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                        Earth
                        Fro m Wikipedia, the free encyclo pedia

                           This article is about the planet. For other uses, see Earth (disambiguation).
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                        Eart h is the third planet from the Sun, and the densest and fifth- largest of the eight                                 Earth
Main page
                        planets in the Solar System. It is also the largest of the Solar System's four terrestrial
Co ntents               planets. It is sometimes referred to as the world, the Blue Planet, [21] or by its Latin name,
Featured co ntent
                        Terra.[note 6]
Current events
                        Earth formed approximately 4.54 billion years ago by accretion from the solar nebula ,
Rando m article
                        and life appeared on its surface within one billion years.[22] The planet is home to
Do nate to Wikipedia
                        millions of species, including humans.[23] Earth's biosphere has significantly altered the
                        atmosphere and other abiotic conditions on the planet, enabling the proliferation of
Interactio n
                        aerobic organisms as well as the formation of the oz one layer, which together with
Help                    Earth's magnetic field blocks harmful solar radiation, thus permitting formerly ocean-
Abo ut Wikipedia        confined life to move safely to land.[24] The physical properties of the Earth, as well as
Co mmunity po rtal      its geological history and orbit, have allowed life to persist. Estimates on how much
Recent changes          longer the planet will to be able to continue to support life range from 500 million years,
Co ntact Wikipedia      to as long as 2.3 billion years.[25][26][27]
                        Earth's crust is divided into several rigid segments, or tectonic plates, that migrate
To o lbo x              across the surface over periods of many millions of years . About 71% of the surface is
                                                                                                                                " The Blue Marble" photograph of Earth,
                        covered by salt water oceans, with the remainder consisting of continents and islands                             taken from Apollo 17
What links here
                        which together have many lakes and other sources of water that contribute to the
Related changes                                                                                                                                  D e sig nat io ns
                        hydrosphere. Earth's poles are mostly covered with ice that is the solid ice of the
Uplo ad file                                                                                                              Alt e rnat ive         Terra, Gaia
                        Antarctic ice sheet and the sea ice that is the Polar ice packs . The planet's interior           name s
Special pages
                        remains active, with a thick layer of relatively solid mantle, a liquid outer core that
Permanent link                                                                                                                             O rb it al charact e rist ics
                        generates a magnetic field, and a solid iron inner core .
Cite this page                                                                                                                               Epoch J2000.0 [n o te 1 ]
                        Earth interacts with other objects in space, especially the Sun and the Moon. During one
                                                                                                                          Ap he lio n            152,098,232 km
                        orbit around the sun, the Earth rotates about its own axis 366.26 times, creating 365.26                                 1.01671388 AU[n o te 2 ]
Print/expo rt
                        solar days , or one sidereal year.[note 7] The Earth's axis of rotation is tilted 23.4° away
                                                                                                                          Pe rihe lio n          147,098,290 km
Create a bo o k         from the perpendicular of its orbital plane, producing seasonal variations on the planet's                               0.98329134 AU[n o te 2 ]
                                                                                                                                                                        PDFmyURL.com
                                                                                                                                            0.98329134 AU
Do wnlo ad as PDF    surface with a period of one tropical year (365.24 solar days). [28] The Moon is Earth's
                                                                                                                      Se mi- majo r         149,598,261 km
Printable versio n   only natural satellite. It began orbiting the Earth about 4.53 billion years ago. The Moon's     axis                  1.00000261 AU[1 ]
                     gravitational interaction with Earth stimulates ocean tides, stabiliz es the axial tilt, and
                                                                                                                      Ecce nt ricit y       0.01671123[1 ]
Languages            gradually slows the planet's rotation.
                                                                                                                      O rb it al p e rio d 365.256363004 days [2 ]
                     Both the mineral resources of the planet and the products of the biosphere contribute                                 1.000017421 yr
Acèh
                     resources that are used to support a global human population.[29] These inhabitants are          Ave rag e             29.78 km/s [3]
Afrikaans
                     grouped into about 200 independent sovereign states, which interact through diplomacy,           o rb it al sp e e d   107,200 km/h
Alemannisch
                     travel, trade, and military action. Human cultures have developed many views of the              Me an ano maly 357.51716° [3]
አማርኛ
                     planet, including its personification as a planetary deity, its shape as flat, its position as
Ænglisc                                                                                                               Inclinat io n         7.155° to Sun's equator
                     the center of the universe , and in the modern Gaia Principle, as a single, self- regulating                           1.57869° [4 ] to invariable plane
Аҧсшəа
                     organism in its own right.
‫اﻟﻌرﺑﯾ ﺔ‬                                                                                                              Lo ng it ud e o f     348.73936° [3][n o te 3]
Arago nés                                                                                                             asce nd ing
                                        Co nt e nt s                                                                  no d e
                      1 Name and etymo lo gy
Arpetan                                                                                                               Arg ume nt o f        114.20783° [3][n o te 4 ]
                      2 Chro no lo gy                                                                                 p e rihe lio n
অসমীয়া
                          2.1 Fo rmatio n                                                                             Sat e llit e s
Asturianu                                                                                                                                   1 natural (the Moon)
                          2.2 Evo lutio n o f life
Avañe'ẽ
                          2.3 Future
Aymar aru                                                                                                                                   8,300+ artificial (as of 1 March
                      3 Co mpo sitio n and structure
Azərbaycanca                                                                                                                                2001) [5 ]
                          3.1 Shape
বাংলা                                                                                                                                  Physical charact e rist ics
                          3.2 Chemical co mpo sitio n
Bân-lâm-gú                                                                                                            Me an rad ius         6,371.0 km[6 ]
                          3.3 Internal structure
Basa Banyumasan                                                                                                       Eq uat o rial         6,378.1 km[7][8 ]
                          3.4 Heat
Беларуская                                                                                                            rad ius
                          3.5 Tecto nic plates
Беларуская                                                                                                            Po lar rad ius        6,356.8 km[9 ]
(тарашкевіца)             3.6 Surface
                          3.7 Hydro sphere                                                                            Flat t e ning         0.0033528 [1 0 ]
भोजपुरी
Biko l Central            3.8 Atmo sphere                                                                             C ircumf e re nce 40,075.017 km (equatorial) [8 ]
                              3.8 .1 Weather and climate                                                                                    40,007.86 km (meridional) [11 ][1 2 ]
Български
                                 3.8 .2 Upper atmo sphere                                                             Surf ace are a
Bo arisch                                                                                                                                   510,072,000 km2 [1 3][1 4 ][n o te 5 ]
                          3.9 Magnetic field                                                                                                148,940,000 km2 land (29.2 % )
བོད་ཡིག
                      4 Orbit and ro tatio n
Bo sanski                                                                                                                                   361,132,000 km2 water (70.8 % )
                          4.1 Ro tatio n
Brezho neg                                                                                                            Vo lume               1.08321 ×10 1 2 km3[3]
                          4.2 Orbit
Català
                          4.3 Axial tilt and seaso ns                                                                 Mass                  5.9736 ×10 2 4 kg [3]
Чӑвашла
                      5 Mo o n                                                                                        Me an d e nsit y      5.515 g/cm3[3]
Cebuano
                      6 Habitability                                                                                  Eq uat o rial      9.780327 m/s 2 [1 5 ]
Česky
                          6 .1 Bio sphere                                                                             surf ace g ravit y 0.99732 g
                                                                                                                                                                        PDFmyURL.com
                           6 .1 Bio sphere                                                                            surf ace g ravit y 0.99732 g
Chavacano de
Zambo anga                 6 .2 Natural reso urces and land use                                                       Escap e             11.186 km/s [3]
Cymraeg                    6 .3 Natural and enviro nmental hazards                                                    ve lo cit y

Dansk                      6 .4 Human geo graphy                                                                      Sid e re al         0.99726968 d [1 6 ]
Deutsch                7 Cultural viewpo int                                                                          ro t at io n        23h 56 m 4.100 s
                       8 See also                                                                                     p e rio d

Diné bizaad            9 No tes                                                                                       Eq uat o rial       1,674.4 km/h (465.1 m/s) [1 7]
                                                                                                                      ro t at io n
Do lno serbski         10 References
                                                                                                                      ve lo cit y
Eesti                  11 Further reading
                                                                                                                      Axial t ilt         23°26'21" .4119 [2 ]
Ελληνικά               12 External links
                                                                                                                      Alb e d o           0.367 (geometric) [3]
Emiliàn e rumagnò l
Эрзянь                Name and etymology                                                                                                  0.306 (Bond) [3]
Españo l                                                                                                              Surf ace t e mp . min          me an          max
Esperanto             The modern English noun earth developed from Middle English erthe (recorded in 1137),            K e lvin         184 K [1 8 ] 287.2 K [1 9 ] 331 K [2 0 ]
                      itself from Old English eorthe (dating from before 725), ultimately deriving from Proto-                          −89.2 °C 14 °C              57.8 °C
Estremeñu                                                                                                              C e lsius
Euskara               Germanic *erthō. Earth has cognates in all other Germanic languages, including Dutch                                 At mo sp he re
‫ﻓﺎرﺳﯽ‬                 aarde, German Erde, and Swedish, Norwegian, and Danish jord.[30] The Earth is                   Surf ace            101.325 kPa (MSL)
Fiji Hindi            personified as a goddess in Germanic paganism (appearing as Jörð in Norse                       p re ssure
Føro yskt             mythology, mother of the god Thor).[31]                                                         C o mp o sit io n   78.08% nitrogen (N2 ) [3] (dry air)
Français              In general English usage, the name earth can be capitaliz ed or spelled in lowercase                                20.95% oxygen (O 2 )
Frysk                                                                                                                                     0.93% argon
                      interchangeably, either when used absolutely or prefixed with "the" (i.e. "Earth", "the
                                                                                                                                          0.038% carbon dioxide
Furlan                Earth", "earth", or "the earth"). Many deliberately spell the name of the planet with a
                                                                                                                                          About 1% water vapor (varies
Gaeilge               capital, both as "Earth" or "the Earth". This is to distinguish it as a proper noun, distinct                       with climate)
Gaelg                 from the senses of the term as a count noun or verb (e.g. referring to soil, the ground,
Gàidhlig              earthing in the electrical sense, etc.). Oxford spelling recogniz es the lowercase form as the most common, with the capitaliz ed form as a
Galego                variant of it. Another convention that is very common is to spell the name with a capital when occurring absolutely (e.g. Earth's
贛語                    atmosphere) and lowercase when preceded by "the" (e.g. the atmosphere of the earth). The term almost exclusively exists in lowercase
ગુજ રાતી              when appearing in common phrases, even without "the" preceding it (e.g. "It does not cost the earth.", "What on earth are you doing?
Hak-kâ-fa             ").[32]
Хальмг
한국어                   Chronology
Hausa
Hawai`i               Formation
Հայերեն
                         Main article: History of the Earth
िह दी
Ho rnjo serbsce       The earliest material found in the Solar System is dated to 4.5666- 4.5678 bya (billion years ago);[33] therefore, it is inferred that the Earth,
Hrvatski              must have formed around this time. By 4.50- 4.58 bya [22] the primordial Earth had formed. The formation and evolution of the Solar

                                                                                                                                                                    PDFmyURL.com
Ido                 System bodies occurred in tandem with the Sun. In theory a solar nebula partitions a volume out of a molecular cloud by gravitational
Igbo                collapse, which begins to spin and flatten into a circumstellar disk , and then the planets grow out of that in tandem with the star. A nebula
Ilo kano            contains gas, ice grains and dust (including primordial nuclides). In nebular theory planetesimals commence forming as particulate
Bahasa Indo nesia   accrues by cohesive clumping and then by gravity. The assembly of the primordial Earth proceeded for 10– 20 myr (million years).[34]
Interlingua         The Moon formed shortly thereafter, 4.53 bya.[35]
ᐃᓄᒃᑎᑐᑦ/inuktitut    The Moon's formation remains a mystery. The working hypothesis is that it formed by accretion from material loosed from the Earth after a
Иро н               Mars- siz ed object, dubbed Theia, had a giant impact with Earth, [36] but the model is not self- consistent. In this scenario the mass of
Íslenska            Theia is 10% of the Earth's mass, [37] it impacts with the Earth in a glancing blow, [38] and some of its mass merges with the Earth. Between
Italiano            approximately 3.8 and 4.1 bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the
‫ע ברית‬              greater surface environment of the Moon, and by inference, to the Earth.
Basa Jawa
                    Earth's atmosphere and oceans formed by volcanic activity and outgassing that included water vapor . The origin of the world's oceans
Kalaallisut
                    was condensation augmented by water and ice delivered by asteroids, proto- planets, and comets.[39] In this model, atmospheric
ಕನಡ
                    "greenhouse gases" kept the oceans from freez ing while the newly forming Sun was only at 70% luminosity.[40] By 3.5 bya, the Earth's
Kapampangan
                    magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind .[41]
Къарачай-малкъар
ქართული             A crust formed when the molten outer layer of the planet Earth cooled to form a solid as the accumulated water vapor began to act in the
Kaszëbsczi          atmosphere. The two models [42] that explain land mass propose either a steady growth to the present- day forms [43] or, more likely, a
Қазақша             rapid growth[44] early in Earth history [45] followed by a long- term steady continental area.[46][47][48] Continents formed by plate tectonics,
Kerno wek           a process ultimately driven by the continuous loss of heat from the earth's interior. On time scales lasting hundreds of millions of years,
Kinyarwanda         the supercontinents have formed and broken up three times. Roughly 750 mya (million years ago), one of the earliest known
Kiswahili           supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 mya, then finally Pangaea,
Ко ми               which also broke apart 180 mya.[49]
Ko ngo
Kreyò l ayisyen
                    Evolution of life
Kurdî                  Main article: Evolutionary history of life
Кыргызча               For more details on the current eon, see Geological history of Earth .
Ladino
                    Highly energetic chemistry is believed to have produced a self- replicating molecule around 4 bya ( billion years ago) and half a billion
Лезги
                    years later the last common ancestor of all life existed.[50] The development of photosynthesis allowed the Sun's energy to be harvested
ລາວ
                    directly by life forms; the resultant oxygen accumulated in the atmosphere and formed a layer of oz one (a form of molecular oxygen [O 3])
Latgaļ u
                    in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called
Latina
                    eukaryotes.[51] True multicellular organisms formed as cells within colonies became increasingly specializ ed. Aided by the absorption of
Latviešu
                    harmful ultraviolet radiation by the oz one layer, life coloniz ed the surface of Earth. [52]
Lëtzebuergesch
Lietuvių            Since the 1960s, it has been hypothesiz ed that severe glacial action between 750 and 580 mya (million years ago), during the
Ligure              Neoproteroz oic, covered much of the planet in a sheet of ice. This hypothesis has been termed " Snowball Earth", and is of particular
Limburgs            interest because it preceded the Cambrian explosion, when multicellular life forms began to proliferate. [53]


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Lingála             Following the Cambrian explosion, about 535 mya, there have been five major mass extinctions .[54] The most recent such event was
Lo jban             65 mya, when an asteroid impact triggered the extinction of the (non- avian) dinosaurs and other large reptiles, but spared some small
Lumbaart            animals such as mammals, which then resembled shrews. Over the past 65 million years, mammalian life has diversified, and several
Magyar              million years ago an African ape- like animal such as Orrorin tugenensis gained the ability to stand upright.[55] This enabled tool use and
Македо нски         encouraged communication that provided the nutrition and stimulation needed for a larger brain, which allowed the evolution of the human
Malagasy            race. The development of agriculture, and then civiliz ation, allowed humans to influence the Earth in a short time span as no other life
മലയാളം              form had, [56] affecting both the nature and quantity of other life forms.
Malti
                    The present pattern of ice ages began about 40 mya and then intensified during the Pleistocene about 3 mya. High- latitude regions have
मराठी
                    since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 yr. The last continental glaciation ended
მარგალური
                    10,000 years ago.[57]
‫ﻣﺻر ى‬
‫ﻣﺎزروﻧﯽ‬
    ِ               Future
Bahasa Melayu
                       Main article: Future of the Earth
       ̤
Mìng-dĕ ng-ngṳ
             ̄
Mirandés               See also: Risks to civilization, humans and planet Earth
Мо кшень
Мо нго л
မြန်မာဘာသာ
Nāhuatl
Nederlands
Nedersaksisch
नेपाली
नेपाल भाषा
日本語
Nnapulitano
                               The life cycle of the Sun
No rdfriisk
No rfuk / Pitkern   The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium at the Sun's core, the star's total
No rsk (bo kmål)    luminosity will slowly increase. The luminosity of the Sun will grow by 10% over the next 1.1 byr (billion years) and by 40% over the next
No rsk (nyno rsk)   3.5 byr.[58] Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the loss of
No uo rmand         the planet's oceans.[59]
No vial
                    The Earth's increasing surface temperature will accelerate the inorganic CO 2 cycle, reducing its concentration to levels lethally low for
Occitan
                    plants (10 ppm for C4 photosynthesis) in approximately 500- 900 myr.[25] The lack of vegetation will result in the loss of oxygen in the
Олык марий
                    atmosphere, so animal life will become extinct within several million more years.[60] After another billion years all surface water will have
ଓଡ଼ିଆ
                    disappeared [26] and the mean global temperature will reach 70 °C[60] (158 °F). The Earth is expected to be effectively habitable for
Oʻzbekcha
                    about another 500 myr from that point, [25] although this may be extended up to 2.3 byr (billion years) if the nitrogen is removed from the
ਪੰਜ ਾਬੀ
                    atmosphere.[27] Even if the Sun were eternal and stable, 27% of the water in the modern oceans will descend to the mantle in one billion
Pälzisch
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Pälzisch
                     years due to reduced steam venting from mid- ocean ridges.[61]
‫ﭘﻧﺟﺎﺑﯽ‬
Papiamentu           The Sun, as part of its evolution, will become a red giant in about 5 byr. Models predict that the Sun will expand out to about 250 times
‫ﭘ ﺗو‬                 its present radius, roughly 1 AU (150,000,000 km).[58][62] Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its
Перем Ко ми          mass, so, without tidal effects, the Earth will move to an orbit 1.7 AU (250,000,000 km) from the Sun when the star reaches it maximum
                     radius. The planet was therefore initially expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though
                     most, if not all, remaining life would have been destroyed by the Sun's increased luminosity (peaking at about 5000 times its present
Piemo ntèis          level).[58] A 2008 simulation indicates that Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's
To k Pisin           atmosphere and be vaporiz ed.[62] After that, the Sun's core will collapse into a white dwarf, as its outer layers are ejected into space as
Plattdüütsch         a planetary nebula. The matter that once made up the Earth will be released into interstellar space, where it will one day become
Po lski              incorporated into a new generation of planets and other celestial bodies.
Po rtuguês
Qırımtatarca         Composition and structure
Ripo arisch
Ro mână                 Main article: Earth science
Ro mani                 Further information: Earth physical characteristics tables
Rumantsch
                     Earth is a terrestrial planet, meaning that it is a rocky body, rather than a gas giant like Jupiter. It
Runa Simi
                     is the largest of the four solar terrestrial planets in siz e and mass. Of these four planets, Earth
Русиньскый
                     also has the highest density, the highest surface gravity, the strongest magnetic field, and fastest
Русский
                     rotation, [63] and is probably the only one with active plate tectonics.[64]                               Siz e comparison of inner planets
Саха тыла                                                                                                                       (left to right): Mercury, Venus, Earth and
Sámegiella           Shape                                                                                                      Mars in true- color.
सं कतम्
    ृ
                        Main article: Figure of the Earth
Sardu
Sco ts               The shape of the Earth approximates an oblate spheroid, a sphere flattened along the axis from
Seso tho             pole to pole such that there is a bulge around the equator.[66] This bulge results from the rotation
Seso tho sa Lebo a   of the Earth, and causes the diameter at the equator to be 43 km (kilometer) larger than the
Shqip                pole- to- pole diameter.[67] For this reason the furthest point on the surface from the Earth's center
Sicilianu            of mass is the Chimboraz o volcano in Ecuador.[68] The average diameter of the reference
  ංහල                spheroid is about 12,742 km, which is approximately 40,000 km/π, as the meter was originally
Simple English       defined as 1/10,000,000 of the distance from the equator to the North Pole through Paris,
Slo venčina          France.[69]
Slo venščina         Local topography deviates from this idealiz ed spheroid, although on a global scale, these         Chimboraz o, Ecuador . The
Сло вѣ́н ьскъ /      deviations are small: Earth has a tolerance of about one part in about 584, or 0.17%, from the     furthermost point on the Earth's surface

                     reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls.[70] The      from its center.[6 5 ]
Ślůnski
                     largest local deviations in the rocky surface of the Earth are Mount Everest (8848 m above local
So o maaliga
                     sea level) and the Mariana Trench (10,911 m below local sea level). Because of the equatorial bulge, the surface locations farthest from
‫ﮐورد ی‬
                                                                                                                                                              PDFmyURL.com
‫ﮐورد ی‬
                       the center of the Earth are the summits of Mount Chimboraz o in Ecuador and Huascarán in Peru.[71][72][73]
Српски / srpski
Srpsko hrvatski /      Chemical composition
српско хрватски
                                                                                                                         Chemical composit ion of t he crust [74]
Basa Sunda                See also: Abundance of elements on Earth                                                                                       Composit ion
                                                                                                                       Compound            Formula
Suo mi                 The mass of the Earth is approximately 5.98 × 10 24 kg. It is composed mostly                                                  C o nt ine nt al O ce anic
Svenska                of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur              silica                      SiO 2           60.2%       48.6%
Tagalo g               (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with the remaining
                                                                                                                alumina                     Al2 O 3          15.2%      16.5%
த                      1.2% consisting of trace amounts of other elements. Due to mass segregation,
Татарча/tatarça        the core region is believed to be primarily composed of iron (88.8%), with               lime                        CaO               5.5%      12.3%
    లుగు               smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace                  magnesia                    MgO               3.1%       6.8%
ไทย                    elements.[75]                                                                            iron(II) oxide              FeO               3.8%       6.2%
То ҷ икӣ
                       The geochemist F. W. Clarke calculated that a little more than 47% of the                sodium oxide                Na 2 O            3.0%       2.6%
ᏣᎳᎩ
                       Earth's crust consists of oxygen. The more common rock constituents of the
Türkçe                                                                                                          potassium oxide             K2 O              2.8%       0.4%
                       Earth's crust are nearly all oxides; chlorine, sulfur and fluorine are the only
Українська                                                                                                      iron(III) oxide            Fe 2 O 3           2.5%       2.3%
                       important exceptions to this and their total amount in any rock is usually much
‫اردو‬
                       less than 1%. The principal oxides are silica, alumina, iron oxides, lime,               water                       H2 O              1.4%        1.1%
 ‫ / ﺋۇﯾﻐۇرﭼ‬Uyghurche
                       magnesia, potash and soda. The silica functions principally as an acid,                  carbon dioxide              CO 2              1.2%       1.4%
Vahcuengh
                       forming silicates, and all the commonest minerals of igneous rocks are of this
Vèneto                                                                                                          titanium dioxide            TiO 2             0.7%       1.4%
                       nature. From a computation based on 1,672 analyses of all kinds of rocks,
Vepsän kel’                                                                                                     phosphorus pentoxide        P2 O 5            0.2%       0.3%
                       Clarke deduced that 99.22% were composed of 11 oxides (see the table at
Tiếng Việt
                       right), with the other constituents occurring in minute quantities.[76]                                    Tot al                    99.6%      99.9%
Vo lapük
Võ ro
                       Internal structure
Walo n
                          Main article: Structure of the Earth
文言
West-Vlams             The interior of the Earth, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological)
Winaray                properties, but unlike the other terrestrial planets, it has a distinct outer and inner core. The outer layer of the Earth is a chemically distinct
Wo lo f                silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić
吴语                     discontinuity, and the thickness of the crust varies: averaging 6 km (kilometers) under the oceans and 30- 50 km on the continents. The
‫יי ִדיש‬                crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, and it is of the lithosphere that the tectonic
Yo rùbá                plates are comprised. Beneath the lithosphere is the asthenosphere, a relatively low- viscosity layer on which the lithosphere rides.
粵語                     Important changes in crystal structure within the mantle occur at 410 and 660 km below the surface, spanning a transition z one that
Zazaki                 separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core .[77]
Zeêuws                 The inner core may rotate at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year. [78]
Žemaitėška                                                                    Geologic layers of t he Eart h[79]
中文

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中文
                                                                                                 Dept h[80]                           Densit y
                                                                                                       km          Component Layer      g /cm3

                                                                                                       0–60   Lithosphere [note 8]        —
                                                                                                       0–35    Crust [note 9]          2.2–2.9
                                                                                                      35–60    Upper mantle            3.4–4.4
                                                                                                   35–2890    Mantle                   3.4–5.6
                                                                                                  100–700      Asthenosphere              —
                                                                                                 2890–5100    Outer core              9.9–12.2
                  Eart h cut away f ro m co re t o e xo sp he re . N o t t o scale .             5100–6378    Inner core              12.8–13.1

     Heat
     Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through
     radioactive decay (80%).[81] The major heat- producing isotopes in the Earth are potassium- 40, uranium- 238, uranium- 235, and thorium-
     232.[82] At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa.[83] Because much of
     the heat is provided by radioactive decay, scientists believe that early in Earth history, before isotopes with short half- lives had been
     depleted, Earth's heat production would have been much higher. This extra heat production, twice present- day at approximately 3 byr
     (billion years ago), [81] would have increased temperature gradients within the Earth, increasing the rates of mantle convection and plate
     tectonics, and allowing the production of igneous rocks such as komatiites that are not formed today. [84]

                     Present - day major heat - producing isot opes [85]
                                   Half - lif e
                Heat release                      Mean mant le concent rat ion Heat release
     Isot ope
                W/kg iso t o p e                       kg iso t o p e /kg mant le      W/kg mant le
                                     ye ars
       238 U    9.46 × 10 −5       4.47 × 10 9               30.8 × 10 −9              2.91 × 10 −12
       235 U     5.69 × 10 −4      7.04 × 10 8               0.22 × 10 −9              1.25 × 10 −13
      232 Th     2.64 × 10 −5 1.40 × 10 10                    124 × 10 −9              3.27 × 10 −12
        40 K     2.92 × 10 −5      1.25 × 10 9               36.9 × 10 −9              1.08 × 10 −12

     The mean heat loss from the Earth is 87 mW m −2 , for a global heat loss of 4.42 × 10 13 W.[86] 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.[87] More of the heat in the Earth is lost through plate tectonics, by mantle upwelling associated
     with mid- ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs in the
     oceans because the crust there is much thinner than that of the continents.[88]


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Tectonic plates
   Main article: Plate tectonics
                                                                                                       Eart h's main plat es [89]
The mechanically rigid outer layer of the Earth, the lithosphere, is broken into pieces called
tectonic plates. These plates are rigid segments that move in relation to one another at one
of three types of plate boundaries: Convergent boundaries , at which two plates come
together, Divergent boundaries , at which two plates are pulled apart, and Transform
boundaries, in which two plates slide past one another laterally. Earthquakes, volcanic
activity, mountain- building, and oceanic trench formation can occur along these plate
boundaries.[90] The tectonic plates ride on top of the asthenosphere, the solid but less-
viscous part of the upper mantle that can flow and move along with the plates, [91] and their
motion is strongly coupled with convection patterns inside the Earth's mantle.
As the tectonic plates migrate across the planet, the ocean floor is subducted under the                                            Area
leading edges of the plates at convergent boundaries. At the same time, the upwelling of                 Plat e name
                                                                                                                                10 6 km2
mantle material at divergent boundaries creates mid- ocean ridges. The combination of these
processes continually recycles the oceanic crust back into the mantle. Because of this             Pacific Plate                    103.3
recycling, most of the ocean floor is less than 100 myr (million years old) in age. The oldest     African Plate [note 10]          78.0
oceanic crust is located in the Western Pacific, and has an estimated age of about
200 myr.[92][93] By comparison, the oldest dated continental crust is 4,030 myr.[94]               North American Plate             75.9

The seven major plates are the Pacific, North American, Eurasian, African, Antarctic, Indo-        Eurasian Plate                   67.8
Australian, and South American. Other notable plates include the Arabian Plate, the                Antarctic Plate                  60.9
Caribbean Plate, the Naz ca Plate off the west coast of South America and the Scotia Plate in
the southern Atlantic Ocean. The Australian Plate fused with the Indian Plate between 50 and       Indo- Australian Plate           47.2
55 million years ago. The fastest- moving plates are the oceanic plates, with the Cocos Plate      South American Plate             43.6
advancing at a rate of 75 mm/year [95] and the Pacific Plate moving 52–69 mm/year. At the
other extreme, the slowest- moving plate is the Eurasian Plate, progressing at a typical rate
of about 21 mm/year.[96]

Surface
   Main articles: Landform and Extreme points of Earth
The Earth's terrain varies greatly from place to place. About 70.8% [97] of the surface is covered by water, with much of the continental
shelf below sea level. This equates to 148.94 million km 2 (57.51 million sq mi).[98] The submerged surface has mountainous features,
including a globe- spanning mid- ocean ridge system, as well as undersea volcanoes, [67] 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.
The planetary surface undergoes reshaping over geological time periods because of tectonics and erosion. The surface features built up
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The planetary surface undergoes reshaping over geological time periods because of tectonics and erosion. The surface features built up
or deformed through plate tectonics are subject to steady weathering from precipitation, thermal cycles, and chemical effects. Glaciation,
coastal erosion, the build- up of coral reefs, and large meteorite impacts [99] also act to reshape the landscape.
                                                       The continental crust consists of lower density material such as the igneous rocks
                                                       granite and andesite. Less common is basalt, a denser volcanic rock that is the
                                                       primary constituent of the ocean floors.[100] 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.[101] 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.[102] Common carbonate minerals include calcite (found
                                                       in limestone) and dolomite.[103]
                                                       The pedosphere is the outermost layer of the Earth that is composed of soil and
 Present- day Earth altimetry and bathymetry. Data
 from the National Geophysical Data Center 's          subject to soil formation processes. It exists at the interface of the lithosphere,
 TerrainBase Digital Terrain Model .                   atmosphere, hydrosphere and biosphere. Currently the total arable land is 13.31%
                                                       of the land surface, with only 4.71% supporting permanent crops.[14] Close to 40%
                                                       of the Earth's land surface is presently used for cropland and pasture, or an
estimated 1.3 × 10 7 km2 of cropland and 3.4 × 10 7 km2 of pastureland. [104]

The elevation of the land surface of the Earth varies from the low point of −418 m at the Dead Sea, to a 2005- estimated maximum
altitude of 8,848 m at the top of Mount Everest . The mean height of land above sea level is 840 m. [105]

Hydrosphere
   Main article: Hydrosphere
The abundance of water on Earth's surface is a unique feature that distinguishes




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The abundance of water on Earth's surface is a unique feature that distinguishes
the "Blue Planet" from others in the Solar System. The Earth's hydrosphere consists
chiefly of the oceans, but technically includes all water surfaces in the world,
including inland seas, lakes, rivers, and underground waters down to a depth of
2,000 m. The deepest underwater location is Challenger Deep of the Mariana
Trench in the Pacific Ocean with a depth of −10,911.4 m. [note 11][106]
The mass of the oceans is approximately 1.35 × 10 18 metric tons, or about 1/4400
of the total mass of the Earth. The oceans cover an area of 3.618 × 10 8 km2 with a
mean depth of 3,682 m, resulting in an estimated volume of 1.332 × 10 9 km3.[107] If
all the land on Earth were spread evenly, water would rise to an altitude of more
than 2.7 km.[note 12] About 97.5% of the water is saline, while the remaining 2.5% is
fresh water. Most fresh water, about 68.7%, is currently ice.[108]
The average salinity of the Earth's oceans is about 35 grams of salt per kilogram            Elevation histogram of the surface of the Earth
of sea water (35 ‰ ). [109] Most of this salt was released from volcanic activity or

extracted from cool, igneous rocks.[110] The oceans are also a reservoir of
dissolved atmospheric gases, which are essential for the survival of many aquatic life forms.[111] Sea water has an important influence on
the world's climate, with the oceans acting as a large heat reservoir .[112] Shifts in the oceanic temperature distribution can cause
significant weather shifts, such as the El Niño- Southern Oscillation.[113]

Atmosphere
   Main article: Atmosphere of Earth
The atmospheric pressure on the surface of the Earth averages 101.325 kPa, with a scale height of about 8.5 km. [3] It is 78% nitrogen
and 21% oxygen, with trace amounts of water vapor, carbon dioxide and other gaseous molecules. The height of the troposphere varies
with latitude, ranging between 8 km at the poles to 17 km at the equator, with some variation resulting from weather and seasonal
factors.[114]
Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 bya (billion years ago), forming the
primarily nitrogen- oxygen atmosphere of today. This change enabled the proliferation of aerobic organisms as well as the formation of
the oz one layer which blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life on Earth
include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating
temperature.[115] 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. Water vapor, carbon dioxide, methane and oz one are
the primary greenhouse gases in the Earth's atmosphere. Without this heat- retention effect, the average surface would be −18 °C, in
contrast to the current +15 °C, and life would likely not exist.[97]

Weather and climate
   Main articles: Weather and Climate
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The Earth's atmosphere has no definite boundary, slowly becoming thinner and fading into outer
space. Three- quarters of the atmosphere's mass is contained within the first 11 km of the
planet's surface. This lowest layer is called the troposphere. Energy from the Sun heats this
layer, and the surface below, causing expansion of the air. This lower density air then rises, and
is replaced by cooler, higher density air. The result is atmospheric circulation that drives the
weather and climate through redistribution of heat energy.[116]
The primary atmospheric circulation bands consist of the trade winds in the equatorial region            Satellite cloud cover image of Earth
below 30° latitude and the westerlies in the mid- latitudes between 30° and 60°.[117] Ocean              using NASA's Moderate- Resolution
                                                                                                         Imaging Spectroradiometer
currents are also important factors in determining climate, particularly the thermohaline circulation
that distributes heat energy from the equatorial oceans to the polar regions.[118]
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.[116] Most of the water is
then transported to lower elevations by river systems and usually returned to the oceans or deposited into lakes. This water cycle is a
vital mechanism for 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.[119]
The amount of solar energy reaching the Earth's decreases with increasing latitude. At higher latitudes the sunlight reaches the surface at
a lower angles and it must pass through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level
decreases by about 0.4 °C per per degree of latitude away from the equator.[120] 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.[121] Climate can also be classified based on the temperature and precipitation, with the climate
regions characteriz ed 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.[117]

Upper atmosphere
   See also: Outer space
Above the troposphere, the atmosphere is usually divided into the stratosphere, mesosphere,
and thermosphere.[115] Each layer has a different lapse rate, defining the rate of change in
temperature with height. Beyond these, the exosphere thins out into the magnetosphere, where
the Earth's magnetic fields interact with the solar wind .[122] Within the stratosphere is the oz one
layer, a component that partially shields the surface from ultraviolet light and thus is important for
life on Earth. The Kármán line, defined as 100 km above the Earth's surface, is a working
definition for the boundary between atmosphere and space.[123]
Thermal energy causes some of the molecules at the outer edge of the Earth's atmosphere                  This view from orbit shows the full

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Thermal energy causes some of the molecules at the outer edge of the Earth's atmosphere
                                                                                                          Moon partially obscured and deformed
have their velocity increased to the point where they can escape from the planet's gravity. This          by the Earth's atmosphere. NASA image
results in a slow but steady leakage of the atmosphere into space . Because unfixed hydrogen
has a low molecular weight, it can achieve escape velocity more readily and it leaks into outer
space at a greater rate than other gasses.[124] The leakage of hydrogen into space contributes to the pushing of the Earth from an
initially reducing state to its current oxidiz ing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such
as hydrogen is believed to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere.[125]
Hence the ability of hydrogen to escape from the Earth's atmosphere may have influenced the nature of life that developed on the
planet.[126] In the current, oxygen- rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead,
most of the hydrogen loss comes from the destruction of methane in the upper atmosphere. [127]

Magnetic field
   Main article: Earth's magnetic field
The Earth's magnetic field is shaped roughly as a magnetic dipole, with the poles
currently located proximate to the planet's geographic poles. At the equator of the
magnetic field, the magnetic field strength at the planet's surface is 3.05 × 10 −5 T,
with global magnetic dipole moment of 7.91 × 10 15 T m3.[128] According to dynamo
theory, the field is generated within the molten outer core region where heat creates
convection motions of conducting materials, generating electric currents. These in
turn produce the Earth's magnetic field. The convection movements in the core are
chaotic; the magnetic poles drift and 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.[129][130]
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               Schematic of Earth's magnetosphere. The solar
Earth. The collision between the magnetic field and the solar wind forms the Van           wind flows from left to right
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.[131]

Orbit and rotation

Rotation
   Main article: Earth's rotation
Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of
mean solar time (86,400.0025 SI seconds).[132] As the Earth's solar day is now slightly
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longer than it was during the 19th century because of tidal acceleration, each day
varies between 0 and 2 SI ms longer.[133][134]
Earth's rotation period relative to the fixed stars, called its stellar day by the
International Earth Rotation and Reference Systems Service (IERS), is
86164.098903691 seconds of mean solar time (UT1), or
23 h 56 m 4.098903691s .[2][note 13] Earth's rotation period relative to the precessing or
moving mean vernal equinox, misnamed its sidereal day , is
86164.09053083288 seconds of mean solar time (UT1)
(23 h 56 m 4.09053083288 s ).[2] Thus the sidereal day is shorter than the stellar day by
about 8.4 ms.[135] The length of the mean solar day in SI seconds is available from
the IERS for the periods 1623–2005[136] and 1962–2005.[137]                                    Earth's axial tilt (or obliquity) and its relation to
                                                                                               the rotation axis and plane of orbit
Apart from meteors within the atmosphere and low- orbiting satellites, the main
apparent motion of celestial bodies in the Earth's sky is to the west at a rate of 15°/h =
15'/min. For bodies near the celestial equator, this is equivalent to an apparent diameter of the Sun or Moon every two minutes; from the
planet's surface, the apparent siz es of the Sun and the Moon are approximately the same.[138][139]

Orbit
   Main article: Earth's orbit
Earth orbits the Sun at an average distance of about 150 million kilometers every 365.2564 mean solar days, or one sidereal year. From
Earth, this gives an apparent movement of the Sun eastward with respect to the stars at a rate of about 1°/day, or a Sun or Moon
diameter, every 12 hours. Because of this motion, on average it takes 24 hours—a solar day —for Earth to complete a full rotation about
its axis so that the Sun returns to the meridian. The orbital speed of the Earth averages about 29.8 km/s (107,000 km/h), which is fast
enough to cover the planet's diameter (about 12,600 km) in seven minutes, and the distance to the Moon (384,000 km) in four hours.[3]
The Moon revolves with the Earth around a common barycenter every 27.32 days relative to the background stars. When combined with
the Earth–Moon system's common revolution around the Sun, the period of the synodic month, from new moon to new moon, is
29.53 days. Viewed from the celestial north pole, the motion of Earth, the Moon and their axial rotations are all counter- clockwise. Viewed
from a vantage point above the north poles of both the Sun and the Earth, the Earth appears to revolve in a counterclockwise direction
about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.4 degrees from the perpendicular to
the Earth–Sun plane, and the Earth–Moon plane is tilted about 5 degrees against the Earth- Sun plane. Without this tilt, there would be an
eclipse every two weeks, alternating between lunar eclipses and solar eclipses .[3][140]
The Hill sphere, or gravitational sphere of influence, of the Earth is about 1.5 Gm (or 1,500,000 kilometers) in radius. [141][note 14] 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.
Earth, along with the Solar System, is situated in the Milky Way galaxy, orbiting about


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Earth, along with the Solar System, is situated in the Milky Way galaxy, orbiting about
28,000 light years from the center of the galaxy. It is currently about 20 light years above the
galaxy's equatorial plane in the Orion spiral arm.[142]

Axial tilt and seasons
   Main article: Axial tilt
Because of the axial tilt of the Earth, the amount of sunlight reaching any given point on the
surface varies over the course of the year. This results in seasonal change in climate, with
summer in the northern hemisphere occurring when the North Pole is pointing toward the Sun, and
winter taking place when the pole is pointed away. During the summer, the day lasts longer and
the Sun climbs higher in the sky. In winter, the climate becomes generally cooler and the days
shorter. Above the Arctic Circle, an extreme case is reached where there is no daylight at all for
part of the year—a polar night . In the southern hemisphere the situation is exactly reversed, with       Illustration of the Milky Way Galaxy,
                                                                                                          showing the location of the Sun
the South Pole oriented opposite the direction of the North Pole.
                                           By astronomical convention, the four seasons are
                                           determined by the solstices—the point in the orbit of maximum axial tilt toward or away from the
                                           Sun—and the equinoxes, when the direction of the tilt and the direction to the Sun are
                                           perpendicular. In the northern hemisphere, Winter Solstice occurs on about December 21,
                                           Summer Solstice is near June 21, Spring Equinox is around March 20 and Autumnal Equinox is
                                           about September 23. In the Southern hemisphere, the situation is reversed, with the Summer and
                                           Winter Solstices exchanged and the Spring and Autumnal Equinox dates switched.[143]
                                           The angle of the Earth's tilt is relatively stable over long periods of time. The tilt does undergo
                                           nutation; a slight, irregular motion with a main period of 18.6 years. [144] 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
 Earth and Moon from Mars, imaged          the Sun and Moon on the Earth's equatorial bulge. From the perspective of the Earth, the poles
 by Mars Reconnaissance Orbiter . From
                                           also migrate a few meters across the surface. This polar motion has multiple, cyclical
 space, the Earth can be seen to go
 through phases similar to the phases of   components, which collectively are termed quasiperiodic motion. In addition to an annual
 the Moon.                                 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.[145]
In modern times, Earth's perihelion occurs around January 3, and the aphelion around July 4. These dates change over time due to
precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. The changing Earth- Sun distance results
in an increase of about 6.9% [note 15] 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. This effect is much less significant than the total
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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.[146]

Moon
   Main article: Moon
                                                                                                                       Charact erist ics
The Moon is a relatively large, terrestrial, planet- like satellite, with a diameter about one- quarter of
                                                                                                              Diamet er           3,474.8 km
the Earth's. It is the largest moon in the Solar System relative to the siz e of its planet, although
Charon is larger relative to the dwarf planet Pluto. The natural satellites orbiting other planets are        Mass                7.349 × 10 22 kg
called "moons" after Earth's Moon.                                                                            Semi- major axis 384,400 km
The gravitational attraction between the Earth and Moon causes tides on Earth. The same effect on           Orbit al period       27 d 7 h 43.7 m
the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit the
Earth. As a result, it always presents the same face to the planet. As the Moon orbits Earth, different parts of its face are illuminated by the
Sun, leading to the lunar phases ; the dark part of the face is separated from the light part by the solar terminator .
Because of their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm a year. Over millions of years, these
tiny modifications—and the lengthening of Earth's day by about 23 µs a year—add up to significant changes. [147] 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.[148]
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 stabiliz ed by tidal interactions with the Moon.[149] Some theorists
believe that without this stabiliz ation against the torques applied by the Sun and
planets to the Earth's equatorial bulge, the rotational axis might be chaotically
unstable, exhibiting chaotic changes over millions of years, as appears to be the
case for Mars.[150]
Viewed from Earth, the Moon is just far enough away to have very nearly the same
apparent- siz ed disk as the Sun. The angular siz e (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.[139] This allows total and annular          Details of the Earth- Moon system. Besides the
solar eclipses to occur on Earth.                                                             radius of each object, the radius to the Earth- Moon
                                                                                              barycenter is shown. Photos from NASA . Data from
The most widely accepted theory of the Moon's origin, the giant impact theory ,               NASA . The Moon's axis is located by Cassini's third
states that it formed from the collision of a Mars- siz e protoplanet called Theia with       law.
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.[151]
Earth has at least five co- orbital asteroids, including 3753 Cruithne and 2002 AA 29 .[152][153] As of 2011, there are 931 operational, man-
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Earth has at least five                     , including                 and 2002 AA 29 .        As of 2011, there are 931 operational, man-
made satellites orbiting the Earth.[154] On July 27, 2011, astronomers reported a trojan asteroid companion, 2010 TK 7 , librating around
the leading Lagrange triangular point , L4, of Earth in Earth's orbit around the Sun.[155][156]




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


Habitability
   See also: Planetary habitability
A planet that can sustain life is termed habitable, even if life did not originate there. The Earth provides liquid water—an environment
where complex organic molecules can assemble and interact, and sufficient energy to sustain metabolism.[157] 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 current climatic conditions at the surface.[158]

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 bya (billion years ago). The biosphere is divided into a number of biomes, inhabited by broadly similar plants and animals. On land,
biomes are separated primarily by differences in latitude, height above sea level and humidity. Terrestrial biomes lying within the Arctic or
Antarctic Circles, at high altitudes or in extremely arid areas are relatively barren of plant and animal life; species diversity reaches a
peak in humid lowlands at equatorial latitudes .[159]

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.
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. [160] These bodies form
concentrated sources for many metals and other useful elements.
The Earth's biosphere produces many useful biological products for humans, including (but far from limited to) food, wood,
pharmaceuticals, oxygen, and the recycling of many organic wastes. The land- based ecosystem depends upon topsoil and fresh water,
and the oceanic ecosystem depends upon dissolved nutrients washed down from the land.[161] Humans also live on the land by using
building materials to construct shelters. In 1993, human use of land is approximately:

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 Land use      Arable land Permanent crops Permanent pastures Forests and woodland Urban areas Other
Percent age 13.13% [14]             4.71% [14]                  26%                      32%           1.5% 30%

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

Natural and environmental hazards
Large areas of the Earth's surface are subject to extreme weather such as tropical cyclones, hurricanes, or typhoons that dominate life in
those areas. From 1980–2000, these events caused an average of 11,800 deaths per year.[162] Many places are subject to
earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, bliz z ards, floods, droughts, wildfires, and other calamities
and disasters.
Many localiz ed areas are subject to human- made pollution of the air and water, acid rain and toxic substances, loss of vegetation
(overgraz ing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion, erosion, and introduction
of invasive species.
According to the United Nations, a scientific consensus exists linking human activities to global warming due to industrial carbon dioxide
emissions. This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges,
significant changes in weather and a global rise in average sea levels.[163]

Human geography
   Main article: Human geography
   See also: World
Cartography, the study and practice of map making, and vicariously geography, have historically been the disciplines devoted to
depicting the Earth. Surveying, the determination of locations and distances, and to a lesser extent navigation, the determination of
position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information.
Earth has reached approximately 7,000,000,000 human inhabitants as of October 31, 2011. [164] Projections indicate that the world's
human population will reach 9.2 billion in 2050.[165] 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.[166]
It is estimated that only one- eighth of the surface of the Earth is suitable for humans to live on—three- quarters is covered by oceans, and
half of the land area is either desert (14%), [167] high mountains (27%), [168] or other less suitable terrain. The northernmost permanent
settlement in the world is Alert, on Ellesmere Island in Nunavut, Canada.[169] (82°28′N) The southernmost is the Amundsen- Scott South
Pole Station, in Antarctica, almost exactly at the South Pole. (90°S)
Independent sovereign nations claim the planet's entire land surface, except for some parts of Antarctica and the odd unclaimed area of
Bir Tawil between Egypt and Sudan. As of 2011 there are 204 sovereign states, including the 193 United Nations member states . In
addition, there are 59 dependent territories , and a number of autonomous areas, territories under dispute and other entities. [14]
                                                                                                                                      PDFmyURL.com
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.[170]
The United Nations is a worldwide intergovernmental organiz ation that was created with the goal of intervening in the disputes between
nations, thereby avoiding armed conflict.[171] The U.N. serves primarily as a forum for international diplomacy and international law. When
the consensus of the membership permits, it provides a mechanism for armed intervention.[172]
The first human to orbit the Earth was Yuri Gagarin on April 12, 1961. [173] In total, about 487 people have visited outer space and
reached Earth orbit as of July 30, 2010, and, of these, twelve have walked on the Moon.[174][175][176] Normally the only humans in space
are those on the International Space Station. The station's crew, currently six people, is usually replaced every six months.[177] The
furthest humans have travelled from Earth is 400,171 km, achieved during the 1970 Apollo 13 mission.[178]




      The 7 continents of Earth: [1 79 ]              The Earth at night in 2000, a composite of
        North America ,     South America ,           DMSP/OLS ground illumination data on a
        Antarctica,    Africa,     Europe,    Asia,   simulated night- time image of the world. This
        Australia                                     image is not photographic and many features
                                                      are brighter than they would appear to a
                                                      direct observer.                                 ISS video beginning just south- east of
                                                                                                       Alaska. The first city that the ISS passes over
                                                                                                       (seen approximately 10 seconds into the
                                                                                                       video) is San Francisco and the surrounding
                                                                                                       areas. A careful examination shows where the
                                                                                                       Golden Gate Bridge is located: a smaller strip
                                                                                                       of lights just before the city of San Francisco,
                                                                                                       nearest to the clouds on the right of the
                                                                                                       image. Very obvious lightning storms can be
                                                                                                       seen on the Pacific Ocean coastline, with
                                                                                                       clouds overhead. As the video continues, the
                                                                                                       ISS passes over Central America (green
                                                                                                       lights can be seen here), with the Yucatan
                                                                                                       Peninsula on the left. The pass ends as the
                                                                                                       ISS is over the capital city of Bolivia, La Paz .


Cultural viewpoint
   Main article: Earth in culture

                                                                                                                                                  PDFmyURL.com
The standard astronomical symbol of the Earth consists of a cross circumscribed by a
circle.[180]
Unlike the rest of the planets in the Solar System, humankind did not begin to view the Earth as
a moving object in orbit around the Sun until the 16th century.[181] Earth has often been
personified as a deity, in particular a goddess. In many cultures a mother goddess is also
portrayed as a fertility deity. Creation myths in many religions recall a story involving the creation
of the Earth by a supernatural deity or deities. A variety of religious groups, often associated with
fundamentalist branches of Protestantism [182] or Islam, [183] assert that their interpretations of
these creation myths in sacred texts are literal truth and should be considered alongside or
replace conventional scientific accounts of the formation of the Earth and the origin and
development of life.[184] Such assertions are opposed by the scientific community [185][186] and
by other religious groups.[187][188][189] A prominent example is the creation- evolution
                                                                                                                      The first photograph ever taken by
controversy.
                                                                                                                      astronauts of an " Earthrise" , from Apollo
In the past there were varying levels of belief in a flat Earth, [190] but this was displaced by the                  8
concept of a spherical Earth due to observation and circumnavigation.[191] The human
perspective regarding the Earth has changed following the advent of spaceflight, and the
biosphere is now widely viewed from a globally integrated perspective.[192][193] This is reflected in a growing environmental movement
that is concerned about humankind's effects on the planet.[194]

See also
      Earth sciences portal                                                                                                        B o o k: Eart h
                                                                                                                                   B o o k: So lar Syst e m
                                                                                                                      Wi ki p e d i a b o o ks a r e co l l e cti o n s o f a r ti cl e s
                                                                                                                      th a t ca n b e d o wn l o a d e d o r o r d e r e d i n p r i n t.



Notes
   1. ^ All astro no mical quantities vary, bo th secularly and perio dically. The quantities given are the values at the instant J20 0 0 .0 o f the secular
      variatio n, igno ring all perio dic variatio ns.
   2. ^ a b aphelio n = a × (1 + e); perihelio n = a × (1 - e), where a is the semi-majo r axis and e is the eccentricity.
   3. ^ The reference lists the lo ngitude o f the ascending no de as −11.26 0 6 4°, which is equivalent to 348 .739 36 ° by the fact that any angle is equal
      to itself plus 36 0 °.
   4. ^ The reference lists the lo ngitude o f perihelio n , which is the sum o f the lo ngitude o f the ascending no de and the argument o f perihelio n. That
      is, 114.20 78 3° + (−11.26 0 6 4°) = 10 2.9 4719 °.
   5. ^ Due to natural fluctuatio ns, ambiguities surro unding ice shelves, and mapping co nventio ns fo r vertical datums, exact values fo r land and
      o cean co verage are no t meaningful. Based o n data fro m the Vecto r Map and Glo bal Landco ver datasets, extreme values fo r co verage o f

                                                                                                                                                                         PDFmyURL.com
     lakes and streams are 0 .6 % and 1.0 % o f the Earth's surface. The ice shields o f Antarctica and Greenland are co unted as land, even tho ugh
     much o f the ro ck which suppo rts them lies belo w sea level.
  6 . ^ By Internatio nal Astro no mical Unio n co nventio n, the term terra is used o nly fo r naming extensive land masses o n celestial bo dies o ther than
      the Earth. Cf. Blue, Jennifer (20 0 7-0 7-0 5). "Descripto r Terms (Feature Types)" . Gazetteer of Planetary Nomenclature . USGS. Retrieved
      20 0 7-0 7-0 5.
  7. ^ The number o f so lar days is o ne less than the number o f sidereal days because the o rbital mo tio n o f the Earth abo ut the Sun results in o ne
      additio nal revo lutio n o f the planet abo ut its axis.
  8 . ^ Lo cally varies between 5 and 20 0 km.
  9 . ^ Lo cally varies between 5 and 70 km.
 10 . ^ Including the So mali Plate, which is currently in the pro cess o f fo rmatio n o ut o f the African Plate. See: Cho ro wicz, Jean (Octo ber 20 0 5). "The
      East African rift system". Journal of African Earth Sciences 4 3 (1–3): 379 –410 . Bibco de 20 0 5JAfES..43..379 C .
      do i:10 .10 16 /j.jafrearsci.20 0 5.0 7.0 19 .
 11. ^ This is the measurement taken by the vessel Kaikō in March 19 9 5 and is believed to be the mo st accurate measurement to date. See the
     Challenger Deep article fo r mo re details.
 12. ^ The to tal surface area o f the Earth is 5.1 ×10 8 km 2 . To first appro ximatio n, the average depth wo uld be the ratio o f the two , o r 2.7 km.
 13. ^ Ao ki, the ultimate so urce o f these figures, uses the term "seco nds o f UT1" instead o f "seco nds o f mean so lar time".— Ao ki, S.; Kino shita, H.;
     Guino t, B.; Kaplan, G. H.; McCarthy, D. D.; Seidelmann, P. K. (19 8 2). "The new definitio n o f universal time". Astronomy and Astrophysics 10 5 (2):
     359 –36 1. Bibco de 19 8 2A&A...10 5..359 A .
 14. ^ Fo r the Earth, the Hill radius is
                          ,

     where m is the mass o f the Earth, a is an Astro no mical Unit, and M is the mass o f the Sun. So the radius in A.U. is abo ut:                             .

 15. ^ Aphelio n is 10 3.4% o f the distance to perihelio n. Due to the inverse square law, the radiatio n at perihelio n is abo ut 10 6 .9 % the energy at
     aphelio n.

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19 1. ^ Jaco bs, James Q. (19 9 8 -0 2-0 1). "Archaeo geo desy, a Key to Prehisto ry" . Retrieved 20 0 7-0 4-21.
19 2. ^ Fuller, R. Buckminster (19 6 3). Operating Manual fo r Spaceship Earth (First ed.). New Yo rk: E.P. Dutto n & Co . ISBN 0 -525-47433-1.
      http://www.futurehi.net/do cs/OperatingManual.html . Retrieved 20 0 7-0 4-21.
19 3. ^ Lo velo ck, James E. (19 79 ). Gaia: A New Look at Life on Earth (First ed.). Oxfo rd: Oxfo rd University Press. ISBN 0 -19 -28 6 0 30 -5.
19 4. ^ Fo r example: McMichael, Antho ny J. (19 9 3). Planetary Overload: Global Environmental Change and the Health of the Human Species .
      Cambridge University Press. ISBN 0 -521-45759 -9 .

Further reading
  Comins, Neil F. (2001). Discovering the Essential Universe (2nd ed.). W. H. Freeman. Bibcode 2003deu..book.....C . ISBN 0- 7167-
  5804- 0.

External links
  Earth - Profile     - Solar System Exploration         - NASA.                                                     Find more about Eart h on Wikipedia's
  Earth - Temperature and Precipitation Extremes             - NCDC.                                                            sister projects :
  Earth - Climate Changes Cause Shape to Change                 - NASA.                                                 Definitions and translations from
                                                                                                                        Wiktionary
  Earth - Geomagnetism Program             - USGS.
                                                                                                                        Images and media from Commons
  Earth - Astronaut Photography Gateway             - NASA.
  Earth - Observatory        - NASA.
                                                                                                                                                  PDFmyURL.com
 Earth - Observatory             - NASA.                                                                                        Learning resources from Wikiversity
 Earth - Audio (29:28) - Cain/Gay - Astronomy Cast (2007)                      .                                                News stories from Wikinews
 Earth - Videos - International Space Station:
                                                                                                                                Quotations from Wikiquote
      Video (01:02)           - Earth (Time- Lapse).
      Video (00:27)           - Earth and Auroras (Time- Lapse).                                                                Source texts from Wikisource

                                                                                                                                Textbooks from Wikibooks


V · T· E ·                                                                          T he So lar Syst e m




                    The Sun · Mercury · Venus · Eart h · Mars · Ceres · Jupiter · Saturn · Uranus · Neptune · Pluto · Haumea · Makemake · Eris ·
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                                                          Rings · Jovian · Saturnian · Uranian · Neptunian ·
                  Meteoroids · Minor planets · Asteroids · Asteroid belt · Centaurs · TNOs · Kuiper belt · Scattered disc · Comets · Oort cloud ·
                 Astronomical object · Star · Planet · Dwarf planet · Small Solar System body · Planetary system · List of Solar System objects ·
                                        List of Solar System objects by siz e · List of minor planets · Solar System Portal ·

V · T· E ·                                                                         Eart h-re lat e d t o pics
                         Age of the Earth · Evolutionary history of life · Faint young Sun paradox · Formation and evolution of the Solar System ·
             Hist o ry
                         Future of the Earth · Gaia hypothesis · Geologic time scale · Geological history of Earth · History of the Earth · Timeline of evolution ·
    G e o g rap hy       Clairaut's theorem · Continents · Earthquake · Equatorial bulge · Extremes on Earth · Geology of solar terrestrial planets ·
  and g e o lo g y       Plate tectonics · Structure of the Earth · Timez ones ·

        Eco lo g y       Earth Day · Gaia philosophy · Global warming · Human impact on the environment · Millennium Ecosystem Assessment ·

                         Bhuvan · Bing Maps · Google Earth · Google Maps · NASA World Wind · OpenStreetMap · Ovi Maps · Remote sensing ·
         Imag ing
                         Yahoo! Maps ·
  Art s, cult ure        Earth in culture · Earth in fiction · Etymology of the word " Earth" · Flat Earth and Hollow Earth · History of the world · International law ·
   and so cie t y        Landscape art · List of countries · World economy ·

    Sp irit ualit y      Creation myth · Creationism · Earth Mother · Gaia (Ancient Greece) · New Age Gaian · Planetary Logos (Theosophy) ·
and t e le o lo g y      Tellus Mater (Ancient Rome) ·

                                                             Earth sciences portal · Solar System portal ·

V · T· E ·                                                              Eart h's lo cat io n in t he unive rse
  Eart h      → Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion–Cygnus Arm → Milky Way → Milky Way subgroup →
                      Local Group → Virgo Supercluster → Pisces- Cetus Supercluster Complex → Observable universe → Universe
                                                          Each arrow should be read as " within" or " part of" .

V · T· E ·                                                                             Eart h scie nce
                                                                                                                                                           PDFmyURL.com
                                      Atmospheric science · Environmental science · Geodesy · Geology · Geophysics · Glaciology ·
                                                      Hydrology · Oceanography · Physical geography · Soil science ·
                                                                               Category · Portal ·

   V · T· E ·                                                                              T he Eart h
                  C o nt ine nt s   Africa · Antarctica · Asia · Australia · Europe · North America · South America ·

                         O ce ans   Arctic Ocean · Atlantic Ocean · Indian Ocean · Pacific Ocean · Southern Ocean ·
                                    Earth science · Future of the Earth · Geological history of Earth · Geology · History of the Earth · Plate tectonics ·
                           Eart h
                                    Structure of the Earth ·
   N at ural e nviro nme nt         Biome · Ecology · Ecosystem · Nature · Wilderness ·

        R e lat e d art icle s      Earth Day · Geology of solar terrestrial planets · Solar System · World ·

                                                                               Category · Portal ·

   V · T· E ·                                                                      Ele m e nt s o f nat ure
        Unive rse          Space · Time · Matter · Energy ·

                           Earth science · Future of the Earth · Geological history of Earth · Geology · History of the Earth · Plate tectonics ·
                Eart h
                           Structure of the Earth ·
         We at he r        Atmosphere of Earth · Climate · Meteorology ·

   Enviro nme nt           Ecology · Ecosystem · Wilderness ·
                           Biology · Eukaryota (Plants/Flora · Animals/Fauna · Fungi · Protista) · Evolutionary history of life · Hierarchy of life · Life on Earth ·
                 Lif e
                           Origin of life · Prokaryotes (Archaea · Bacteria) · Viruses ·
                                                                             C at e g o ry · Po rt al ·

                                                                                                                                List e n t o t his art icle (4 part s) ·
                                                                                                                                                 (inf o )
                                                                                                                                     Part 1 • Part 2 • Part 3 • Part 4

                                                                                                                                         Th i s a u d i o fi l e wa s cr e a te d fr o m a
                                                                                                                                         r e vi s i o n o f th e "Ea r th " a r ti cl e d a te d
                                                                                                                                         2 0 1 2 -0 6 -1 3, a n d d o e s n o t r e fl e ct
                                                                                                                                         s u b s e q u e n t e d i ts to th e a r ti cl e .
                                                                                                                                         ( Au d i o h e l p )
                                                                                                                                      Mo re spo ke n art icle s

 Categories: Earth Geography                   Geology      Terrestrial planets



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