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(Top)

1Etymology

2Natural history

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2.1Formation

2.2After formation

2.3Origin of life and evolution

2.4Future

3Physical characteristics

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3.1Size and shape

3.2Surface

3.3Tectonic plates

3.4Internal structure

3.5Chemical composition

3.6Internal heat

3.7Gravitational field

3.8Magnetic field

4Orbit and rotation

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4.1Rotation

4.2Orbit

4.3Axial tilt and seasons

5Earth–Moon system

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5.1Moon

5.2Asteroids and artificial satellites

6Hydrosphere

7Atmosphere

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7.1Weather and climate

7.2Upper atmosphere

8Life on Earth

9Human geography

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9.1Natural resources and land use

9.2Humans and the environment

10Cultural and historical viewpoint

11See also

12Notes

13References

14External links

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Earth

298 languages

AcèhАдыгэбзэАдыгабзэAfrikaansAlemannischአማርኛAnarâškielâअंगिकाÆngliscАԥсшәаالعربيةAragonésܐܪܡܝܐԱրեւմտահայերէնArmãneashtiArpetanঅসমীয়াAsturianuAtikamekwअवधीAvañe'ẽАварAymar aruAzərbaycancaتۆرکجهBasa BaliBamanankanবাংলাBanjarBân-lâm-gúBasa BanyumasanБашҡортсаБеларускаяБеларуская (тарашкевіца)भोजपुरीBikol CentralБългарскиBoarischབོད་ཡིགBosanskiBrezhonegБуряадCatalàЧӑвашлаCebuanoČeštinaChavacano de ZamboangaChi-ChewaChiShonaChiTumbukaCorsuCymraegDagbanliDanskالدارجةDavvisámegiellaDeitschDeutschދިވެހިބަސްDiné bizaadDolnoserbskiडोटेलीཇོང་ཁEestiΕλληνικάEmiliàn e rumagnòlЭрзяньEspañolEsperantoEstremeñuEuskaraفارسیFiji HindiFøroysktFrançaisFryskFurlanGaeilgeGaelgGàidhligGalegoГӀалгӀай贛語Gĩkũyũگیلکیગુજરાતીगोंयची कोंकणी / Gõychi KonknniGungbe客家語/Hak-kâ-ngîХальмг한국어HausaHawaiʻiՀայերենहिन्दीHornjoserbsceHrvatskiIdoIgboIlokanoBahasa IndonesiaInterlinguaInterlingueᐃᓄᒃᑎᑐᑦ / inuktitutIñupiatunИронIsiZuluÍslenskaItalianoעבריתJawaKabɩyɛKalaallisutಕನ್ನಡKapampanganКъарачай-малкъарქართულიकॉशुर / کٲشُرKaszëbscziҚазақшаKernowekIkinyarwandaIkirundiKiswahiliКомиKongoKotavaKreyòl ayisyenKriyòl gwiyannenKurdîКыргызчаКырык марыLadinLadinoЛаккуລາວLatgaļuLatinaLatviešuLëtzebuergeschЛезгиLietuviųLigureLimburgsLingálaLingua Franca NovaLivvinkarjalaLa .lojban.LugandaLombardMagyarMadhurâमैथिलीМакедонскиMalagasyമലയാളംMaltiMāoriमराठीმარგალურიمصرىဘာသာမန်مازِرونیBahasa Melayuꯃꯤꯇꯩ ꯂꯣꯟMinangkabau閩東語 / Mìng-dĕ̤ng-ngṳ̄MirandésМокшеньМонголမြန်မာဘာသာNaijáNa Vosa VakavitiNederlandsNedersaksiesNēhiyawēwin / ᓀᐦᐃᔭᐍᐏᐣनेपालीनेपाल भाषा日本語NapulitanoߒߞߏНохчийнNordfriiskNorfuk / PitkernNorsk bokmålNorsk nynorskNouormandNovialOccitanОлык марийଓଡ଼ିଆOromooOʻzbekcha / ўзбекчаਪੰਜਾਬੀPälzischپنجابیပအိုဝ်ႏဘာႏသာႏPapiamentuپښتوPatoisПерем комиភាសាខ្មែរPicardPiemontèisTok PisinPlattdüütschPolskiΠοντιακάPortuguêsQaraqalpaqshaQırımtatarcaRipoarischRomânăRomani čhibRumantschRuna SimiРусиньскыйРусскийСаха тылаGagana Samoaसंस्कृतम्SängöᱥᱟᱱᱛᱟᱲᱤسرائیکیSarduScotsSeelterskSesothoSesotho sa LeboaShqipSicilianuසිංහලSimple EnglishسنڌيSlovenčinaSlovenščinaСловѣньскъ / ⰔⰎⰑⰂⰡⰐⰠⰔⰍⰟŚlůnskiSoomaaligaکوردیSranantongoСрпски / srpskiSrpskohrvatski / српскохрватскиSundaSuomiSvenskaTagalogதமிழ்TaclḥitTaqbaylitTarandíneТатарча / tatarçaၽႃႇသႃႇတႆး TayalతెలుగుTetunไทยThuɔŋjäŋТоҷикӣLea faka-TongaᏣᎳᎩತುಳುTürkçeTürkmençeTyapТыва дылУдмуртBasa UgiУкраїнськаاردوئۇيغۇرچە / UyghurcheVahcuenghVènetoVepsän kel’Tiếng ViệtVolapükVõroWalonWayuunaiki文言West-VlamsWinarayWolof吴语XitsongaייִדישYorùbá粵語ZazakiZeêuwsŽemaitėška中文DagaareFɔ̀ngbèGhanaian PidginTolışiⵜⴰⵎⴰⵣⵉⵖⵜ ⵜⴰⵏⴰⵡⴰⵢⵜ

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From Wikipedia, the free encyclopedia

Third planet from the Sun

"Planet Earth" redirects here. For other uses, see Earth (disambiguation) and Planet Earth (disambiguation).

EarthThe Blue Marble, Apollo 17, December 1972DesignationsAlternative namesThe world, the globe, Sol III, Terra, Tellus, Gaia, Mother EarthAdjectivesEarthly, terrestrial, terran, tellurianSymbol and Orbital characteristicsEpoch J2000[n 1]Aphelion152097597 km (94509065 mi)Perihelion147098450 km (91402740 mi)[n 2]Semi-major axis149598023 km (92955902 mi)[1]Eccentricity0.0167086[1]Orbital period (sidereal)365.256363004 d[2](1.00001742096 aj)Average orbital speed29.7827 km/s[3](107218 km/h; 66622 mph)Mean anomaly358.617°Inclination7.155° – Sun's equator;1.57869° – invariable plane;[4]0.00005° – J2000 eclipticLongitude of ascending node−11.26064° – J2000 ecliptic[3]Time of perihelion2023-Jan-04[5]Argument of perihelion114.20783°[3]Satellites1, the MoonPhysical characteristicsMean radius6371.0 km (3958.8 mi)[6]Equatorial radius6378.137 km (3963.191 mi)[7][8]Polar radius6356.752 km (3949.903 mi)[9]Flattening1/298.257222101 (ETRS89)[10]Circumference40075.017 km(24901.461 mi), equatorial[8]40007.86 km (24859.73 mi), meridional[11][n 3]Surface area510072000 km2(196940000 sq mi)[12][n 4]Land: 148940000 km2(57510000 sq mi)Water: 361132000 km2(139434000 sq mi)Volume1.08321×1012 km3 (2.59876×1011 cu mi)[3]Mass5.972168×1024 kg (1.31668×1025 lb)[13]Mean density5.5134 g/cm3(0.19918 lb/cu in)[3]Surface gravity9.80665 m/s2(32.1740 ft/s2)[14]Moment of inertia factor0.3307[15]Escape velocity11.186 km/s (40270 km/h; 25020 mph)[3]Synodic rotation period1.0 d (24h 00 m 00s)Sidereal rotation period0.99726968 d[16] (23h 56 m 4.100s)Equatorial rotation velocity0.4651 km/s[17] (1674.4 km/h; 1040.4 mph)Axial tilt23.4392811°[2]Albedo0.367 geometric[3]0.306 Bond[3]Temperature255 K (−18 °C; −1 °F)(blackbody temperature)[18]

Surface temp.

min

mean

max

Celsius[n 5]

−89.2 °C

14.76 °C

56.7 °C

Fahrenheit

−128.5 °F

58.568 °F

134.0 °F

Surface equivalent dose rate0.274 μSv/h[22]Absolute magnitude (H)−3.99AtmosphereSurface pressure101.325 kPa (at sea level)Composition by volume78.08% nitrogen (dry air)20.95% oxygen (dry air)≤1% water vapor (variable)0.9340% argon0.0415% carbon dioxide0.00182% neon0.00052% helium0.00017% methane0.00011% krypton0.00006% hydrogen

Source:[3]Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is enabled by Earth being a water world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its global ocean, covering 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is land, most of which is located in the form of continental landmasses within Earth's land hemisphere. Most of Earth's land is somewhat humid and covered by vegetation, while large sheets of ice at Earth's polar deserts retain more water than Earth's groundwater, lakes, rivers and atmospheric water combined. Earth's crust consists of slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth has a liquid outer core that generates a magnetosphere capable of deflecting most of the destructive solar winds and cosmic radiation.

Earth has a dynamic atmosphere, which sustains Earth's surface conditions and protects it from most meteoroids and UV-light at entry. It has a composition of primarily nitrogen and oxygen. Water vapor is widely present in the atmosphere, forming clouds that cover most of the planet. The water vapor acts as a greenhouse gas and, together with other greenhouse gases in the atmosphere, particularly carbon dioxide (CO2), creates the conditions for both liquid surface water and water vapor to persist via the capturing of energy from the Sun's light. This process maintains the current average surface temperature of 14.76 °C, at which water is liquid under atmospheric pressure. Differences in the amount of captured energy between geographic regions (as with the equatorial region receiving more sunlight than the polar regions) drive atmospheric and ocean currents, producing a global climate system with different climate regions, and a range of weather phenomena such as precipitation, allowing components such as nitrogen to cycle.

Earth is rounded into an ellipsoid with a circumference of about 40,000 km. It is the densest planet in the Solar System. Of the four rocky planets, it is the largest and most massive. Earth is about eight light-minutes away from the Sun and orbits it, taking a year (about 365.25 days) to complete one revolution. Earth rotates around its own axis in slightly less than a day (in about 23 hours and 56 minutes). Earth's axis of rotation is tilted with respect to the perpendicular to its orbital plane around the Sun, producing seasons. Earth is orbited by one permanent natural satellite, the Moon, which orbits Earth at 384,400 km (1.28 light seconds) and is roughly a quarter as wide as Earth. The Moon's gravity helps stabilize Earth's axis, causes tides and gradually slows Earth's rotation. Tidal locking has made the Moon always face Earth with the same side.

Earth, like most other bodies in the Solar System, formed 4.5 billion years ago from gas in the early Solar System. During the first billion years of Earth's history, the ocean formed and then life developed within it. Life spread globally and has been altering Earth's atmosphere and surface, leading to the Great Oxidation Event two billion years ago. Humans emerged 300,000 years ago in Africa and have spread across every continent on Earth. Humans depend on Earth's biosphere and natural resources for their survival, but have increasingly impacted the planet's environment. Humanity's current impact on Earth's climate and biosphere is unsustainable, threatening the livelihood of humans and many other forms of life, and causing widespread extinctions.[23]

Etymology

The Modern English word Earth developed, via Middle English, from an Old English noun most often spelled eorðe.[24] It has cognates in every Germanic language, and their ancestral root has been reconstructed as *erþō. In its earliest attestation, the word eorðe was used to translate the many senses of Latin terra and Greek γῆ gē: the ground, its soil, dry land, the human world, the surface of the world (including the sea), and the globe itself. As with Roman Terra/Tellūs and Greek Gaia, Earth may have been a personified goddess in Germanic paganism: late Norse mythology included Jörð ("Earth"), a giantess often given as the mother of Thor.[25]

Historically, "Earth" has been written in lowercase. Beginning with the use of Early Middle English, its definite sense as "the globe" was expressed as "the earth". By the era of Early Modern English, capitalization of nouns began to prevail, and the earth was also written the Earth, particularly when referenced along with other heavenly bodies. More recently, the name is sometimes simply given as Earth, by analogy with the names of the other planets, though "earth" and forms with "the earth" remain common.[24] House styles now vary: Oxford spelling recognizes the lowercase form as the more common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name, such as a description of the "Earth's atmosphere", but employs the lowercase when it is preceded by "the", such as "the atmosphere of the earth"). It almost always appears in lowercase in colloquial expressions such as "what on earth are you doing?"[26]

The name Terra /ˈtɛrə/ occasionally is used in scientific writing and especially in science fiction to distinguish humanity's inhabited planet from others,[27] while in poetry Tellus /ˈtɛləs/ has been used to denote personification of the Earth.[28] Terra is also the name of the planet in some Romance languages, languages that evolved from Latin, like Italian and Portuguese, while in other Romance languages the word gave rise to names with slightly altered spellings, like the Spanish Tierra and the French Terre. The Latinate form Gæa or Gaea (English: /ˈdʒiː.ə/) of the Greek poetic name Gaia (Γαῖα; Ancient Greek: [ɡâi̯.a] or [ɡâj.ja]) is rare, though the alternative spelling Gaia has become common due to the Gaia hypothesis, in which case its pronunciation is /ˈɡaɪ.ə/ rather than the more classical English /ˈɡeɪ.ə/.[29]

There are a number of adjectives for the planet Earth. The word "earthly" is derived from "Earth". From the Latin Terra comes terran /ˈtɛrən/,[30] terrestrial /təˈrɛstriəl/,[31] and (via French) terrene /təˈriːn/,[32] and from the Latin Tellus comes tellurian /tɛˈlʊəriən/[33] and telluric.[34]

Natural history

Main articles: History of Earth and Timeline of natural history

Formation

Further information: Early Earth and Hadean

A 2012 artistic impression of the early Solar System's protoplanetary disk from which Earth and other Solar System bodies were formed

The oldest material found in the Solar System is dated to 4.5682+0.0002−0.0004 Ga (billion years) ago.[35] By 4.54±0.04 Ga the primordial Earth had formed.[36] The bodies in the Solar System formed and evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, and dust (including primordial nuclides). According to nebular theory, planetesimals formed by accretion, with the primordial Earth being estimated as likely taking anywhere from 70 to 100 million years to form.[37]

Estimates of the age of the Moon range from 4.5 Ga to significantly younger.[38] A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object with about 10% of Earth's mass, named Theia, collided with Earth.[39] It hit Earth with a glancing blow and some of its mass merged with Earth.[40][41] Between approximately 4.1 and 3.8 Ga, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth.[42]

After formation

Main article: Geological history of Earth

Earth's atmosphere and oceans were formed by volcanic activity and outgassing.[43] Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids, protoplanets, and comets.[44] Sufficient water to fill the oceans may have been on Earth since it formed.[45] In this model, atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity.[46] By 3.5 Ga, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.[47]

Pale orange dot, an artist's impression of Early Earth, featuring its tinted orange methane-rich early atmosphere[48]

As the molten outer layer of Earth cooled it formed the first solid crust, which is thought to have been mafic in composition. The first continental crust, which was more felsic in composition, formed by the partial melting of this mafic crust.[49] The presence of grains of the mineral zircon of Hadean age in Eoarchean sedimentary rocks suggests that at least some felsic crust existed as early as 4.4 Ga, only 140 Ma after Earth's formation.[50] There are two main models of how this initial small volume of continental crust evolved to reach its current abundance:[51] (1) a relatively steady growth up to the present day,[52] which is supported by the radiometric dating of continental crust globally and (2) an initial rapid growth in the volume of continental crust during the Archean, forming the bulk of the continental crust that now exists,[53][54] which is supported by isotopic evidence from hafnium in zircons and neodymium in sedimentary rocks. The two models and the data that support them can be reconciled by large-scale recycling of the continental crust, particularly during the early stages of Earth's history.[55]

New continental crust forms as a result of plate tectonics, a process ultimately driven by the continuous loss of heat from Earth's interior. Over the period of hundreds of millions of years, tectonic forces have caused areas of continental crust to group together to form supercontinents that have subsequently broken apart. At approximately 750 Ma, one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia at 600–540 Ma, then finally Pangaea, which also began to break apart at 180 Ma.[56]

The most recent pattern of ice ages began about 40 Ma,[57] and then intensified during the Pleistocene about 3 Ma.[58] High- and middle-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating about every 21,000, 41,000 and 100,000 years.[59] The Last Glacial Period, colloquially called the "last ice age", covered large parts of the continents, to the middle latitudes, in ice and ended about 11,700 years ago.[60]

Origin of life and evolution

Main articles: Origin of life, Earliest known life forms, and History of life

Chemical reactions led to the first self-replicating molecules about four billion years ago. A half billion years later, the last common ancestor of all current life arose.[61] The evolution of photosynthesis allowed the Sun's energy to be harvested directly by life forms. The resultant molecular oxygen (O2) accumulated in the atmosphere and due to interaction with ultraviolet solar radiation, formed a protective ozone layer (O3) in the upper atmosphere.[62] The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes.[63] True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized Earth's surface.[64] Among the earliest fossil evidence for life is microbial mat fossils found in 3.48 billion-year-old sandstone in Western Australia,[65] biogenic graphite found in 3.7 billion-year-old metasedimentary rocks in Western Greenland,[66] and remains of biotic material found in 4.1 billion-year-old rocks in Western Australia.[67][68] The earliest direct evidence of life on Earth is contained in 3.45 billion-year-old Australian rocks showing fossils of microorganisms.[69][70]An artist's impression of the Archean, the eon after Earth's formation, featuring round stromatolites, which are early oxygen-producing forms of life from billions of years ago. After the Late Heavy Bombardment, Earth's crust had cooled, its water-rich barren surface is marked by continents and volcanoes, with the Moon still orbiting Earth half as far as it is today, appearing 2.8 times larger and producing strong tides.[71]During the Neoproterozoic, 1000 to 539 Ma, much of Earth might have been covered in ice. This hypothesis has been termed "Snowball Earth", and it is of particular interest because it preceded the Cambrian explosion, when multicellular life forms significantly increased in complexity.[72][73] Following the Cambrian explosion, 535 Ma, there have been at least five major mass extinctions and many minor ones.[74] Apart from the proposed current Holocene extinction event, the most recent was 66 Ma, when an asteroid impact triggered the extinction of the non-avian dinosaurs and other large reptiles, but largely spared small animals such as insects, mammals, lizards and birds. Mammalian life has diversified over the past 66 Mys, and several million years ago an African ape species gained the ability to stand upright.[75][better source needed] This facilitated tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which led to the evolution of humans. The development of agriculture, and then civilization, led to humans having an influence on Earth and the nature and quantity of other life forms that continues to this day.[76]

Future

Main article: Future of Earth

See also: Global catastrophic risk

Conjectured illustration of the scorched Earth after the Sun has entered the red giant phase, about 5–7 billion years from now

Earth's expected long-term future is tied to that of the Sun. Over the next 1.1 billion years, solar luminosity will increase by 10%, and over the next 3.5 billion years by 40%.[77] Earth's increasing surface temperature will accelerate the inorganic carbon cycle, reducing CO2 concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in approximately 100–900 million years.[78][79] The lack of vegetation will result in the loss of oxygen in the atmosphere, making animal life impossible.[80] Due to the increased luminosity, Earth's mean temperature may reach 100 °C (212 °F) in 1.5 billion years, and all ocean water will evaporate and be lost to space, which may trigger a runaway greenhouse effect, within an estimated 1.6 to 3 billion years.[81] Even if the Sun were stable, a fraction of the water in the modern oceans will descend to the mantle, due to reduced steam venting from mid-ocean ridges.[81][82]

The Sun will evolve to become a red giant in about 5 billion years. Models predict that the Sun will expand to roughly 1 AU (150 million km; 93 million mi), about 250 times its present radius.[77][83] Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, Earth will move to an orbit 1.7 AU (250 million km; 160 million mi) from the Sun when the star reaches its maximum radius, otherwise, with tidal effects, it may enter the Sun's atmosphere and be vaporized.[77]

Physical characteristics

Further information: Geophysics

Size and shape

Main article: Figure of the Earth

Further information: Earth radius, Earth's circumference, Earth curvature, and Geomorphology

See also: List of highest mountains on Earth

Earth's western hemisphere showing topography relative to Earth's center instead of to mean sea level, as in common topographic maps

Earth has a rounded shape, through hydrostatic equilibrium,[84] with an average diameter of 12,742 kilometers (7,918 mi), making it the fifth largest planetary sized and largest terrestrial object of the Solar System.[85]

Due to Earth's rotation it has the shape of an ellipsoid, bulging at its Equator; its diameter is 43 kilometers (27 mi) longer there than at its poles.[86][87]

Earth's shape furthermore has local topographic variations. Though the largest local variations, like the Mariana Trench (10,925 meters or 35,843 feet below local sea level),[88] only shortens Earth's average radius by 0.17% and Mount Everest (8,848 meters or 29,029 feet above local sea level) lengthens it by only 0.14%.[n 6][90] Since Earth's surface is farthest out from Earth's center of mass at its equatorial bulge, the summit of the volcano Chimborazo in Ecuador (6,384.4 km or 3,967.1 mi) is its farthest point out.[91][92]

Parallel to the rigid land topography the Ocean exhibits a more dynamic topography.[93]

To measure the local variation of Earth's topography, geodesy employs an idealized Earth producing a shape called a geoid. Such a geoid shape is gained if the ocean is idealized, covering Earth completely and without any perturbations such as tides and winds. The result is a smooth but gravitational irregular geoid surface, providing a mean sea level (MSL) as a reference level for topographic measurements.[94]

Surface

Further information: Planetary surface, Land cover, Land, Pedosphere, Ocean, Sea, Cryosphere, and Peplosphere

A composite image of Earth, with its different types of surface discernible: Earth's surface dominating Ocean (blue), Africa with lush (green) to dry (brown) land and Earth's polar ice in the form of Antarctic sea ice (grey) covering the Antarctic or Southern Ocean and the Antarctic ice sheet (white) covering Antarctica.

Relief of Earth's crust

Earth's surface is the boundary between the atmosphere, and the solid Earth and oceans. Defined in this way, it has an area of about 510 million km2 (197 million sq mi).[12] Earth can be divided into two hemispheres: by latitude into the polar Northern and Southern hemispheres; or by longitude into the continental Eastern and Western hemispheres.

Most of Earth's surface is ocean water: 70.8% or 361 million km2 (139 million sq mi).[95] This vast pool of salty water is often called the world ocean,[96][97] and makes Earth with its dynamic hydrosphere a water world[98][99] or ocean world.[100][101] Indeed, in Earth's early history the ocean may have covered Earth completely.[102] The world ocean is commonly divided into the Pacific Ocean, Atlantic Ocean, Indian Ocean, Antarctic or Southern Ocean, and Arctic Ocean, from largest to smallest. The ocean covers Earth's oceanic crust, but to a lesser extent with shelf seas also shelves of the continental crust. The oceanic crust forms large oceanic basins with features like abyssal plains, seamounts, submarine volcanoes,[86] oceanic trenches, submarine canyons, oceanic plateaus, and a globe-spanning mid-ocean ridge system.

At Earth's polar regions, the ocean surface is covered by seasonally variable amounts of sea ice that often connects with polar land, permafrost and ice sheets, forming polar ice caps.

Earth's land covers 29.2%, or 149 million km2 (58 million sq mi) of Earth's surface. The land surface includes many islands around the globe, but most of the land surface is taken by the four continental landmasses, which are (in descending order): Africa-Eurasia, America (landmass), Antarctica, and Australia (landmass).[103][104][105] These landmasses are further broken down and grouped into the continents. The terrain of the land surface varies greatly and consists of mountains, deserts, plains, plateaus, and other landforms. The elevation of the land surface varies from a low point of −418 m (−1,371 ft) at the Dead Sea, to a maximum altitude of 8,848 m (29,029 ft) at the top of Mount Everest. The mean height of land above sea level is about 797 m (2,615 ft).[106]

Land can be covered by surface water, snow, ice, artificial structures or vegetation. Most of Earth's land hosts vegetation,[107] but ice sheets (10%,[108] not including the equally large land under permafrost)[109] or cold as well as hot deserts (33%)[110] occupy also considerable amounts of it.

The pedosphere is the outermost layer of Earth's land surface and is composed of soil and subject to soil formation processes. Soil is crucial for land to be arable. Earth's total arable land is 10.7% of the land surface, with 1.3% being permanent cropland.[111][112] Earth has an estimated 16.7 million km2 (6.4 million sq mi) of cropland and 33.5 million km2 (12.9 million sq mi) of pastureland.[113]

The land surface and the ocean floor form the top of Earth's crust, which together with parts of the upper mantle form Earth's lithosphere. Earth's crust may be divided into oceanic and continental crust. Beneath the ocean-floor sediments, the oceanic crust is predominantly basaltic, while the continental crust may include lower density materials such as granite, sediments and metamorphic rocks.[114] Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form about 5% of the mass of the crust.[115]

Earth's surface topography comprises both the topography of the ocean surface, and the shape of Earth's land surface. The submarine terrain of the ocean floor has an average bathymetric depth of 4 km, and is as varied as the terrain above sea level.

Earth's surface is continually being shaped by internal plate tectonic processes including earthquakes and volcanism; by weathering and erosion driven by ice, water, wind and temperature; and by biological processes including the growth and decomposition of biomass into soil.[116][117]

Tectonic plates

Main article: Plate tectonics

Earth's major plates, which are:[118] Pacific Plate African Plate[n 7] North American Plate Eurasian Plate Antarctic Plate Indo-Australian Plate South American Plate

Earth's mechanically rigid outer layer of Earth's crust and upper mantle, the lithosphere, is divided into tectonic plates. These plates are rigid segments that move relative to each other at one of three boundaries types: at convergent boundaries, two plates come together; at divergent boundaries, two plates are pulled apart; and at transform boundaries, two plates slide past one another laterally. Along these plate boundaries, earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur.[119] 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.[120]

As the tectonic plates migrate, oceanic crust is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes recycles the oceanic crust back into the mantle. Due to this recycling, most of the ocean floor is less than 100 Ma old. The oldest oceanic crust is located in the Western Pacific and is estimated to be 200 Ma old.[121][122] By comparison, the oldest dated continental crust is 4,030 Ma,[123] although zircons have been found preserved as clasts within Eoarchean sedimentary rocks that give ages up to 4,400 Ma, indicating that at least some continental crust existed at that time.[50]

The seven major plates are the Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, and South American. Other notable plates include the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. The Australian Plate fused with the Indian Plate between 50 and 55 Ma. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/a (3.0 in/year)[124] and the Pacific Plate moving 52–69 mm/a (2.0–2.7 in/year). At the other extreme, the slowest-moving plate is the South American Plate, progressing at a typical rate of 10.6 mm/a (0.42 in/year).[125]

Internal structure

Main article: Internal structure of Earth

Geologic layers of Earth[126]

Illustration of Earth's cutaway, not to scale

Depth[127](km)

Component layer name

Density(g/cm3)

0–60

Lithosphere[n 8]

—

0–35

Crust[n 9]

2.2–2.9

35–660

Upper mantle

3.4–4.4

660–2890

Lower mantle

3.4–5.6

100–700

Asthenosphere

—

2890–5100

Outer core

9.9–12.2

5100–6378

Inner core

12.8–13.1

Earth's interior, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties. The outer layer is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity.[128] The thickness of the crust varies from about 6 kilometers (3.7 mi) under the oceans to 30–50 km (19–31 mi) for the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, which is divided into independently moving tectonic plates.[129]

Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 km (250 and 410 mi) below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core.[130] Earth's inner core may be rotating at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year, although both somewhat higher and much lower rates have also been proposed.[131] The radius of the inner core is about one-fifth of that of Earth.

Density increases with depth, as described in the table on the right.

Among the Solar System's planetary-sized objects Earth is the object with the highest density.

Chemical composition

See also: Abundance of elements on Earth

Earth's mass is approximately 5.97×1024 kg (5,970 Yg). It is composed mostly of iron (32.1% by mass), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminum (1.4%), with the remaining 1.2% consisting of trace amounts of other elements. Due to gravitational separation, the core is primarily composed of the denser elements: iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.[132][49] The most common rock constituents of the crust are oxides. Over 99% of the crust is composed of various oxides of eleven elements, principally oxides containing silicon (the silicate minerals), aluminum, iron, calcium, magnesium, potassium, or sodium.[133][132]

Internal heat

Main article: Earth's internal heat budget

A map of heat flow from Earth's interior to the surface of Earth's crust, mostly along the oceanic ridges

The major heat-producing isotopes within Earth are potassium-40, uranium-238, and thorium-232.[134] At the center, the temperature may be up to 6,000 °C (10,830 °F),[135] and the pressure could reach 360 GPa (52 million psi).[136] Because much of the heat is provided by radioactive decay, scientists postulate that early in Earth's history, before isotopes with short half-lives were depleted, Earth's heat production was much higher. At approximately 3 Gyr, twice the present-day heat would have been produced, increasing the rates of mantle convection and plate tectonics, and allowing the production of uncommon igneous rocks such as komatiites that are rarely formed today.[137][138]

The mean heat loss from Earth is 87 mW m−2, for a global heat loss of 4.42×1013 W.[139] 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.[140] More of the heat in 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 under the oceans because the crust there is much thinner than that of the continents.[141]

Gravitational field

Main article: Gravity of Earth

The gravity of Earth is the acceleration that is imparted to objects due to the distribution of mass within Earth. Near Earth's surface, gravitational acceleration is approximately 9.8 m/s2 (32 ft/s2). Local differences in topography, geology, and deeper tectonic structure cause local and broad regional differences in Earth's gravitational field, known as gravity anomalies.[142]

Magnetic field

Main article: Earth's magnetic field

A schematic view of Earth's magnetosphere with solar wind flowing from left to right

The main part of Earth's magnetic field is generated in the core, the site of a dynamo process that converts the kinetic energy of thermally and compositionally driven convection into electrical and magnetic field energy. The field extends outwards from the core, through the mantle, and up to Earth's surface, where it is, approximately, a dipole. The poles of the dipole are located close to Earth's geographic poles. At the equator of the magnetic field, the magnetic-field strength at the surface is 3.05×10−5 T, with a magnetic dipole moment of 7.79×1022 Am2 at epoch 2000, decreasing nearly 6% per century (although it still remains stronger than its long time average).[143] The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes secular variation of the main field and field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.[144][145]

The extent of Earth's magnetic field in space defines the magnetosphere. Ions and electrons of the solar wind are deflected by the magnetosphere; solar wind pressure compresses the dayside of the magnetosphere, to about 10 Earth radii, and extends the nightside magnetosphere into a long tail.[146] Because the velocity of the solar wind is greater than the speed at which waves propagate through the solar wind, a supersonic bow shock precedes the dayside magnetosphere within the solar wind.[147] Charged particles are contained within the magnetosphere; the plasmasphere is defined by low-energy particles that essentially follow magnetic field lines as Earth rotates.[148][149] The ring current is defined by medium-energy particles that drift relative to the geomagnetic field, but with paths that are still dominated by the magnetic field,[150] and the Van Allen radiation belts are formed by high-energy particles whose motion is essentially random, but contained in the magnetosphere.[151][152]

During magnetic storms and substorms, charged particles can be deflected from the outer magnetosphere and especially the magnetotail, directed along field lines into Earth's ionosphere, where atmospheric atoms can be excited and ionized, causing the aurora.[153]

Orbit and rotation

Rotation

Main article: Earth's rotation

Satellite time lapse imagery of Earth's rotation showing axis tilt

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).[154] Because Earth's solar day is now slightly longer than it was during the 19th century due to tidal deceleration, each day varies between 0 and 2 ms longer than the mean solar day.[155][156]

Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86,164.0989 seconds of mean solar time (UT1), or 23h 56m 4.0989s.[2][n 10] Earth's rotation period relative to the precessing or moving mean March equinox (when the Sun is at 90° on the equator), is 86,164.0905 seconds of mean solar time (UT1) (23h 56m 4.0905s).[2] Thus the sidereal day is shorter than the stellar day by about 8.4 ms.[157]

Apart from meteors within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in 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 the Moon every two minutes; from Earth's surface, the apparent sizes of the Sun and the Moon are approximately the same.[158][159]

Orbit

Main articles: Earth's orbit and Earth's location

Exaggerated illustration of Earth's elliptical orbit around the Sun, marking that the orbital extreme points (apoapsis and periapsis) are not the same as the four seasonal extreme points, the equinox and solstice

Earth orbits the Sun, making Earth the third-closest planet to the Sun and part of the inner Solar System. Earth's average orbital distance is about 150 million km (93 million mi), which is the basis for the Astronomical Unit and is equal to roughly 8.3 light minutes or 380 times Earth's distance to the Moon.

Earth orbits the Sun every 365.2564 mean solar days, or one sidereal year. With an apparent movement of the Sun in Earth's sky at a rate of about 1°/day eastward, which is one apparent Sun or Moon diameter every 12 hours. Due to 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 Earth averages about 29.78 km/s (107,200 km/h; 66,600 mph), which is fast enough to travel a distance equal to Earth's diameter, about 12,742 km (7,918 mi), in seven minutes, and the distance to the Moon, 384,000 km (239,000 mi), in about 3.5 hours.[3]

The Moon and Earth orbit a common barycenter every 27.32 days relative to the background stars. When combined with the Earth–Moon system's common orbit 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 counterclockwise. Viewed from a vantage point above the Sun and Earth's north poles, Earth orbits in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.44 degrees from the perpendicular to the Earth–Sun plane (the ecliptic), and the Earth-Moon plane is tilted up to ±5.1 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][160]

The Hill sphere, or the sphere of gravitational influence, of Earth is about 1.5 million km (930,000 mi) in radius.[161][n 11] This is the maximum distance at which Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.[161] Earth, along with the Solar System, is situated in the Milky Way and orbits about 28,000 light-years from its center. It is about 20 light-years above the galactic plane in the Orion Arm.[162]

Axial tilt and seasons

Main article: Axial tilt § Earth

Earth's axial tilt causing different angles of seasonal illumination at different orbital positions around the Sun

The axial tilt of Earth is approximately 23.439281°[2] with the axis of its orbit plane, always pointing towards the Celestial Poles. Due to Earth's axial tilt, the amount of sunlight reaching any given point on the surface varies over the course of the year. This causes the seasonal change in climate, with summer in the Northern Hemisphere occurring when the Tropic of Cancer is facing the Sun, and in the Southern Hemisphere when the Tropic of Capricorn faces the Sun. In each instance, winter occurs simultaneously in the opposite hemisphere.

During the summer, the day lasts longer, and the Sun climbs higher in the sky. In winter, the climate becomes cooler and the days shorter.[163] Above the Arctic Circle and below the Antarctic Circle there is no daylight at all for part of the year, causing a polar night, and this night extends for several months at the poles themselves. These same latitudes also experience a midnight sun, where the sun remains visible all day.[164][165]

By astronomical convention, the four seasons can be determined by the solstices—the points in the orbit of maximum axial tilt toward or away from the Sun—and the equinoxes, when Earth's rotational axis is aligned with its orbital axis. In the Northern Hemisphere, winter solstice currently occurs around 21 December; summer solstice is near 21 June, spring equinox is around 20 March and autumnal equinox is about 22 or 23 September. In the Southern Hemisphere, the situation is reversed, with the summer and winter solstices exchanged and the spring and autumnal equinox dates swapped.[166]

The angle of Earth's axial tilt is relatively stable over long periods of time. Its axial tilt does undergo nutation; a slight, irregular motion with a main period of 18.6 years.[167] The orientation (rather than the angle) of Earth's axis also changes over time, precessing around in a complete circle over each 25,800-year cycle; this precession is the reason for the difference between a sidereal year and a tropical year. Both of these motions are caused by the varying attraction of the Sun and the Moon on Earth's equatorial bulge. The poles also migrate a few meters across Earth's surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. Earth's rotational velocity also varies in a phenomenon known as length-of-day variation.[168]

In modern times, Earth's perihelion occurs around 3 January, and its aphelion around 4 July. 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 causes an increase of about 6.8% in solar energy reaching Earth at perihelion relative to aphelion.[169][n 12] Because the Southern Hemisphere is tilted toward the Sun at about the same time that 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 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.[170]

Earth–Moon system

Further information: Satellite system (astronomy)

Moon

Main articles: Moon, Lunar theory, and Orbit of the Moon

Earth and the Moon as seen from Mars by the Mars Reconnaissance Orbiter

View of Earth from the Moon by the Lunar Reconnaissance Orbiter

The Moon is a relatively large, terrestrial, planet-like natural satellite, with a diameter about one-quarter of Earth's. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger relative to the dwarf planet Pluto.[171][172] The natural satellites of other planets are also referred to as "moons", after Earth's.[173] The most widely accepted theory of the Moon's origin, the giant-impact hypothesis, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. This hypothesis explains the Moon's relative lack of iron and volatile elements and the fact that its composition is nearly identical to that of Earth's crust.[40]

The gravitational attraction between Earth and the Moon causes tides on Earth.[174] The same effect on the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit Earth. As a result, it always presents the same face to the planet.[175] As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases.[176] Due to their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm/a (1.5 in/year). Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23 µs/yr—add up to significant changes.[177] During the Ediacaran period, for example, (approximately 620 Ma) there were 400±7 days in a year, with each day lasting 21.9±0.4 hours.[178]

The Moon may have dramatically affected the development of life by moderating the planet's climate. Paleontological evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon.[179] Some theorists think that without this stabilization against the torques applied by the Sun and planets to Earth's equatorial bulge, the rotational axis might be chaotically unstable, exhibiting large changes over millions of years, as is the case for Mars, though this is disputed.[180][181]

Viewed from Earth, the Moon is just far enough away to have almost the same apparent-sized disk as the Sun. The angular size (or solid angle) of these two bodies match because, although the Sun's diameter is about 400 times as large as the Moon's, it is also 400 times more distant.[159] This allows total and annular solar eclipses to occur on Earth.[182]

On 1 November 2023, scientists reported that, according to computer simulations, remnants of a protoplanet, named Theia, could be inside the Earth, left over from a collision with the Earth in ancient times, and afterwards becoming the Moon.[183][184]

Asteroids and artificial satellites

Main articles: Near-Earth object and Claimed moons of Earth

A computer-generated image mapping the prevalence of artificial satellites and space debris around Earth in geosynchronous and low Earth orbit

Earth's co-orbital asteroids population consists of quasi-satellites, objects with a horseshoe orbit and trojans. There are at least five quasi-satellites, including 469219 Kamoʻoalewa.[185][186] A trojan asteroid companion, 2010 TK7, is librating around the leading Lagrange triangular point, L4, in Earth's orbit around the Sun.[187] The tiny near-Earth asteroid 2006 RH120 makes close approaches to the Earth–Moon system roughly every twenty years. During these approaches, it can orbit Earth for brief periods of time.[188]

As of September 2021[update], there are 4,550 operational, human-made satellites orbiting Earth.[189] There are also inoperative satellites, including Vanguard 1, the oldest satellite currently in orbit, and over 16,000 pieces of tracked space debris.[n 13] Earth's largest artificial satellite is the International Space Station.[190]

Hydrosphere

Main article: Hydrosphere

A view of Earth with its global ocean and cloud cover, which dominate Earth's surface and hydrosphere; at Earth's polar regions, its hydrosphere forms larger areas of ice cover.

Earth's hydrosphere is the sum of Earth's water and its distribution. Most of Earth's hydrosphere consists of Earth's global ocean. Earth's hydrosphere also consists of water in the atmosphere and on land, including clouds, inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m (6,600 ft).

The mass of the oceans is approximately 1.35×1018 metric tons or about 1/4400 of Earth's total mass. The oceans cover an area of 361.8 million km2 (139.7 million sq mi) with a mean depth of 3,682 m (12,080 ft), resulting in an estimated volume of 1.332 billion km3 (320 million cu mi).[191] If all of Earth's crustal surface were at the same elevation as a smooth sphere, the depth of the resulting world ocean would be 2.7 to 2.8 km (1.68 to 1.74 mi).[192] About 97.5% of the water is saline; the remaining 2.5% is fresh water.[193][194] Most fresh water, about 68.7%, is present as ice in ice caps and glaciers.[195] The remaining 30% is ground water, 1% surface water (covering only 2.8% of Earth's land)[196] and other small forms of fresh water deposits such as permafrost, water vapor in the atmosphere, biological binding, etc. .[197][198]

In Earth's coldest regions, snow survives over the summer and changes into ice. This accumulated snow and ice eventually forms into glaciers, bodies of ice that flow under the influence of their own gravity. Alpine glaciers form in mountainous areas, whereas vast ice sheets form over land in polar regions. The flow of glaciers erodes the surface changing it dramatically, with the formation of U-shaped valleys and other landforms.[199] Sea ice in the Arctic covers an area about as big as the United States, although it is quickly retreating as a consequence of climate change.[200]

The average salinity of Earth's oceans is about 35 grams of salt per kilogram of seawater (3.5% salt).[201] Most of this salt was released from volcanic activity or extracted from cool igneous rocks.[202] The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms.[203] Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir.[204] Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño–Southern Oscillation.[205]

The abundance of water, particularly liquid water, on Earth's surface is a unique feature that distinguishes it from other planets in the Solar System. Solar System planets with considerable atmospheres do partly host atmospheric water vapor, but they lack surface conditions for stable surface water.[206] Despite some moons showing signs of large reservoirs of extraterrestrial liquid water, with possibly even more volume than Earth's ocean, all of them are large bodies of water under a kilometers thick frozen surface layer.[207]

Atmosphere

Main article: Atmosphere of Earth

A view of Earth with different layers of its atmosphere visible: the troposphere with its clouds casting shadows, a band of stratospheric blue sky at the horizon, and a line of green airglow of the lower thermosphere around an altitude of 100 km, at the edge of space

The atmospheric pressure at Earth's sea level averages 101.325 kPa (14.696 psi),[208] with a scale height of about 8.5 km (5.3 mi).[3] A dry atmosphere is composed of 78.084% nitrogen, 20.946% oxygen, 0.934% argon, and trace amounts of carbon dioxide and other gaseous molecules.[208] Water vapor content varies between 0.01% and 4%[208] but averages about 1%.[3] Clouds cover around two-thirds of Earth's surface, more so over oceans than land.[209] The height of the troposphere varies with latitude, ranging between 8 km (5 mi) at the poles to 17 km (11 mi) at the equator, with some variation resulting from weather and seasonal factors.[210]

Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 Gya, forming the primarily nitrogen–oxygen atmosphere of today.[62] This change enabled the proliferation of aerobic organisms and, indirectly, the formation of the ozone layer due to the subsequent conversion of atmospheric O2 into O3. The ozone layer blocks ultraviolet solar radiation, permitting life on land.[211] Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature.[212] This last phenomenon is the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the surface, thereby raising the average temperature. Water vapor, carbon dioxide, methane, nitrous oxide, and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C (0 °F), in contrast to the current +15 °C (59 °F),[213] and life on Earth probably would not exist in its current form.[214]

Weather and climate

Main articles: Weather and Climate

The ITCZ's band of clouds over the Eastern Pacific and the Americas as seen from spaceWorldwide Köppen climate classifications

Earth's atmosphere has no definite boundary, gradually becoming thinner and fading into outer space.[215] Three-quarters of the atmosphere's mass is contained within the first 11 km (6.8 mi) of the surface; this lowest layer is called the troposphere.[216] 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 thermal energy.[217]

The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°.[218] Ocean heat content and currents are also important factors in determining climate, particularly the thermohaline circulation that distributes thermal energy from the equatorial oceans to the polar regions.[219]

Earth receives 1361 W/m2 of solar irradiance.[220][221] The amount of solar energy that reaches Earth's surface decreases with increasing latitude. At higher latitudes, the sunlight reaches the surface at 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 (0.7 °F) per degree of latitude from the equator.[222] Earth's surface can be subdivided 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.[223]

Further factors that affect a location's climates are its proximity to oceans, the oceanic and atmospheric circulation, and topology.[224] Places close to oceans typically have colder summers and warmer winters, due to the fact that oceans can store large amounts of heat. The wind transports the cold or the heat of the ocean to the land.[225] Atmospheric circulation also plays an important role: San Francisco and Washington DC are both coastal cities at about the same latitude. San Francisco's climate is significantly more moderate as the prevailing wind direction is from sea to land.[226] Finally, temperatures decrease with height causing mountainous areas to be colder than low-lying areas.[227]

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 falls to the surface as precipitation.[217] 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, topographic features, and temperature differences determine the average precipitation that falls in each region.[228]

The commonly used Köppen climate classification system has five broad groups (humid tropics, arid, humid middle latitudes, continental and cold polar), which are further divided into more specific subtypes.[218] The Köppen system rates regions based on observed temperature and precipitation.[229] Surface air temperature can rise to around 55 °C (131 °F) in hot deserts, such as Death Valley, and can fall as low as −89 °C (−128 °F) in Antarctica.[230][231]

Upper atmosphere

Earth's atmosphere as it appears from space, as bands of different colours at the horizon. From the bottom, afterglow illuminates the troposphere in orange with silhouettes of clouds, and the stratosphere in white and blue. Next the mesosphere (pink area) extends to just below the edge of space at one hundred kilometers and the pink line of airglow of the lower thermosphere (invisible), which hosts green and red aurorae over several hundred kilometers.

The upper atmosphere, the atmosphere above the troposphere,[232] is usually divided into the stratosphere, mesosphere, and thermosphere.[212] 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 geomagnetic fields interact with the solar wind.[233] Within the stratosphere is the ozone layer, a component that partially shields the surface from ultraviolet light and thus is important for life on Earth. The Kármán line, defined as 100 km (62 mi) above Earth's surface, is a working definition for the boundary between the atmosphere and outer space.[234]

Thermal energy causes some of the molecules at the outer edge of the atmosphere to increase their velocity to the point where they can escape from Earth's gravity. This causes a slow but steady loss of the atmosphere into space. Because unfixed hydrogen has a low molecular mass, it can achieve escape velocity more readily, and it leaks into outer space at a greater rate than other gases.[235] The leakage of hydrogen into space contributes to the shifting of Earth's atmosphere and surface from an initially reducing state to its current oxidizing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is thought to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere.[236] Hence the ability of hydrogen to escape from the atmosphere may have influenced the nature of life that developed on Earth.[237] 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.[238]

Life on Earth

Main articles: Biosphere and History of life

An animation of the changing density of productive vegetation on land (low in brown; heavy in dark green) and phytoplankton at the ocean surface (low in purple; high in yellow)

Earth is the only known place that has ever been habitable for life. Earth's life developed in Earth's early bodies of water some hundred million years after Earth formed.

Earth's life has been shaping and inhabiting many particular ecosystems on Earth and has eventually expanded globally forming an overarching biosphere.[239] Therefore, life has impacted Earth, significantly altering Earth's atmosphere and surface over long periods of time, causing changes like the Great Oxidation Event.[240]

Earth's life has over time greatly diversified, allowing the biosphere to have different biomes, which are inhabited by comparatively similar plants and animals.[241] The different biomes developed at distinct elevations or water depths, planetary temperature latitudes and on land also with different humidity. Earth's species diversity and biomass reaches a peak in shallow waters and with forests, particularly in equatorial, warm and humid conditions. While freezing polar regions and high altitudes, or extremely arid areas are relatively barren of plant and animal life.[242]

Earth provides liquid water—an environment where complex organic molecules can assemble and interact, and sufficient energy to sustain a metabolism.[243] Plants and other organisms take up nutrients from water, soils and the atmosphere. These nutrients are constantly recycled between different species.[244]A High Desert storm, sweeps across the Mojave

Extreme weather, such as tropical cyclones (including hurricanes and typhoons), occurs over most of Earth's surface and has a large impact on life in those areas. From 1980 to 2000, these events caused an average of 11,800 human deaths per year.[245] Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, blizzards, floods, droughts, wildfires, and other calamities and disasters.[246] Human impact is felt in many areas due to pollution of the air and water, acid rain, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion and erosion.[247] Human activities release greenhouse gases into the atmosphere which cause global warming.[248] This is driving changes such as the melting of glaciers and ice sheets, a global rise in average sea levels, increased risk of drought and wildfires, and migration of species to colder areas.[249]

Human geography

Main article: Human geography

See also

Celestial sphere

Earth phase

Earth science

Extremes on Earth

List of Solar System extremes

Outline of Earth

Table of physical properties of planets in the Solar System

Timeline of the far future

Notes

^ All astronomical quantities vary, both secularly and periodically. The quantities given are the values at the instant J2000.0 of the secular variation, ignoring all periodic variations.

^ aphelion = a × (1 + e); perihelion = a × (1 – e), where a is the semi-major axis and e is the eccentricity. The difference between Earth's perihelion and aphelion is 5 million kilometers.—Wilkinson, John (2009). Probing the New Solar System. CSIRO Publishing. p. 144. ISBN 978-0-643-09949-4.

^ Earth's circumference is almost exactly 40,000 km because the meter was calibrated on this measurement—more specifically, 1/10-millionth of the distance between the poles and the equator.

^ Due to natural fluctuations, ambiguities surrounding ice shelves, and mapping conventions for vertical datums, exact values for land and ocean coverage are not meaningful. Based on data from the Vector Map and Global Landcover Archived 26 March 2015 at the Wayback Machine datasets, extreme values for coverage of lakes and streams are 0.6% and 1.0% of Earth's surface. The ice sheets of Antarctica and Greenland are counted as land, even though much of the rock that supports them lies below sea level.

^ Source for minimum,[19] mean,[20] and maximum[21] surface temperature

^ If Earth were shrunk to the size of a billiard ball, some areas of Earth such as large mountain ranges and oceanic trenches would feel like tiny imperfections, whereas much of the planet, including the Great Plains and the abyssal plains, would feel smoother.[89]

^ Including the Somali Plate, which is being formed out of the African Plate. See: Chorowicz, Jean (October 2005). "The East African rift system". Journal of African Earth Sciences. 43 (1–3): 379–410. Bibcode:2005JAfES..43..379C. doi:10.1016/j.jafrearsci.2005.07.019.

^ Locally varies between 5 and 200 km.

^ Locally varies between 5 and 70 km.

^ The ultimate source of these figures, uses the term "seconds of UT1" instead of "seconds of mean solar time".—Aoki, S.; Kinoshita, H.; Guinot, B.; Kaplan, G. H.; McCarthy, D. D.; Seidelmann, P. K. (1982). "The new definition of universal time". Astronomy and Astrophysics. 105 (2): 359–361. Bibcode:1982A&A...105..359A.

^ For Earth, the Hill radius is

(

)

{\displaystyle R_{H}=a\left({\frac {m}{3M}}\right)^{\frac {1}{3}}}

, where m is the mass of Earth, a is an astronomical unit, and M is the mass of the Sun. So the radius in AU is about

(

⋅

332

946

)

0.01

{\displaystyle \left({\frac {1}{3\cdot 332,946}}\right)^{\frac {1}{3}}=0.01}

^ Aphelion is 103.4% of the distance to perihelion. Due to the inverse square law, the radiation at perihelion is about 106.9% of the energy at aphelion.

^ As of 4 January 2018, the United States Strategic Command tracked a total of 18,835 artificial objects, mostly debris. See: Anz-Meador, Phillip; Shoots, Debi, eds. (February 2018). "Satellite Box Score" (PDF). Orbital Debris Quarterly News. 22 (1): 12. Retrieved 18 April 2018.

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Earth

hEducationSign InMenuDonateENCYCLOPEDIC ENTRYENCYCLOPEDIC ENTRYEarthEarthEarth is the planet we live on, the third of eight planets in our solar system and the only known place in the universe to support life.Grades5 - 8SubjectsEarth Science, Astronomy, Geology, Geography, Physical Geography‌‌‌‌‌‌‌‌‌‌‌‌‌‌Loading ...ArticleVocabularyLearning materialsMapsThe active outer shell of Earth is dominated by tectonic plates, whose interactions result in volcanic eruptions, earthquakes, and geysers. Click to visit MapMaker Interactive's layer on Earth's tectonic plates.Earth is the planet we live on, one of eight planets in our solar system and the only known place in the universe to support life. Earth is the third planet from the sun, after Mercury and Venus, and before Mars. It is about 150 million kilometers (about 93 million miles) from the sun. This distance, called an astronomical unit (AU), is a standard unit of measurement in astronomy. Earth is one AU from the sun. The planet Jupiter is about 5.2 AU from the sun—about 778 million kilometers (483.5 million miles). Earth is the largest and most massive of the rocky inner planets, although it is dwarfed by the gas giants beyond the Asteroid Belt. Its diameter is about 12,700 kilometers (7,900 miles), and its mass is about 5.97×1024 kilograms (6.58×1021 tons). In contrast, Jupiter, the largest planet in the solar system, has a diameter of 143,000 kilometers (88,850 miles), and its mass is about 1,898×1024 kilograms (2093×1021 tons).Earth is an oblate spheroid. This means it is spherical in shape, but not perfectly round. It has a slightly greater radius at the Equator, the imaginary line running horizontally around the middle of the planet. In addition to bulging in the middle, Earth’s poles are slightly flattened. The geoid describes the model shape of Earth, and is used to calculate precise surface locations.Earth has one natural satellite, the moon. Earth is the only planet in the solar system to have one moon. Venus and Mercury do not have any moons, for example, while Jupiter and Saturn each have more than a dozen. Planet Earth InteriorEarth’s interior is a complex structure of superheated rocks. Most geologists recognize three major layers: the dense core, the bulky mantle, and the brittle crust. No one has ever ventured below Earth’s crust. Earth’s core is mostly made of iron and nickel. It consists of a solid center surrounded by an outer layer of liquid. The core is found about 2,900 kilometers (1,802 miles) below Earth’s surface, and has a radius of about 3,485 kilometers (2,165 miles). A mantle of heavy rock (mostly silicates) surrounds the core. The mantle is about 2,900 kilometers (1,802 miles) thick, and makes up a whopping 84 percent of Earth’s total volume. Parts of the mantle are molten, meaning they are composed of partly melted rock. The mantle’s molten rock is constantly in motion. It is forced to the surface during volcanic eruptions and at mid-ocean ridges. Earth’s crust is the planet’s thinnest layer, accounting for just one percent of Earth’s mass. There are two kinds of crust: thin, dense oceanic crust and thick, less-dense continental crust. Oceanic crust extends about five to 10 kilometers (three to six miles) beneath the ocean floor. Continental crust is about 35 to 70 kilometers (22 to 44 miles) thick. Exterior: Tectonic ActivityThe crust is covered by a series of constantly moving tectonic plates. New crust is created along mid-ocean ridges and rift valleys, where plates pull apart from each other in a process called rifting. Plates slide above and below each other in a process called subduction. They crash against each other in a process called faulting. Tectonic activity such as subduction and faulting has shaped the crust into a variety of landscapes. Earth’s highest point is Mount Everest, Nepal, which soars 8,850 kilometers (29,035 feet) in the Himalaya Mountains in Asia. Mount Everest continues to grow every year, as subduction drives the Indo-Australian tectonic plate below the Eurasian tectonic plate. Subduction also creates Earth’s deepest point, the Mariana Trench, about 11 kilometers (6.9 miles) below the surface of the Pacific Ocean. The heavy Pacific plate is being subducted beneath the small Mariana plate. Plate tectonics are also responsible for landforms such as geysers, earthquakes, and volcanoes. Tectonic activity around the Pacific plate, for instance, creates the Ring of Fire. This tectonically active area includes volcanoes such as Mount Fuji, Japan, and earthquake-prone fault zones such as the west coast of the United States. Revolution and RotationEarth is a rocky body constantly moving around the sun in a path called an orbit. Earth and the moon follow a slightly oval-shaped orbit around the sun every year. Each journey around the sun, a trip of about 940 million kilometers (584 million miles), is called a revolution. A year on Earth is the time it takes to complete one revolution, about 365.25 days. Earth orbits the sun at a speedy rate of about 30 kilometers per second (18.5 miles per second). At the same time that it revolves around the sun, Earth rotates on its own axis. Rotation is when an object, such as a planet, turns around an invisible line running down its center. Earth’s axis is vertical, running from the North Pole to the South Pole. Earth makes one complete rotation about every 24 hours. Earth rotates unevenly, spinning faster at the Equator than at the poles. At the Equator, Earth rotates at about 1,670 kilometers per hour (1,040 miles per hour), while at 45° north, for example, (the approximate latitude of Green Bay, Wisconsin, United States) Earth rotates at 1,180 kilometers per hour (733 miles per hour). Earth’s rotation causes the periods of light and darkness we call day and night. The part of Earth facing the sun is in daylight; the part facing away from the sun is in darkness. If Earth did not rotate, one-half of Earth would always be too hot to support life, and the other half would be frozen. Earth rotates from west to east, so the sun appears to rise in the east and set in the west. In addition to Earth’s revolution and rotation periods, we experience light and darkness due to Earth’s axis not being straight up-and-down. Earth’s axis of rotation is tilted 23.5°. This tilt influences temperature changes and other weather patterns from season to season.The Spheres Earth’s physical environment is often described in terms of spheres: the magnetosphere, the atmosphere, the hydrosphere, and the lithosphere. Parts of these spheres make up the biosphere, the area of Earth where life exists. MagnetosphereEarth’s magnetosphere describes the pocket of space surrounding our planet where charged particles are controlled by Earth’s magnetic field. The charged particles that interact with Earth’s magnetosphere are called the solar wind. The pressure of the solar wind compresses the magnetosphere on the “dayside” of Earth to about 10 Earth radii. The long tail of the magnetosphere on the “nightside” of Earth stretches to hundreds of Earth radii. The most well-known aspect of the magnetosphere are the charged particles that sometimes interact over its poles—the auroras, or Northern and Southern Lights.AtmosphereEarth’s atmosphere is a blanket of gases enveloping Earth and retained by our planet’s gravity. Atmospheric gases include nitrogen, water vapor, oxygen, and carbon dioxide. The atmosphere is responsible for temperature and other weather patterns on Earth. It blocks most of the sun’s ultraviolet radiation (UV), conducts solar radiation and precipitation through constantly moving air masses, and keeps our planet’s average surface temperature to about 15° Celsius (59° Fahrenheit). The atmosphere has a layered structure. From the ground toward the sky, the layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Up to 75 percent of the total mass of the atmosphere is in the troposphere, where most weather occurs. The boundaries between the layers are not clearly defined, and change depending on latitude and season.HydrosphereThe hydrosphere is composed of all the water on Earth. Nearly three-fourths of Earth is covered in water, most of it in the ocean. Less than three percent of the hydrosphere is made up of freshwater. Most freshwater is frozen in ice sheets and glaciers in Antarctica, the North American island of Greenland, and the Arctic. Freshwater can also be found underground, in chambers called aquifers, as well as rivers, lakes, and springs. Water also circulates around the world as vapor. Water vapor can condense into clouds and fall back to Earth as precipitation. The hydrosphere helps regulate Earth’s temperature and climate. The ocean absorbs heat from the sun and interacts with the atmosphere to move it around Earth in air currents.LithosphereThe lithosphere is Earth’s solid shell. The crust and the upper portion of the mantle form the lithosphere. It extends from Earth’s surface to between 50 and 280 kilometers (31 to 174 miles) below it. The difference in thickness accounts for both thin oceanic and thicker continental crust. The rocks and minerals in Earth’s lithosphere are made of many elements. Rocks with oxygen and silicon, the most abundant elements in the lithosphere, are called silicates. Quartz is the most common silicate in the lithosphere—and the most common type of rock on Earth. Cycles on Earth Almost all materials on Earth are constantly being recycled. The three most common cycles are the water cycle, the carbon cycle, and the rock cycle. Water CycleThe water cycle involves three main phases, related to the three states of water: solid, liquid, and gas. Ice, or solid water, is most common near the poles and at high altitudes. Ice sheets and glaciers hold the most solid water. Ice sheets and glaciers melt, transforming into liquid water. The most abundant liquid water on the planet is in the ocean, although lakes, rivers, and underground aquifers also hold liquid water. Life on Earth is dependent on a supply of liquid water. Most organisms, in fact, are made up mostly of liquid water, called body water. The human body is about 50 percent to 60 percent body water. In addition to survival and hygiene, people use liquid water for energy and transportation. The third phase of the water cycle occurs as liquid water evaporates. Evaporation is the process of a liquid turning into a gas, or vapor. Water vapor is invisible and makes up part of the atmosphere. As water vapor condenses, or turns back into liquid, pockets of vapor become visible as clouds and fog. Eventually, clouds and fog become saturated, or full of liquid water. This liquid water falls to Earth as precipitation. It can then enter a body of water, such as an ocean or lake, or freeze and become part of a glacier or ice sheet. The water cycle starts again. Carbon CycleThe carbon cycle involves the exchange of the element carbon through Earth’s atmosphere, hydrosphere, and lithosphere. Carbon, essential for all life on Earth, enters the biosphere many ways. Carbon is one of the gases that make up the atmosphere. It is also ejected during the eruption of volcanoes and ocean vents. All living or once-living materials contain carbon. These materials are organic. Plants and other autotrophs depend on carbon dioxide to create nutrients in a process called photosynthesis. These nutrients contain carbon. Animals and other organisms that consume autotrophs obtain carbon. Fossil fuels, the remains of ancient plants and animals, contain very high amounts of carbon. As organisms die and decompose, they release carbon into the ocean, soil, or atmosphere. Plants and other autotrophs use this carbon for photosynthesis, starting the carbon cycle again.Rock CycleThe rock cycle is a process that explains the relationship between the three main types of rocks: igneous, sedimentary, and metamorphic. Unlike water in the water cycle and or carbon in the carbon cycle, not all rocks are recycled in different forms. There are some rocks that have been in their present form since soon after Earth cooled. These stable rock formations are called cratons. Igneous rocks are formed as lava hardens. Lava is molten rock ejected by volcanoes during eruptions. Granite and basalt are common types of igneous rocks. Igneous rocks can be broken apart by the forces of erosion and weathering. Winds or ocean currents may then transport these tiny rocks (sand and dust) to a different location. Sedimentary rocks are created from millions of tiny particles slowly building up over time. Igneous rocks can become sedimentary by collecting with other rocks into layers. Sedimentary rocks include sandstone and limestone. Metamorphic rocks are formed when rocks are subjected to intense heat and pressure. The rocks change (undergo metamorphosis) to become a new type of rock. Marble, for example, is a metamorphic rock created from rock that was once limestone, a sedimentary rock. Earth’s Evolution Earth and the rest of the solar system formed about 4.6 billion years ago from a huge, spinning cloud of gas and dust. Over a period of about 10 million years, the dense center of the cloud grew very hot. This massive center became the sun. The rest of the particles and objects continued to revolve around the sun, colliding with each other in clumps. Eventually, these clumps compressed into planets, asteroids, and moons. This process generated a lot of heat. Eventually, Earth began to cool and its materials began to separate. Lighter materials floated upward and formed a thin crust. Heavier materials sank toward Earth’s center. Eventually, three main layers formed: the core, the mantle, and the crust. As Earth’s internal structure developed, gases released from the interior mixed together, forming a thick, steamy atmosphere around the planet. Water vapor condensed, and was augmented by water from asteroids and comets that continued to crash to Earth. Rain began to fall and liquid water slowly filled basins in Earth’s crust, forming a primitive ocean that covered most of the planet. Today, ocean waters continue to cover nearly three-quarters of our planet. The end of Earth will come with the end of the sun. In a few billion years, the sun will no longer be able to sustain the nuclear reactions that keep its mass and luminosity consistent. First, the sun will lose more than a quarter of its mass, which will loosen its gravitational hold on Earth. Earth’s orbit will widen to about 1.7 AU. But the sun will also gain volume, expanding to about 250 times its current size. The sun in this red giant phase will drag Earth into its own fiery atmosphere, destroying the planet.Eras on EarthPaleontologists, geologists, and other scientists divide Earth’s history into time periods. The largest time period is the supereon, and only applies to one unit of time, the Precambrian. Eons, eras, and periods are smaller units of geologic time. Most of Earth’s history took place in the Precambrian, which began when Earth was cooling and ended about 542 million years ago. Life began in the Precambrian, in the forms of bacteria and other single-celled organisms. Fossils from the Precambrian are rare and difficult to study. The Precambrian supereon is usually broken into three eons: the Hadean, the Archaean, and the Proterozoic.We are currently living in the Phanerozoic eon. The first major era of the Phanerozoic is called the Paleozoic, and the Cambrian is the first period of the Paleozoic era. “The Cambrian Explosion of Life” was the rapid appearance of almost all forms of life. Paleontologists and geologists have studied fossils of archaea, bacteria, algae, fungi, plants, and animals that lived during the Cambrian period. The Cambrian was followed by the Ordovician, Silurian, Devonian, Carboniferous, and Permian periods. The Mesozoic era began about 251 million years ago. This was the era when dinosaurs flourished. The Mezozoic has three periods: the Triassic, the Jurassic, and the Cretaceous. We currently live in the Cenozoic era, which began about 65 million years ago. The Cenozoic is generally marked by three periods: the Paleogene, the Neogene, and the Quaternary. We live in the Quaternary period, which began about 2.5 million years ago. All ancestors of Homo sapiens (modern humans) evolved during the Quaternary.Fast FactEarth by the NumbersSurface Gravity: 1 (one kilogram on Earth)Orbital Period: 365.256 daysSatellites: 1 (the Moon)Atmosphere: nitrogen (78%), oxygen (21%), argon, carbon dioxide, neonAverage Temperature: 15° Celsius (77 Kelvin, 59° Fahrenheit)Fast FactIngredients for LifeScientists have gathered enough information about other planets in our solar system to know that none can support life as we know it. Life is not possible without a stable atmosphere containing the right chemical ingredients for living organisms: hydrogen, oxygen, nitrogen, and carbon. These ingredients must be balanced—not too thick or too thin. Life also depends on the presence of water.Jupiter, Saturn, Uranus, and Neptune all have atmospheres made mostly of hydrogen and helium. These planets are called gas giants, because they are mostly made of gas and do not have a solid outer crust.Mercury and Mars have some of the right ingredients, but their atmospheres are far too thin to support life. The atmosphere of Venus is too thick—the planet's surface temperature is more than 460 degrees Celsius (860 degrees Fahrenheit).Jupiter's moon Europa has a thin atmosphere rich with oxygen. It is likely covered by a huge ocean of liquid water. Some astrobiologists think that if life exists elsewhere in the solar system, it will be near vents at the bottom of Europa's ocean.Fast FactEarth to EarthEarth is the only planet in the solar system not named for a Greek or Roman deity. "Earth" originally meant the soil and land of our planet. (This is still what it means when the word is lowercase.) Eventually, Earth came to mean the planet itself.Instructional LinksNASA: SPHERES OF EARTH: An Introduction to Making Observations of Earth Using an Earth System Science ApproachBBC: Journey to the Center of the EarthReferenceEarth and Moon ViewerNational Geographic Science: Planet Earth, earthNASA: Earth Fact SheetWebsiteNASA: Earth ObservatoryCreditsMedia CreditsThe audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.EditorsJeannie Evers, Emdash Editing, Emdash EditingMelissa MacPhee, National Geographic SocietyProducerNational Geographic SocietyotherLast UpdatedOctober 19, 2023User PermissionsFor information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. 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Planet Earth facts and information

Skip to contentNewslettersSubscribeMenuEarthEarth seems to fill the sky in this image taken by the crew of Apollo 17 in 1972. The picture marked the first time astronauts were able to photograph the south polar ice cap.

Photograph courtesy NASASCIENCEREFERENCEPlanet Earth, explainedOur home planet provides us with life and protects us from space.ByMichael Greshko7 min readEarth, our home planet, is a world unlike any other. The third planet from the sun, Earth is the only place in the known universe confirmed to host life.With a radius of 3,959 miles, Earth is the fifth largest planet in our solar system, and it's the only one known for sure to have liquid water on its surface. Earth is also unique in terms of monikers. Every other solar system planet was named for a Greek or Roman deity, but for at least a thousand years, some cultures have described our world using the Germanic word “earth,” which means simply “the ground.”3:17Our dance around the sunEarth orbits the sun once every 365.25 days. Since our calendar years have only 365 days, we add an extra leap day every four years to account for the difference.Though we can't feel it, Earth zooms through its orbit at an average velocity of 18.5 miles a second. During this circuit, our planet is an average of 93 million miles away from the sun, a distance that takes light about eight minutes to traverse. Astronomers define this distance as one astronomical unit (AU), a measure that serves as a handy cosmic yardstick.Earth rotates on its axis every 23.9 hours, defining day and night for surface dwellers. This axis of rotation is tilted 23.4 degrees away from the plane of Earth's orbit around the sun, giving us seasons. Whichever hemisphere is tilted closer to the sun experiences summer, while the hemisphere tilted away gets winter. In the spring and fall, each hemisphere receives similar amounts of light. On two specific dates each year—called the equinoxes—both hemispheres get illuminated equally.Many layers, many featuresAbout 4.5 billion years ago, gravity coaxed Earth to form from the gaseous, dusty disk that surrounded our young sun. Over time, Earth's interior—which is made mostly of silicate rocks and metals—differentiated into four layers.At the planet's heart lies the inner core, a solid sphere of iron and nickel that's 759 miles wide and as hot as 9,800 degrees Fahrenheit. The inner core is surrounded by the outer core, a 1,400-mile-thick band of iron and nickel fluids. Beyond the outer core lies the mantle, a 1,800-mile-thick layer of viscous molten rock on which Earth's outermost layer, the crust, rests. On land, the continental crust is an average of 19 miles thick, but the oceanic crust that forms the seafloor is thinner—about three miles thick—and denser.Like Venus and Mars, Earth has mountains, valleys, and volcanoes. But unlike its rocky siblings, almost 70 percent of Earth's surface is covered in oceans of liquid water that average 2.5 miles deep. These bodies of water contain 97 percent of Earth's volcanoes and the mid-ocean ridge, a massive mountain range more than 40,000 miles long.You May Also LikeSCIENCE4.5 billion years ago, another planet crashed into Earth. We may have found its leftovers.SCIENCEThe moon is even older than we thoughtSCIENCEIs there a 9th planet out there? We may soon find out.Earth's crust and upper mantle are divided into massive plates that grind against each other in slow motion. As these plates collide, tear apart, or slide past each other, they give rise to our very active geology. Earthquakes rumble as these plates snag and slip past each other. Many volcanoes form as seafloor crust smashes into and slides beneath continental crust. When plates of continental crust collide, mountain ranges such as the Himalaya are pushed toward the skies.Protective fields and gasesEarth's atmosphere is 78 percent nitrogen, 21 percent oxygen, and one percent other gases such as carbon dioxide, water vapor, and argon. Much like a greenhouse, this blanket of gases absorbs and retains heat. On average, Earth's surface temperature is about 57 degrees Fahrenheit; without our atmosphere, it'd be zero degrees. In the last two centuries, humans have added enough greenhouse gases to the atmosphere to raise Earth's average temperature by 1.8 degrees Fahrenheit. This extra heat has altered Earth's weather patterns in many ways.The atmosphere not only nourishes life on Earth, but it also protects it: It's thick enough that many meteorites burn up before impact from friction, and its gases—such as ozone—block DNA-damaging ultraviolet light from reaching the surface. But for all that our atmosphere does, it's surprisingly thin. Ninety percent of Earth's atmosphere lies within just 10 miles of the planet's surface.The silhouette of a woman is seen on a Norwegian island beneath the Northern Lights (aurora borealis).

Photograph by Garcia Julien, Getty ImagesWe also enjoy protection from Earth's magnetic field, generated by our planet's rotation and its iron-nickel core. This teardrop-shaped field shields Earth from high-energy particles launched at us from the sun and elsewhere in the cosmos. But due to the field's structure, some particles get funneled to Earth's Poles and collide with our atmosphere, yielding aurorae, the natural fireworks show known by some as the northern lights.Spaceship EarthEarth is the planet we have the best opportunity to understand in detail—helping us see how other rocky planets behave, even those orbiting distant stars. As a result, scientists are increasingly monitoring Earth from space. NASA alone has dozens of missions dedicated to solving our planet's mysteries.At the same time, telescopes are gazing outward to find other Earths. Thanks to instruments such as NASA's Kepler Space Telescope, astronomers have found more than 3,800 planets orbiting other stars, some of which are about the size of Earth, and a handful of which orbit in the zones around their stars that are just the right temperature to be potentially habitable. Other missions, such as the Transiting Exoplanet Survey Satellite, are poised to find even more.SOURCES NASA Science Solar System Exploration - Earth NOAA Ocean Explorer - Mid-Ocean Ridge NOAA Climate - Climate Change NASA - Kepler and K2 Missions IPAC/Caltech - Cool Cosmos NASA Exoplanet ArchiveRelated TopicsEARTHSCIENCE AND TECHNOLOGYSPACESOLAR SYSTEMYou May Also LikeSCIENCEEarth is a geological oddball in our solar system. This is why.SCIENCE9 spectacular night sky events to see in 2024SCIENCEDid Pluto ever actually stop being a planet? Experts debate.SCIENCEHow did life on Earth begin? Here are 3 popular theories.SCIENCE800,000 years ago, a huge meteorite hit Earth. Scientists may have just found where.Go FurtherAnimalsRare gray whale spotted in the Atlantic—and it's only the beginningAnimalsRare gray whale spotted in the Atlantic—and it's only the beginningWhy 'funga' is just as important as flora and faunaScienceWhy 'funga' is just as important as flora and faunaTermite fossils prove mating hasn't changed in 38 million yearsAnimalsTermite fossils prove mating hasn't changed in 38 million yearsPlay to find out which birds dominate at your feeder—and whyAnimalsPlay to find out which birds dominate at your feeder—and whyHow do fireflies get their glow? We finally have some answers.AnimalsHow do fireflies get their glow? We finally have some answers.Bird flu is spreading from pole to pole. Here’s why it matters.AnimalsBird flu is spreading from pole to pole. Here’s why it matters.EnvironmentWhy the 2024 hurricane season could be especially activeEnvironmentWhy the 2024 hurricane season could be especially activeMushroom leather? 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Inside a mysterious sleep conditionScience'Exploding head syndrome'? Inside a mysterious sleep conditionWhat lifting weights does to your body—and your mindScienceMind, Body, WonderWhat lifting weights does to your body—and your mindMushroom leather? The future of fashion is closer than you think.EnvironmentMushroom leather? The future of fashion is closer than you think.Fungi could be the key to major cancer research breakthroughsScienceFungi could be the key to major cancer research breakthroughsWhy 'funga' is just as important as flora and faunaScienceWhy 'funga' is just as important as flora and faunaWhat is a lunar eclipse—and when will the next one happen?ScienceWhat is a lunar eclipse—and when will the next one happen?TravelKingston is making a comeback as culture capital of JamaicaTravelKingston is making a comeback as culture capital of JamaicaYou can watch wild horses roam free in this UK national parkTravelYou can watch wild horses roam free in this UK national parkWhere to stay in Zanzibar, Tanzania's 'spice island'TravelWhere to stay in Zanzibar, Tanzania's 'spice island'To see the real Los Angeles, visit its historic movie theatersTravelTo see the real Los Angeles, visit its historic movie theatersThis comedian went on a quest to find the end of the worldTravelThis comedian went on a quest to find the end of the worldHistory is alive on these European islandsTravelHistory is alive on these European islandsLegalTerms of UsePrivacy PolicyYour US State Privacy RightsChildren's Online Privacy PolicyInterest-Based AdsAbout Nielsen MeasurementDo Not Sell or Share My Personal InformationOur SitesNat Geo HomeAttend a Live EventBook a TripBuy MapsInspire Your KidsShop Nat GeoVisit the D.C. 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Facts About Earth

ExploreSearchSubmitNews & EventsMultimediaNASA+Earth and ClimateExploreClimate ChangeScience in ActionMultimediaDataFor Researchers Explore This SectionEarth and ClimateExploreClimate ChangeScience in ActionMultimediaDataFor Researchers EarthEarth – our home planet – is the third planet from the Sun, and the fifth largest planet. It's the only place we know of inhabited by living things.Quick FactsLength of Day23.9 hoursLength of Year365.25 daysDistance from Sun93,327,712 miles / 150,196,428 kilometersOne Way Light Time to Sun8.350022 minutesWhile Earth is only the fifth largest planet in the solar system, it is the only world in our solar system with liquid water on the surface. Just slightly larger than nearby Venus, Earth is the biggest of the four planets closest to the Sun, all of which are made of rock and metal.Earth is the only planet in the solar system whose English name does not come from Greek or Roman mythology. The name was taken from Old English and Germanic. It simply means "the ground." There are, of course, many names for our planet in the thousands of languages spoken by the people of the third planet from the Sun.

NamesakeThe name Earth is at least 1,000 years old. All of the planets, except for Earth, were named after Greek and Roman gods and goddesses. However, the name Earth is a Germanic word, which simply means “the ground.”Potential for LifeEarth has a very hospitable temperature and mix of chemicals that have made life abundant here. Most notably, Earth is unique in that most of our planet is covered in liquid water, since the temperature allows liquid water to exist for extended periods of time. Earth's vast oceans provided a convenient place for life to begin about 3.8 billion years ago.Some of the features of our planet that make it great for sustaining life are changing due to the ongoing effects of climate change.Size and DistanceWith an equatorial diameter of 7926 miles (12,760 kilometers), Earth is the biggest of the terrestrial planets and the fifth largest planet in our solar system.From an average distance of 93 million miles (150 million kilometers), Earth is exactly one astronomical unit away from the Sun because one astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. This unit provides an easy way to quickly compare planets' distances from the Sun.It takes about eight minutes for light from the Sun to reach our planet.Orbit and RotationAs Earth orbits the Sun, it completes one rotation every 23.9 hours. It takes 365.25 days to complete one trip around the Sun. That extra quarter of a day presents a challenge to our calendar system, which counts one year as 365 days. To keep our yearly calendars consistent with our orbit around the Sun, every four years we add one day. That day is called a leap day, and the year it's added to is called a leap year.Earth's axis of rotation is tilted 23.4 degrees with respect to the plane of Earth's orbit around the Sun. This tilt causes our yearly cycle of seasons. During part of the year, the northern hemisphere is tilted toward the Sun, and the southern hemisphere is tilted away. With the Sun higher in the sky, solar heating is greater in the north producing summer there. Less direct solar heating produces winter in the south. Six months later, the situation is reversed. When spring and fall begin, both hemispheres receive roughly equal amounts of heat from the Sun.MoonsEarth is the only planet that has a single moon. Our Moon is the brightest and most familiar object in the night sky. In many ways, the Moon is responsible for making Earth such a great home. It stabilizes our planet's wobble, which has made the climate less variable over thousands of years.Earth sometimes temporarily hosts orbiting asteroids or large rocks. They are typically trapped by Earth's gravity for a few months or years before returning to an orbit around the Sun. Some asteroids will be in a long “dance” with Earth as both orbit the Sun.Some moons are bits of rock that were captured by a planet's gravity, but our Moon is likely the result of a collision billions of years ago. When Earth was a young planet, a large chunk of rock smashed into it, displacing a portion of Earth's interior. The resulting chunks clumped together and formed our Moon. With a radius of 1,080 miles (1,738 kilometers), the Moon is the fifth largest moon in our solar system (after Ganymede, Titan, Callisto, and Io).The Moon is an average of 238,855 miles (384,400 kilometers) away from Earth. That means 30 Earth-sized planets could fit in between Earth and its Moon.RingsEarth has no rings.FormationWhen the solar system settled into its current layout about 4.5 billion years ago, Earth formed when gravity pulled swirling gas and dust in to become the third planet from the Sun. Like its fellow terrestrial planets, Earth has a central core, a rocky mantle, and a solid crust.StructureEarth is composed of four main layers, starting with an inner core at the planet's center, enveloped by the outer core, mantle, and crust.The inner core is a solid sphere made of iron and nickel metals about 759 miles (1,221 kilometers) in radius. There the temperature is as high as 9,800 degrees Fahrenheit (5,400 degrees Celsius). Surrounding the inner core is the outer core. This layer is about 1,400 miles (2,300 kilometers) thick, made of iron and nickel fluids.In between the outer core and crust is the mantle, the thickest layer. This hot, viscous mixture of molten rock is about 1,800 miles (2,900 kilometers) thick and has the consistency of caramel. The outermost layer, Earth's crust, goes about 19 miles (30 kilometers) deep on average on land. At the bottom of the ocean, the crust is thinner and extends about 3 miles (5 kilometers) from the seafloor to the top of the mantle.SurfaceLike Mars and Venus, Earth has volcanoes, mountains, and valleys. Earth's lithosphere, which includes the crust (both continental and oceanic) and the upper mantle, is divided into huge plates that are constantly moving. For example, the North American plate moves west over the Pacific Ocean basin, roughly at a rate equal to the growth of our fingernails. Earthquakes result when plates grind past one another, ride up over one another, collide to make mountains, or split and separate.Earth's global ocean, which covers nearly 70% of the planet's surface, has an average depth of about 2.5 miles (4 kilometers) and contains 97% of Earth's water. Almost all of Earth's volcanoes are hidden under these oceans. Hawaii's Mauna Kea volcano is taller from base to summit than Mount Everest, but most of it is underwater. Earth's longest mountain range is also underwater, at the bottom of the Arctic and Atlantic oceans. It is four times longer than the Andes, Rockies and Himalayas combined.AtmosphereNear the surface, Earth has an atmosphere that consists of 78% nitrogen, 21% oxygen, and 1% other gases such as argon, carbon dioxide, and neon. The atmosphere affects Earth's long-term climate and short-term local weather and shields us from much of the harmful radiation coming from the Sun. It also protects us from meteoroids, most of which burn up in the atmosphere, seen as meteors in the night sky, before they can strike the surface as meteorites.MagnetosphereOur planet's rapid rotation and molten nickel-iron core give rise to a magnetic field, which the solar wind distorts into a teardrop shape in space. (The solar wind is a stream of charged particles continuously ejected from the Sun.) When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and cause aurorae, or the northern and southern lights.The magnetic field is what causes compass needles to point to the North Pole regardless of which way you turn. But the magnetic polarity of Earth can change, flipping the direction of the magnetic field. The geologic record tells scientists that a magnetic reversal takes place about every 400,000 years on average, but the timing is very irregular. As far as we know, such a magnetic reversal doesn't cause any harm to life on Earth, and a reversal is very unlikely to happen for at least another thousand years. But when it does happen, compass needles are likely to point in many different directions for a few centuries while the switch is being made. And after the switch is completed, they will all point south instead of north.8 Need-to-Know Things About Our Home PlanetMeasuring Up - If the Sun were as tall as a typical front door, Earth would be the size of a nickel.We're On It - Earth is a rocky planet with a solid and dynamic surface of mountains, canyons, plains and more. Most of our planet is covered in water.Breathe Easy - Earth's atmosphere is 78 percent nitrogen, 21 percent oxygen and 1 percent other ingredients—the perfect balance to breathe and live.Our Cosmic Companion - Earth has one moon.Ringless - Earth has no rings.Orbital Science - Many orbiting spacecraft study the Earth from above as a whole system—observing the atmosphere, ocean, glaciers, and the solid earth.Home, Sweet Home - Earth is the perfect place for life as we know it.Protective Shield - Our atmosphere protects us from incoming meteoroids, most of which break up in our atmosphere before they can strike the surface.NASA Space PlaceKid-Friendly EarthOur home planet Earth is a rocky, terrestrial planet. It has a solid and active surface with mountains, valleys, canyons, plains and so much more. Earth is special because it is an ocean planet. Water covers 70% of Earth's surface. Earth's atmosphere is made mostly of nitrogen and has plenty of oxygen for us to breathe. The atmosphere also protects us from incoming meteoroids, most of which break up before they can hit the surface.NASA Space Place: All About EarthKeep ExploringDiscover More Topics From NASAClimate ChangeExplore Earth ScienceEarth Science in ActionOur Solar SystemReturn to topThe National Aeronautics and Space AdministrationNASA explores the unknown in air and space, innovates for the benefit of humanity, and inspires the world through discovery.About NASA's MissionJoin UsHomeNews & EventsMultimediaNASA+MissionsHumans in SpaceEarth & ClimateThe Solar SystemThe UniverseScienceAeronauticsTechnologyLearning ResourcesAbout NASANASA en EspañolFollow NASAMore NASA Social AccountsNASA NewslettersSitemapFor MediaPrivacy PolicyFOIANo FEAR ActOffice of the IGBudget & Annual ReportsAgency Financial ReportsContact NASAAccessibilityPage Editor:SMD Content EditorsResponsible NASA Official for Science:Dana Bolles

Google Earth - Apps on Google Play

le Earth - Apps on Google PlayGamesAppsMoviesBooksKidsgoogle_logo PlayGamesAppsMoviesBooksKidsnonesearchhelp_outline Sign in with Googleplay_appsLibrary & devicespaymentPayments & subscriptionsreviewsMy Play activityredeemOffersPlay PasssettingsSettingsPrivacy Policy • Terms of ServiceGamesAppsMoviesBooksKidsGoogle EarthGoogle LLC4.3star2.95M reviews500M+DownloadsRated for 3+infoInstallShareAdd to wishlistAbout this apparrow_forwardCreate and collaborate on immersive, data-driven maps from anywhere, with the new Google Earth. See the world from above with high-resolution satellite imagery, explore 3D terrain and buildings in hundreds of cities, and dive in to streets and neighborhoods with Street View's 360° perspectives.Updated onJan 31, 2024#7 top free travel & localTravel & LocalData safetyarrow_forwardSafety starts with understanding how developers collect and share your data. Data privacy and security practices may vary based on your use, region, and age. The developer provided this information and may update it over time.No data shared with third partiesLearn more about how developers declare sharingThis app may collect these data typesLocation, Personal info and 6 othersData is encrypted in transitYou can request that data be deletedIndependent security reviewSee detailsRatings and reviewsRatings and reviews are verifiedinfo_outlinearrow_forwardRatings and reviews are verifiedinfo_outlinephone_androidPhonetablet_androidTabletwatchWatchlaptopChromebooktvTVdirections_car_filledCar4.32.69M reviews54321hello 2022more_vert Flag inappropriateFebruary 14, 2024Everything is good but far from user's high expectations on google services. This app works like Google Maps in some way, but you can't use this app for directions ,not like Google maps. and also in both Google map,earth. uses the same pictures which is both sucks in some way, especially when we are checking the city in makati philippines. we can see buildings that are blocking the roads, and some of the pictures are changing directions, so it is very, very confusing.133 people found this review helpfulDid you find this helpful?YesNoCarmelo Anthony Loquiasmore_vert Flag inappropriateShow review historyNovember 8, 2023Hello, this app is very impressive even in 3D even when you load big bridges, towers, buildings etc. But I want to fix something that maybe some people do not appreciate. The fact that the yellow road lanes are above a bridge. Also the fact that I'm using a slow internet is a little disappointing because it is just caused by the internet, but all of the other features and view were amazing. Please fix this issue as soon as possible. That's also why I gave 4 stars.464 people found this review helpfulDid you find this helpful?YesNoCharlz Gian Rosilmore_vert Flag inappropriateSeptember 24, 2021It is a good app, I can discover things in a particular place that I search for,, see the streets, and experience the view of the skyline of the cities or view of a other place,,. But there is something that bugs me alot.... When I press the street view, it will show you a blue line and said tap on the blue line, but once I tap the blue line it take time to load the view and sometimes it just say "no available street view, try tapping the blue line" when I JUST LITERALLY TAP THE BLUE LINE!!!....2,702 people found this review helpfulDid you find this helpful?YesNoSee all reviewsWhat's newThanks for using Google Earth! This release brings a fresh new look, with new features to help you collaborate with others across devices, create maps on the go, and add photos from your camera to your maps.flagFlag as inappropriateApp supportexpand_morepublicWebsiteemailSupport emailapps-help@google.complaceAddress1600 Amphitheatre Parkway, Mountain View 94043shieldPrivacy PolicyMore by Google LLCarrow_forwardYouTube KidsGoogle LLC4.5starGoogle DocsGoogle LLC4.0starGoogle SheetsGoogle LLC4.4starGoogle ClassroomGoogle LLC3.3starGoogle AuthenticatorGoogle LLC4.3starGoogle DriveGoogle LLC4.3starSimilar appsarrow_forwardEarth 3D MapFoxpoi4.4starLive Earth Map - World Map 3DPixamattic Inc -Live Earth Cameras, GPS Navigation4.1starStellarium Mobile - Star MapStellarium Labs4.8starGo Street View Photo SphereFoxpoi3.4starNASANASA 4.6starSolar System ScopeINOVE, s.r.o.4.6starflagFlag as inappropriateGoogle PlayPlay PassPlay PointsGift cardsRedeemRefund policyKids & familyParent GuideFamily sharingTerms of ServicePrivacyAbout Google PlayDevelopersGoogle StorePhilippines (English (United State

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Planet Earth facts and information

Facts About Earth

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