independent states. ... A map of UN member states and their dependent territories as recognized by the UN. Regions excluded: Antarctica (regulated by the Antarctic Treaty System), Vatican City (the Holy See is a UN observer), the Palestinian territories (Palestine, represented by the Palestine Liberation Organization, is a UN observer), and Western Sahara... A dependent territory, dependent area or dependency is a territory that does not possess full political independence or sovereignty as a State. ... The table below lists autonomous areas by country. ... This is a list of extant territorial disputes around the world. ... â€œSovereignâ€ redirects here. ... Alexander the Great Philip II of Spain Napoleon Bonaparte For other uses, see World domination (disambiguation). ...

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. It is not, however, a world government. While the U.N. provides a mechanism for international law and, when the consensus of the membership permits, armed intervention,[105] it serves primarily as a forum for international diplomacy. UN and U.N. redirect here. ... For the political science journal, see International Organization. ... This article or section is in need of attention from an expert on the subject. ...

In total, about 400 people have been outside the Earth's atmosphere as of 2004, and, of these, twelve have walked on the Moon. Normally the only humans in space are those on the International Space Station. The station's crew of three people is usually replaced every six months.

## Cultural viewpoint

The first photograph ever taken of an "Earthrise," on Apollo 8.

The name Earth originated from the 8th century Anglo-Saxon word erda, which means ground or soil. In Old English the word became eorthe, then erthe in Middle English.[106] Earth was first used as the name of the planet around 1400.[107] It is the only planet whose name in English is not derived from greco-roman mythology. Download high resolution version (2457x2411, 646 KB) Description The first photograph taken by humans of Earthrise. ... Download high resolution version (2457x2411, 646 KB) Description The first photograph taken by humans of Earthrise. ... Apollo 8 was the second successful manned mission of the Apollo space program, in which Commander Frank Borman, Command Module Pilot James Lovell and Lunar Module Pilot William Anders became the first humans to orbit around the Moon. ... Spaceship Earth is a world view term usually expressing concern over the use of limited resources available on Earth. ... A Gaia theory is a class of scientific models of the biosphere in which life fosters and maintains suitable conditions for itself by affecting Earths environment. ... Old English redirects here. ... Old English (also called Anglo-Saxon[1], Old English: ) is an early form of the English language that was spoken in parts of what is now England and southern Scotland between the mid-fifth century and the mid-twelfth century. ... Middle English is the name given by historical linguistics to the diverse forms of the English language spoken between the Norman invasion of 1066 and the mid-to-late 15th century, when the Chancery Standard, a form of London-based English, began to become widespread, a process aided by the... The bust of Zeus found at Otricoli (Sala Rotonda, Museo Pio-Clementino, Vatican) Greek mythology is the body of stories belonging to the Ancient Greeks concerning their gods and heroes, the nature of the world and the origins and significance of their own cult and ritual practices. ... A head of Minerva found in the ruins of the Roman baths in Bath Roman mythology, the mythological beliefs of the people of Ancient Rome, can be considered as having two parts. ...

The standard astronomical symbol of the Earth consists of a cross circumscribed by a circle. This symbol is known as the wheel cross, sun cross, Odin's cross or Woden's cross. Although it has been used in various cultures for different purposes, it came to represent the compass points, earth and the land. Another version of the symbol is ♁ (a cross on top of a circle); a stylized globus cruciger that was also used as an early astronomical symbol for the planet Earth.[108] Queen Elizabeth II held a globus cruciger, called the Sovereigns Orb, for her coronation portrait in 1953. ...

Earth has often been personified as a deity, in particular a goddess. In many cultures the mother goddess, also called the Mother Earth, is also portrayed as a fertility deity. See also Graha. Look up deity in Wiktionary, the free dictionary. ... For the 1934 film, see, see The Goddess (1934 film). ... A Cucuteni culture statuette, 4th millennium BC. A mother goddess is a goddess, often portrayed as the Earth Mother, who serves as a general fertility deity, the bountiful embodiment of the earth. ... In polytheistic religions and mythologies, a fertility god is a male deity who is responsible for ensuring human fertility. ... Graha (from Sanskrit à¤—à¥à¤°à¤¹ grÃ¡ha -- seizing, laying hold of, holding [1]) is a â€œcosmic marker of influenceâ€ on the living beings of mother Bhumidevi (earth). ...

To the Aztec, Earth was called Tonantzin — "our mother". The Chinese Earth goddess Hou-T'u[109] is similar to Gaia, the Greek goddess personifying the Earth. To Hindus it is called Bhuma Devi, the Goddess of Earth. In Norse mythology, the Earth goddess Jord was the mother of Thor and the daughter of Annar. Ancient Egyptian mythology is different from that of other cultures because Earth is male, Geb, and sky is female, Nut. Aztec is a term used to refer to certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language and who achieved political and military dominance over large parts of Mesoamerica in the 14th, 15th and 16th centuries, a period referred to as the Late post-Classic... In Aztec mythology, Tonantzin was a lunar mother goddess. ... For other uses, see Gaia. ... Bhavna says there are 300 million gods in Hinduism. ... Bhuma Devi or Bhumi Devi or Bhu Devi is the divine wife of Lord Vishnu. ... Norse, Viking or Scandinavian mythology comprises the indigenous pre-Christian religion, beliefs and legends of the Scandinavian peoples, including those who settled on Iceland, where most of the written sources for Norse mythology were assembled. ... Jord was, in Norse mythology, the goddess of the Earth. ... For other uses, see Thor (disambiguation). ... In Norse mythology, according to the Gylfaginning, Annar (Old Norse Annarr second, another) was the father of Jörd Earth by Nótt Night. The form Ónar (Old Norse Ónarr gaping) is found as a variant. ... Egyptian goddess Isis protecting a mummified pharaoh, a late Ptolemic relief from the Philae Temple, which was first built in the thirtieth dynasty, c. ... ... In Egyptian mythology, Nuit or Nut was the sky goddess, in contrast to most other mythologies, which usually have a sky father. ...

In many religions, accounts of creation of the Earth exist, recalling a story involving the creation of the Earth by a supernatural deity or deities. This article does not cite any references or sources. ... Look up deity in Wiktionary, the free dictionary. ...

In the ancient past there were varying levels of belief in a flat Earth, with the Mesopotamian culture portraying the world as a flat disk afloat in an ocean. The spherical form of the Earth was suggested by early Greek philosophers; a belief espoused by Pythagoras. By the Middle Ages — as evidenced by thinkers such as Thomas Aquinas — European belief in a spherical Earth was widespread.[110] Prior to the introduction of space flight, belief in a spherical Earth was based on observations of the secondary effects of the Earth's shape and parallels drawn with the shape of other planets.[111] For the 1984 album by Thomas Dolby, see The Flat Earth. ... Mesopotamian mythology is the collective name given to Sumerian, Akkadian, Assyrian, and Babylonian mythologies from the land between the Tigris and Euphrates rivers in Iraq. ... Wikipedia does not yet have an article with this exact name. ... Pythagoras of Samos (Greek: ; between 580 and 572 BCâ€“between 500 and 490 BC) was an Ionian (Greek) philosopher[1] and founder of the religious movement called Pythagoreanism. ... The Middle Ages formed the middle period in a traditional schematic division of European history into three ages: the classical civilization of Antiquity, the Middle Ages, and modern times, beginning with the Renaissance. ... Saint Thomas Aquinas, O.P.(also Thomas of Aquin, or Aquino; c. ... Medieval artistic representation of a spherical Earth - with compartments representing earth, air, and water (c. ... Currently, the most common technology for space transport is rocket propulsion, which expels matter to provide a net forward thrust. ...

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, to a lesser extent navigation, the determination of position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information. Cartography or mapmaking (in Greek chartis = map and graphein = write) is the study and practice of making maps or globes. ... Surveyor at work with a leveling instrument. ... Table of geography, hydrography, and navigation, from the 1728 Cyclopaedia. ...

The technological developments of the latter half of the 20th century are widely considered to have altered the public's perception of the Earth. Before space flight, the popular image of Earth was of a green world. Science fiction artist Frank R. Paul provided perhaps the first image of a cloudless blue planet (with sharply defined land masses) on the back cover of the July 1940 issue of Amazing Stories, a common depiction for several decades thereafter.[112] Science fiction is a form of speculative fiction principally dealing with the impact of imagined science and technology, or both, upon society and persons as individuals. ... Frank Rudolph Paul (April 18, 1884 - June 29, 1963) was an illustrator of US pulp-magazines in the science fiction field. ... Amazing Stories magazine, sometimes retitled Amazing Science Fiction, began in April 1926, becoming the first science fiction magazine and one of the pioneers of science fiction in the United States. ...

Apollo 17's 1972 "Blue Marble" photograph of Earth from cislunar space became the current iconic image of the planet as a marble of cloud-swirled blue ocean broken by green-brown continents. A photo taken of a distant Earth by Voyager 1 in 1990 inspired Carl Sagan to describe the planet as a "Pale Blue Dot."[113] Earth has also been described as a massive spaceship, with a life support system that requires maintenance,[114] or as having a biosphere that forms one large organism.[115] Apollo 17 was the eleventh manned space mission in the NASA Apollo program. ... The Blue Marble is a famous photograph of the Earth taken on 7 December 1972 by the crew of the Apollo 17 spacecraft at a distance of about 45,000 kilometers or about 28,000 miles. ... Cislunar space (alternatively, cis-lunar space) is the volume within the Moons orbit, or a sphere formed by rotating that orbit. ... For the album by The Verve, see Voyager 1 (album). ... Insert non-formatted text here Carl Edward Sagan (November 9, 1934 â€“ December 20, 1996) was an American astronomer and astrobiologist and a highly successful popularizer of astronomy, astrophysics, and other natural sciences. ... Seen from four billion miles away, Earth is a dot obscured in a beam of scattered sunlight (pinpointed by artificial blue circle). ... The Space Shuttle Discovery as seen from the International Space Station. ... In human spaceflight, the life support system is a group of devices that allow a human being to survive in outer space. ... For other uses, see Biosphere (disambiguation). ... Life on Earth redirects here. ...

Over the past two centuries a growing environmental movement has emerged that is concerned about humankind's effects on the Earth. The key issues of this socio-political movement are the conservation of natural resources, elimination of pollution, and the usage of land. Environmentalists advocate sustainable management of resources and stewardship of the natural environment through changes in public policy and individual behavior. Of particular concern is the large-scale exploitation of non-renewable resources. Changes sought by the environmental movements are sometimes in conflict with commercial interests due to the additional costs associated with managing the environmental impact of those interests.[116] The environmental movement (a term that sometimes includes the conservation and green movements) is a diverse scientific, social, and political movement. ... The conservation movement is a political and social movement that seeks to protect natural resources including plant and animal species as well as their habitat for the future. ... Air pollution Pollution is the introduction of pollutants (whether chemical substances, or energy such as noise, heat, or light) into the environment to such a point that its effects become harmful to human health, other living organisms, or the environment. ... The Earth Day flag includes a NASA photo. ... Look up stewardship in Wiktionary, the free dictionary. ... This article is about the natural environment. ... Wyoming coal mine. ...

## Future

Artist's conception of the remains of artificial structures on the Earth after the Sun enters its red giant phase and swells to roughly 100 times its current size.

The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium ash at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will increase by 10 percent over the next 1.1 billion years (1.1 Gyr), and by 40% over the next 3.5 Gyr.[117] Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the possible loss of the planet's oceans.[118] Risks to civilization, humans and planet Earth are existential risks that would imperil mankind as a whole and/or have major adverse consequences for the course of human civilization, human extinction or even the end of planet Earth. ... Image File history File links Sun_Red_Giant. ... Image File history File links Sun_Red_Giant. ... The solar luminosity, , is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ...

The Earth's increasing surface temperature will accelerate the inorganic CO2 cycle, reducing its concentration to the lethal levels for plants (10 ppm for C4 photosynthesis) in 900 million years. But even if the Sun were eternal and stable, the continued internal cooling of the Earth would have resulted in a loss of much of its atmosphere and oceans (due to lower volcanism).[119] After another billion years the surface water will have completely disappeared.[120] Inorganic chemistry is the branch of chemistry concerned with the properties and reactions of inorganic compounds. ... For the thermonuclear reaction involving carbon that helps power stars, see CNO cycle. ... The parts-per notations are used to denote low concentrations of chemical elements. ... Overview of C4 carbon fixation C4 carbon fixation is one of three methods, along with C3 and CAM photosynthesis, used by land plants to fix carbon dioxide (binding the gaseous molecules to dissolved compounds inside the plant) for sugar production through photosynthesis. ... This article is about volcanoes in geology. ...

The Sun, as part of its solar lifespan, will expand to a red giant in 5.5 Gyr. Models predict that the Sun will expand out to about 99% of the distance to the Earth's present orbit (1 astronomical unit, or AU). However, by that time, the orbit of the Earth may have expanded to about 1.7 AUs because of the diminished mass of the Sun. The planet might thus escape envelopment by the expanded Sun's sparse outer atmosphere, though most (if not all) existing life will have been destroyed by the Sun's proximity to the Earth.[117]
According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... The astronomical unit (AU or au or a. ... The astronomical unit (AU or au or a. ...

## Notes

1. ^ a b c The WGS 84 reference ellipsoid.
2. ^ This is the radius that gives a sphere with the same volume as the WGS 84 reference ellipsoid.
3. ^ a b Yoder, C. F. (1995) p. 12.
4. ^ Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather than for the planet Earth. C.f.:
Blue, Jennifer (July 5, 2007). Descriptor Terms (Feature Types). Gazetteer of Planetary Nomenclature. USGS. Retrieved on 2007-07-05.
5. ^ May, Robert M. (1999). "How many species are there on earth?". Science 241 (4872): 1441-1449. Retrieved on 2007-08-14.
6. ^ a b Dalrymple, G.B. (1991). The Age of the Earth. California: Stanford University Press. ISBN 0-8047-1569-6.
7. ^ Newman, William L. (July 9, 2007). Age of the Earth. Publications Services, USGS. Retrieved on 2007-09-20.
8. ^ Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Geological Society, London, Special Publications 190: 205-221. Retrieved on 2007-09-20.
9. ^ Stassen, Chris (September 10, 2005). The Age of the Earth. The TalkOrigins Archive. Retrieved on 2007-09-20.
10. ^ Other planets in the solar system are either too hot or too cold to support liquid water. However, it is confirmed to have existed on the surface of Mars in the past, and may still appear today. See: Msnbc. "Rover reveals Mars was once wet enough for life", NASA, Marchr 02, 2007. Retrieved on 2007-08-28. Staff. "Simulations Show Liquid Water Could Exist on Mars", University of Arkansas, November 7, 2005. Retrieved on 2007-08-08.
11. ^ As of 2007, water vapor has been detected in the atmosphere of only one extrasolar planet, and it is a gas giant. See: G. Tinetti et al. (July, 2007). "Water vapour in the atmosphere of a transiting extrasolar planet". Nature 448: 169-171.
12. ^ The number of solar days is one less than the number of sidereal days because the orbital motion of the Earth about the Sun results in one additional revolution of the planet about its axis.
13. ^ Ahrens, Global Earth Physics: A Handbook of Physical Constants, p. 8.
14. ^ a b Morbidelli, A.; Chambers, J.; Lunine, J. I.; Petit, J. M.; Robert, F.; Valsecchi, G. B.; Cyr, K. E. (2000). "Source regions and time scales for the delivery of water to Earth". Meteoritics & Planetary Science 35 (6): 1309–1320. Retrieved on 2007-03-06.
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17. ^ Doolittle, W. Ford (February, 2000). "Uprooting the tree of life". Scientific American 282 (6): 90–95.
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34. ^ Tanimoto, Toshiro (1995). in Thomas J. Ahrens: Crustal Structure of the Earth (PDF), Washington, DC: American Geophysical Union. ISBN 0-87590-851-9. Retrieved on 2007-02-03.
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39. ^ Richards, M. A.; Duncan, R. A.; Courtillot, V. E. (1989). "Flood Basalts and Hot-Spot Tracks: Plume Heads and Tails". Science 246 (4926): 103–107. Retrieved on 2007-04-21.
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57. ^ Takuyo measurement; see Mariana Trench for details.
58. ^ The total volume of the Earth's oceans is: 1.4×109 km³. The total surface area of the Earth is 5.1×108 km². So, to first approximation, the average depth would be the ratio of the two, or 2.7 km.
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73. ^ Liu, S. C.; Donahue, T. M. (1974). "The Aeronomy of Hydrogen in the Atmosphere of the Earth". Journal of Atmospheric Sciences 31 (4): 1118–1136. Retrieved on 2007-03-02.
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76. ^ Campbell, Wallace Hall (2003). Introduction to Geomagnetic Fields. New York: Cambridge University Press, p57. ISBN 0521822068.
77. ^ Stern, David P. (July 8, 2005). Exploration of the Earth's Magnetosphere. NASA. Retrieved on 2007-03-21.
78. ^ Fisher, Rick (January, 30, 1996). Astronomical Times. National Radio Astronomy Observatory. Retrieved on 2007-03-21.
79. ^ Williams, David R. (September 1, 2004). Moon Fact Sheet. NASA. Retrieved on 2007-03-21.
80. ^ Fisher, Rick (February 5, 1996). Earth Rotation and Equatorial Coordinates. National Radio Astronomy Observatory. Retrieved on 2007-03-21.
81. ^ Aphelion is 103.4% of the distance to perihelion. Due to the inverse square law, the radiation at perihelion is about 106.9% the energy at aphelion.
82. ^ Williams, Jack (December 20, 2005). Earth's tilt creates seasons. USAToday. Retrieved on 2007-03-17.
83. ^ Vázquez, M.; Montañés Rodríguez, P.; Palle, E. (2006). The Earth as an Object of Astrophysical Interest in the Search for Extrasolar Planets. Instituto de Astrofísica de Canarias. Retrieved on 2007-03-21.
84. ^ For the Earth, the Hill radius is
$begin{smallmatrix} R_H = aleft ( frac{m}{3M} right )^{frac{1}{3}} end{smallmatrix}$,
where m is the mass of the Earth, a is an Astronomical Unit, and M is the mass of the Sun. So the radius in A.U. is about: $begin{smallmatrix} left ( frac{1}{3 cdot 332,946} right )^{frac{1}{3}} = 0.01 end{smallmatrix}$.
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## References

• Yoder, Charles F. (1995). in T. J. Ahrens: Global Earth Physics: A Handbook of Physical Constants. Washington: American Geophysical Union. ISBN 0875908519. Retrieved on 2007-03-17.
• Williams, David R. (September 1, 2004). Earth Fact Sheet. NASA. Retrieved on 2007-03-17.
• Comins, Neil F. (2001). Discovering the Essential Universe, Second Edition, W. H. Freeman. ISBN 0-7167-5804-0. Retrieved on 2007-03-17.
• Kirk Munsell:Solar System Exploration: Earth. NASA (October 19, 2006). Retrieved on 2007-03-17.

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 76th day of the year (77th in leap years) in the Gregorian calendar. ... is the 244th day of the year (245th in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 76th day of the year (77th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 76th day of the year (77th in leap years) in the Gregorian calendar. ... is the 292nd day of the year (293rd in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 76th day of the year (77th in leap years) in the Gregorian calendar. ...

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