View source for Earth

{{Short description|Third planet from the Sun}}
{{Redirect|Planet Earth|other uses|Earth (disambiguation)|and|Planet Earth (disambiguation)}}
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{{Featured article}}
{{Use American English|date=August 2019}}
{{Use dmy dates|date=September 2022}}
{{Infobox planet
<!---------------------------------------------------------------------------------------
 This infobox has been formatted in the same way as those for other planets and bodies in the Solar System, so please do not change it without discussion on the talk page.
 ---------------------------------------------------------------------------------------->| background = LightSteelBlue
| name = Earth
| alt_names = The world, the [[globe]], [[wikt:Sol III|Sol III]], [[Terra (mythology)|Terra, Tellus]], [[Gaia]], Mother Earth
| adjectives = Earthly, terrestrial, terran, tellurian
| symbol = [[File:Earth symbol (bold).svg|24px|🜨]] and [[File:Globus cruciger (bold).svg|24px|♁]]
| image = The Blue Marble (remastered).jpg
| image_alt = Photograph of Earth taken by the Apollo 17 mission. The Arabian peninsula, Africa and Madagascar lie in the lower half of the disc, whereas Antarctica is at the top.
| caption = ''[[The Blue Marble]]'', [[Apollo 17]], December 1972
| epoch = [[J2000.0|J2000]]<ref group="n" name="epoch" />
| aphelion = {{convert|152,097,597|km|mi|comma=gaps|abbr=on}}
| perihelion = {{convert|147,098,450|km|mi|comma=gaps|abbr=on}}<ref group="n" name="apsis" />
| time_periastron = 2023-Jan-04<ref>{{Cite web|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27399%27&START_TIME=%272023-01-01%27&STOP_TIME=%272023-01-10%27&STEP_SIZE=%271%20hour%27&QUANTITIES=%2720%27&CENTER=%27@Sun%27|title=Horizons Batch Call for 2023 Perihelion|last1=Park|first1=Ryan|date=9 May 2022|publisher=[[NASA]]/[[Jet Propulsion Laboratory|JPL]]|access-date=3 July 2022}}</ref>
| semimajor = {{convert|149,598,023|km|mi|comma=gaps|abbr=on}}<ref name="VSOP87" />
| eccentricity = {{val|0.0167086}}<ref name="VSOP87" />
| period = {{convert|365.256363004|d|yr|comma=gaps|abbr=on|lk=out|disp=x|<ref name="IERS" /><br />(|[[julian year (astronomy)|<sub>j</sub>]])}}
| avg_speed = {{convert|29.7827|km/s|km/h mph|comma=gaps|abbr=on|disp=x|<ref name="earth_fact_sheet" /><br />(|)}}
| mean_anomaly = {{val|358.617|u=°}}
| inclination = {{ublist |{{val|7.155|u=°}} – [[Sun]]'s equator; |{{val|1.57869|u=°}} – [[invariable plane]];<ref name="Allen294" /> |{{val|0.00005|u=°}} – J2000 [[ecliptic]]}}
| asc_node = {{val|-11.26064|u=°}} – J2000 ecliptic<ref name="earth_fact_sheet" />
| arg_peri = {{val|114.20783|u=°}}<ref name="earth_fact_sheet" />
| satellites = 1, the [[Moon]]
| allsatellites = yes
| mean_radius = {{convert|6371.0|km|mi|comma=gaps|abbr=on|disp=x| (|)}}<ref name="hbcp2000" />
| equatorial_radius = {{convert|6378.137|km|mi|comma=gaps|abbr=on|disp=x| (|)}}<ref name=usno /><ref name="WGS-84" />
| polar_radius = {{convert|6356.752|km|mi|comma=gaps|abbr=on|disp=x| (|)}}<ref name="cazenave_ahrens1995" />
| flattening = 1/{{val|298.257222101}} ([[European Terrestrial Reference System 1989|ETRS89]])<ref name="IERS2004" />
| circumference = {{unbulleted list
 | {{convert|40075.017|km|mi|comma=gaps|abbr=on|disp=x|<br />(|), [[equator]]ial}}<ref name="WGS-84">[[World Geodetic System]] (''WGS-84''). [http://earth-info.nga.mil/GandG/wgs84/ Available online] {{Webarchive|url=https://web.archive.org/web/20200311023739/https://earth-info.nga.mil/GandG/wgs84/ |date=11 March 2020}} from [[National Geospatial-Intelligence Agency]].</ref>
 | {{convert|40007.86|km|mi|comma=gaps|abbr=on|disp=x|<br /> (|), [[Meridian (geography)|meridional]]}}<ref name="WGS-84-2" /><ref group="n" name="circ">Earth's [[circumference]] is almost exactly 40,000&nbsp;km because the meter was calibrated on this measurement—more specifically, 1/10-millionth of the distance between the poles and the equator.</ref>
 }}
| surface_area = {{unbulleted list
|{{convert|510,072,000|km2|mi2|comma=gaps|abbr=on||disp=br()}}<ref name="Pidwirny 2006_8" /><ref group="n" name="surfacecover" />
|Land: {{convert|148,940,000|km2|mi2|comma=gaps|abbr=on|disp=br()}}
|Water: {{convert|361,132,000|km2|mi2|comma=gaps|abbr=on|disp=br()}}
}}
| volume = {{val|1.08321|e=12|u=km3}} ({{val|2.59876|e=11|u=cu mi}})<ref name="earth_fact_sheet" />
| mass = {{val|5.972168|e=24|u=kg}} ({{val|1.31668|e=25|u=lb}})<ref name="earthmass" />
| density = {{convert|5.5134|g/cm3|lb/cuin|comma=gaps|abbr=on|disp=br()}}<ref name="earth_fact_sheet" />
| surface_grav = {{convert|9.80665|m/s2|ft/s2|comma=gaps|abbr=on|disp=br()}}<ref name="NIST2008" />
| moment_of_inertia_factor = 0.3307<ref name="Williams1994" />
| escape_velocity = {{convert|11.186|km/s|km/h mph|comma=gaps|abbr=on}}<ref name="earth_fact_sheet" />
| rotation = {{longitem|{{val|1.0|u=d}} <br /> (24h 00&nbsp;m 00s)}}
| sidereal_day = {{longitem|{{val|0.99726968|u=d}}<ref name="Allen296" /> <br /> (23h 56&nbsp;m 4.100s)}}
| rot_velocity = {{convert|1674.4|km/h|km/s km/h mph|order=out|comma=gaps|abbr=on|disp=x|<ref name="Cox2000" /> <br /> (|)}}
| axial_tilt = {{val|23.4392811|u=°}}<ref name="IERS" />
| albedo = {{ublist|class=nowrap |0.367 [[Geometric albedo|geometric]]<ref name="earth_fact_sheet" /> |0.306 [[Bond albedo|Bond]]<ref name="earth_fact_sheet" />}}
| single_temperature = {{cvt|255|K|°C °F|0}}<br />([[Effective temperature|blackbody temperature]])<ref name="American Chemical Society 2013">{{cite web | title=Atmospheres and Planetary Temperatures | website=American Chemical Society | date=2013-07-18 | url=https://www.acs.org/climatescience/energybalance/planetarytemperatures.html | access-date=2023-01-03| archiveurl=https://web.archive.org/web/20230127144936/https://www.acs.org/climatescience/energybalance/planetarytemperatures.html |archivedate=2023-01-27}}</ref>
| atmosphere = yes
| temp_name1 = Celsius{{refn|group=n|Source for minimum,<ref name=asu_lowest_temp /> mean,<ref>{{cite journal |last1=Jones |first1=P. D. |author-link1=Phil Jones (climatologist)|last2=Harpham |first2=C. |title=Estimation of the absolute surface air temperature of the Earth |journal=Journal of Geophysical Research: Atmospheres |date=2013 |volume=118 |issue=8 |pages=3213–3217 |doi=10.1002/jgrd.50359 |bibcode=2013JGRD..118.3213J |language=en |issn=2169-8996 |doi-access=free}}</ref> and maximum<ref name=asu_highest_temp /> surface temperature<!--Moved here to avoid stretching the infobox border-->}}
| min_temp_1 = −89.2 °C
| mean_temp_1 = 14.76 °C
| max_temp_1 = 56.7 °C
| temp_name2 = Fahrenheit
| min_temp_2 = {{not a typo|−128.5 °F}}
| mean_temp_2 = {{not a typo|58.568 °F}}
| max_temp_2 = {{not a typo|134.0 °F}}
| surface_equivalent_dose_rate = {{convert |2.40 |mSv/yr |μSv/h |disp=out}}<ref>{{cite book |author=United Nations Scientific Committee on the Effects of Atomic Radiation |title=Sources and effects of ionizing radiation |date=2008 |publication-date=2010 |publisher=United Nations |location=New York |isbn=978-92-1-142274-0 |url=http://www.unscear.org/unscear/en/publications/2008_1.html |access-date=9 November 2012 |at=Table 1}}</ref>
| abs_magnitude = −3.99
| surface_pressure = {{val|101.325|ul=kPa}} (at sea level)
| atmosphere_composition = {{unbulleted list
 | 78.08% [[nitrogen]] (dry air)
 | 20.95% [[oxygen]] (dry air)
 | ≤1% [[water vapor]] (variable)
 | 0.9340% [[argon]]
 | 0.0415% [[carbon dioxide]]
 | 0.00182% [[neon]]
 | 0.00052% [[helium]]
 | 0.00017% [[methane]]
 | 0.00011% [[krypton]]
 | 0.00006% [[hydrogen]]
}}
Source:<ref name="earth_fact_sheet" />
| note = no
}}'''Earth''' is the third [[planet]] from the [[Sun]] and the only [[astronomical object]] known to [[Planetary habitability|harbor life]]. This is enabled by Earth being a [[Ocean world|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 [[Water distribution on Earth|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 [[Continent|continental]] [[Landmass|landmasses]] within one [[Hemispheres of Earth|hemisphere]], Earth's [[land hemisphere]]. Most of Earth's land is somewhat [[humid]] and covered by vegetation, while large [[Ice sheet|sheets of ice]] at [[Earth's polar regions|Earth's polar]] [[Desert|deserts]] retain more water than Earth's [[groundwater]], lakes, rivers and [[Water vapor#In Earth's atmosphere|atmospheric water]] combined. Earth's crust consists of slowly moving [[Plate tectonics|tectonic plates]], which interact to produce mountain ranges, [[Volcano|volcanoes]], and earthquakes. [[Earth's outer core|Earth has a liquid outer core]] that generates a [[magnetosphere]] capable of deflecting most of the destructive [[Solar wind|solar winds]] and [[cosmic radiation]].

Earth has [[Atmosphere of Earth|a dynamic atmosphere]], which sustains Earth's surface conditions and protects it from most [[Meteoroid|meteoroids]] and [[Ozone layer|UV-light at entry]]. It has a composition of primarily [[nitrogen]] and [[oxygen]]. [[Water vapor]] is widely present in the atmosphere, [[Cloud#Formation|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]] (CO<sub>2</sub>), creates the conditions for both liquid surface water and water vapor to persist via the capturing of [[Solar irradiance|energy from the Sun's light]]. This process maintains the current average surface temperature of 14.76&nbsp;°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 circulation|atmospheric]] and [[Ocean current|ocean currents]], producing a global [[climate system]] with different [[Climate region|climate regions]], and a range of weather phenomena such as [[precipitation]], allowing components such as [[Nitrogen cycle|nitrogen]] to [[Biogeochemical cycle|cycle]].

Earth is [[Hydrostatic equilibrium|rounded]] into [[Earth ellipsoid|an ellipsoid]] with [[Earth's circumference|a circumference]] of about 40,000&nbsp;km. It is the [[List of Solar System objects by size|densest planet in the Solar System]]. Of the four [[Terrestrial planet|rocky planets]], it is the largest and most massive. Earth is about eight [[Light-minute|light-minutes]] away from the Sun and [[Earth's orbit|orbits it]], taking a year (about 365.25 days) to complete one revolution. [[Earth's rotation|Earth rotates]] around its own axis in slightly less than a day (in about 23 hours and 56 minutes). [[Earth#Axial tilt and seasons|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 [[Claimed moons of Earth|permanent]] [[natural satellite]], the [[Moon]], which orbits Earth at 384,400&nbsp;km (1.28 light seconds) and is roughly a quarter as wide as Earth. The Moon's gravity helps stabilize Earth's axis, causes [[Tide|tides]] and [[Tidal acceleration|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, [[Age of Earth|formed 4.5&nbsp;billion years ago]] from gas in the [[Formation and evolution of the Solar System|early Solar System]]. During the first [[billion years]] of [[History of Earth|Earth's history]], the ocean formed and then [[Abiogenesis|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. [[Human|Humans]] emerged [[Human history|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 [[Human impact on the environment|increasingly impacted the planet's environment]]. Humanity's current impact on Earth's climate and biosphere is [[Sustainability|unsustainable]], threatening the livelihood of humans and many other forms of life, and [[Holocene extinction|causing widespread extinctions]].<ref>{{Cite web |title=What Is Climate Change? |url=https://www.un.org/en/climatechange/what-is-climate-change |access-date=17 August 2022 |website=United Nations |language=en}}</ref>

== Etymology ==
The [[Modern English]] word {{anchor|Name|Etymology}} ''Earth'' developed, via [[Middle English]], from an [[Old English]] noun most often spelled ''{{linktext|eorðe}}''.<ref name="oedearth">{{cite book|title=Oxford English Dictionary|edition=3|chapter=earth, ''n.¹''|publisher=[[Oxford University Press]]|place=[[Oxford, England|Oxford]], England|year=2010|isbn=978-0-19-957112-3|doi=10.1093/acref/9780199571123.001.0001}}</ref> It has cognates in every [[Germanic languages|Germanic language]], and their [[proto-Germanic|ancestral root]] has been reconstructed as [[wikt:Appendix:Proto-Germanic/erþō|*''erþō'']]. In its earliest attestation, the word ''eorðe'' was used to translate the many senses of [[Latin language|Latin]] ''{{linktext|terra}}'' and [[Ancient Greek language|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 (goddess)|Terra]]/Tellūs and Greek [[Gaia (goddess)|Gaia]], Earth may have been a [[earth goddess|personified goddess]] in [[Germanic religion (aboriginal)|Germanic paganism]]: late [[Norse mythology]] included [[Jörð]] ("Earth"), a giantess often given as the mother of [[Thor]].<ref>{{cite book|last=Simek|first=Rudolf|author-link=Rudolf Simek|translator-last=Hall|translator-first=Angela|title=Dictionary of Northern Mythology|page=179|publisher=[[Boydell & Brewer|D.S. Brewer]]|year=2007|isbn=978-0-85991-513-7}}</ref>

Historically, "Earth" has been written in lowercase. Beginning with the use of [[Early Middle English]], its [[Definite article|definite sense]] as "the globe" was expressed as "the earth". By the era of [[Early Modern English]], [[Capitalization in English#History of English capitalization|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 [[Solar System|other planets]], though "earth" and forms with "the earth" remain common.<ref name="oedearth" /> [[Style guide|House styles]] now vary: [[Oxford spelling]] recognizes the lowercase form as the most 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?"<ref>{{cite book|title=The New Oxford Dictionary of English|edition=1st|chapter=earth|publisher=Oxford University Press|location=Oxford|year=1998|isbn=978-0-19-861263-6}}</ref>

The name ''Terra'' {{IPAc-en|ˈ|t|ɛr|ə}} occasionally is used in scientific writing and especially in science fiction to distinguish humanity's inhabited planet from others,<ref>{{OED|Terra}}</ref> while in poetry ''Tellus'' {{IPAc-en|ˈ|t|ɛ|l|ə|s}} has been used to denote personification of the Earth.<ref>{{OED|Tellus}}</ref> ''Terra'' is also the name of the planet in some [[Romance languages]], languages that evolved from [[Latin language|Latin]], like Italian and [[Portuguese language|Portuguese]], while in other Romance languages the word gave rise to names with slightly altered spellings, like the [[Spanish language|Spanish]] ''Tierra'' and the [[French language|French]] ''Terre''. The Latinate form ''Gæa'' or ''Gaea'' ({{IPAc-en|lang|'|dʒ|iː|.|ə}}) of the Greek poetic name ''[[Gaia]]'' ({{lang|grc|Γαῖα}}; {{IPA|grc|ɡâi̯.a|lang|link=yes}} or {{IPA-el|ɡâj.ja|}}) is rare, though the alternative spelling ''Gaia'' has become common due to the [[Gaia hypothesis]], in which case its pronunciation is {{IPAc-en|ˈ|g|aɪ|.|ə}} rather than the more classical English {{IPAc-en|ˈ|g|eɪ|.|ə}}.<ref>{{OED|Gaia}}</ref>

There are a number of adjectives for the planet Earth. The word "earthly" is derived from "Earth". From the [[Latin]] ''Terra'' comes ''terran'' {{IPAc-en|ˈ|t|ɛr|ə|n}},<ref>{{OED|Terran}}</ref> ''terrestrial'' {{IPAc-en|t|ə|ˈ|r|ɛ|s|t|r|i|ə|l}},<ref>{{OED|terrestrial}}</ref> and (via French) ''terrene'' {{IPAc-en|t|ə|ˈ|r|iː|n}},<ref>{{OED|terrene}}</ref> and from the Latin ''Tellus'' comes ''tellurian'' {{IPAc-en|t|ɛ|ˈ|l|ʊər|i|ə|n}}<ref>{{OED|tellurian}}</ref> and ''telluric''.<ref>{{Cite encyclopedia |url=http://www.lexico.com/definition/telluric |archive-url=https://web.archive.org/web/20210331100415/https://www.lexico.com/definition/telluric |url-status=dead |archive-date=31 March 2021 |title=telluric |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}}</ref>

== Natural history ==
{{Main|History of Earth|Timeline of natural history}}

=== Formation ===
{{Further|Early Earth|Hadean}}
[[File:The Mysterious Case of the Disappearing Dust.jpg|thumb|upright=1.3|A 2012 artistic impression of the early [[Solar System]]'s [[protoplanetary disk]] from which Earth and other Solar System bodies were formed|center]]

The oldest material found in the [[Solar System]] is dated to {{val|4.5682|0.0002|0.0004}} [[Gigaannum|Ga]] (billion years) ago.<ref name=bouvier_wadhwa2010 /> By {{val|4.54|0.04|u=Ga}} the primordial Earth had formed.<ref name="age_earth1" /> The bodies in [[Formation and evolution of the Solar System|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 [[Cosmic dust|dust]] (including [[primordial nuclide]]s). According to [[nebular theory]], [[planetesimal]]s formed by [[accretion (astrophysics)|accretion]], with the primordial Earth being estimated as likely taking anywhere from 70 to 100 million years to form.<ref>{{cite journal|url=https://ntrs.nasa.gov/citations/20180002991|title=Ag Isotopic Evolution of the Mantle During Accretion: New Constraints from Pd and Ag Metal–Silicate Partitioning|journal=Differentiation: Building the Internal Architecture of Planets|last1=Righter|first1=K.|first2=M.|last2=Schonbachler|date=7 May 2018|volume=2084|page=4034|bibcode=2018LPICo2084.4034R|access-date=25 October 2020}}</ref>

Estimates of the age of the Moon range from 4.5 Ga to significantly younger.<ref>{{Cite journal|last1=Tartèse|first1=Romain|last2=Anand|first2=Mahesh|last3=Gattacceca|first3=Jérôme|last4=Joy|first4=Katherine H.|author-link4=Katherine Joy|last5=Mortimer|first5=James I.|last6=Pernet-Fisher|first6=John F.|last7=Russell|first7=Sara|author7-link=Sara Russell|last8=Snape|first8=Joshua F.|last9=Weiss|first9=Benjamin P.|date=2019|title=Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples|journal=Space Science Reviews|language=en|volume=215|issue=8|page=54|doi=10.1007/s11214-019-0622-x|bibcode=2019SSRv..215...54T|issn=1572-9672|doi-access=free}}</ref> A [[giant impact hypothesis|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 (planet)|Theia]], collided with Earth.<ref name=reilly20091022 /> It hit Earth with a glancing blow and some of its mass merged with Earth.<ref name="canup_asphaug2001b" /><ref>{{cite journal|title=On the origin and composition of Theia: Constraints from new models of the Giant Impact|journal=Icarus|last1=Meier|first1=M. M. M.|last2=Reufer|first2=A.|last3=Wieler|first3=R.|date=4 August 2014|volume=242|page=5|doi=10.1016/j.icarus.2014.08.003|arxiv=1410.3819|bibcode=2014Icar..242..316M|s2cid=119226112}}</ref> Between approximately 4.1 and {{val|3.8|u=Ga}}, numerous [[Impact event|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.<ref>{{cite book|title=Encyclopedia of Astrobiology|first1=Philippe|last1= Claeys|first2=Alessandro|last2=Morbidelli|author-link2=Alessandro Morbidelli (astronomer)|editor-first1=Muriel|editor-last1= Gargaud|editor-first2=Prof Ricardo|editor-last2=Amils|editor-first3= José Cernicharo|editor-last3= Quintanilla|editor-first4= Henderson James (Jim) |editor-last4= Cleaves II|editor-first5=William M.|editor-last5=Irvine|editor-first6= Prof Daniele L.|editor-last6= Pinti|editor-first7= Michel|editor-last7= Viso|year= 2011|publisher=Springer Berlin Heidelberg|pages=909–912|doi=10.1007/978-3-642-11274-4_869|chapter=Late Heavy Bombardment|isbn= 978-3-642-11271-3}}</ref>

=== After formation ===
{{Main|Geological history of Earth}}
[[Atmosphere of Earth|Earth's atmosphere]] and oceans were formed by [[volcanism|volcanic activity]] and [[outgassing]].<ref>{{cite web |url=https://www.lpi.usra.edu/education/timeline/gallery/slide_17.html |title=Earth's Early Atmosphere and Oceans |work=[[Lunar and Planetary Institute]] |publisher=[[Universities Space Research Association]] |access-date=27 June 2019}}</ref> Water vapor from these sources [[Origin of water on Earth|condensed]] into the oceans, augmented by water and ice from asteroids, [[protoplanet]]s, and [[comet]]s.<ref name="watersource" /> Sufficient water to fill the oceans may have been on Earth since it formed.<ref>{{Cite journal|last1=Piani|first1=Laurette|last2=Marrocchi|first2=Yves|last3=Rigaudier|first3=Thomas|last4=Vacher|first4=Lionel G.|last5=Thomassin|first5=Dorian|last6=Marty|first6=Bernard|display-authors=1|date=2020|title=Earth's water may have been inherited from material similar to enstatite chondrite meteorites|url=https://doi.org/10.1126/science.aba1948|journal=Science|language=en|volume=369|issue=6507|pages=1110–1113|doi=10.1126/science.aba1948|issn=0036-8075|pmid=32855337|bibcode=2020Sci...369.1110P|s2cid=221342529}}</ref> In this model, atmospheric [[greenhouse gas]]es kept the oceans from freezing when the newly forming Sun [[Faint young Sun paradox|had only 70%]] of its [[solar luminosity|current luminosity]].<ref name="asp2002" /> By {{val|3.5|u=Ga}}, [[Earth's magnetic field]] was established, which helped prevent the atmosphere from being stripped away by the [[solar wind]].<ref name="physorg20100304" />

[[File:NASA-EarlyEarth-PaleOrangeDot-20190802.jpg|thumb|upright=1.5|''Pale orange dot'', an artist's impression of [[Early Earth]], featuring its tinted orange [[methane]]-rich [[Prebiotic atmosphere|early atmosphere]]<ref name="Trainer Pavlov DeWitt Jimenez pp. 18035–18042">{{cite journal |last1=Trainer |first1=Melissa G. |last2=Pavlov |first2=Alexander A. |last3=DeWitt |first3=H. Langley |last4=Jimenez |first4=Jose L. |last5=McKay |first5=Christopher P. |last6=Toon |first6=Owen B. |last7=Tolbert |first7=Margaret A. |display-authors=1 |date=28 November 2006 |title=Organic haze on Titan and the early Earth |journal=Proceedings of the National Academy of Sciences |volume=103 |issue=48 |pages=18035–18042 |doi=10.1073/pnas.0608561103 |issn=0027-8424 |pmc=1838702 |pmid=17101962 |doi-access=free}}</ref>|center]]

As the molten outer layer of Earth cooled it [[Phase transition|formed]] the first solid [[Earth's crust|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.<ref name="comp">{{cite journal |title=The composition of the Earth |year=1995 |url=https://www.sciencedirect.com/science/article/abs/pii/0009254194001404 |doi=10.1016/0009-2541(94)00140-4 |last1=McDonough |first1=W.F. |last2=Sun |first2=S.-s. |journal=Chemical Geology |volume=120 |issue=3–4 |pages=223–253 |bibcode=1995ChGeo.120..223M }}</ref> The presence of grains of the [[Hadean zircon|mineral zircon of Hadean age]] in [[Eoarchean]] [[sedimentary rock]]s suggests that at least some felsic crust existed as early as {{val|4.4|u=Ga}}, only {{val|140|u=[[Megaannum|Ma]]}} after Earth's formation.<ref name="science310_5756_1947" /> There are two main models of how this initial small volume of continental crust evolved to reach its current abundance:<ref name="williams_santosh2004" /> (1) a relatively steady growth up to the present day,<ref name="science164_1229" /> 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,<ref name="ajes38_613" /><ref name="tp322_19" /> which is supported by isotopic evidence from [[hafnium]] in [[zircon]]s and [[neodymium]] in sedimentary rocks. The two models and the data that support them can be reconciled by large-scale [[crustal recycling|recycling of the continental crust]], particularly during the early stages of Earth's history.<ref name="Dhuime_etal_2018" />

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 [[Geologic time scale|the period]] of hundreds of millions of years, tectonic forces have caused areas of continental crust to group together to form [[supercontinent]]s that have subsequently broken apart. At approximately {{val|750|u=Ma}}, one of the earliest known supercontinents, [[Rodinia]], began to break apart. The continents later recombined to form [[Pannotia]] at {{val|600|–|540|u=Ma}}, then finally [[Pangaea]], which also began to break apart at {{val|180|u=Ma}}.<ref name="bradley_2011" />

The most recent pattern of [[ice age]]s began about {{val|40|u=Ma}},<ref>{{cite news |url=https://www.amnh.org/explore/ology/earth/ask-a-scientist-about-our-environment/how-did-the-ice-age-end |title=When and how did the ice age end? Could another one start? |first=Ro |last=Kinzler |access-date=27 June 2019 |website=Ology|publisher=[[American Museum of Natural History]]}}</ref> and then intensified during the [[Pleistocene]] about {{val|3|u=Ma}}.<ref>{{cite journal |title=Causes of ice age intensification across the Mid-Pleistocene Transition |journal=[[Proc Natl Acad Sci U S A]] |date=12 December 2007 |volume=114 |issue=50 |pages=13114–13119 |doi=10.1073/pnas.1702143114 |pmc=5740680 |pmid=29180424 |first1=Thomas B. |last1=Chalk |first2=Mathis P. |last2=Hain |first3=Gavin L. |last3=Foster |first4=Eelco J. |last4=Rohling |first5=Philip F. |last5=Sexton |first6=Marcus P. S. |last6=Badger |first7=Soraya G. |last7=Cherry |first8=Adam P. |last8=Hasenfratz |first9=Gerald H. |last9=Haug |first10=Samuel L. |last10=Jaccard |first11=Alfredo |last11=Martínez-García |first12=Heiko |last12=Pälike |first13=Richard D. |last13=Pancost |first14=Paul A. |last14=Wilson |display-authors=1|doi-access=free }}</ref> [[High latitude|High-]] and [[middle latitude|middle-latitude]] regions have since undergone repeated cycles of glaciation and thaw, repeating about every 21,000, 41,000 and 100,000 years.<ref name="psc" /> 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.<ref>{{cite journal |url=https://www.sciencedirect.com/science/article/abs/pii/S0277379110003197 |title=The potential of New Zealand kauri (Agathis australis) for testing the synchronicity of abrupt climate change during the Last Glacial Interval (60,000–11,700 years ago) |journal=Quaternary Science Reviews |publisher=Elsevier |last1=Turner |first1=Chris S.M. |display-authors=et al |year=2010 |doi=10.1016/j.quascirev.2010.08.017 |volume=29 |issue=27–28 |pages=3677–3682 |bibcode=2010QSRv...29.3677T |access-date=3 November 2020}}</ref>

=== Origin of life and evolution ===
{{Main|Abiogenesis{{!}}Origin of life|Earliest known life forms|History of life}}
[[Chemical reaction]]s led to the first self-replicating molecules about four billion years ago. A half billion years later, the [[last universal common ancestor|last common ancestor of all current life]] arose.<ref name="sa282_6_90" /> The evolution of [[photosynthesis]] allowed the Sun's energy to be harvested directly by life forms. The resultant [[molecular oxygen]] ({{chem2|O2}}) accumulated in the atmosphere and due to interaction with ultraviolet solar radiation, formed a protective [[ozone layer]] ({{chem2|O3}}) in the upper atmosphere.<ref name="NYT-20131003">{{cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |title=Earth's Oxygen: A Mystery Easy to Take for Granted |url=https://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html |archive-url=https://web.archive.org/web/20131003121909/http://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html |archive-date=3 October 2013 |url-access=limited |date=3 October 2013 |work=[[The New York Times]] |access-date=3 October 2013}}</ref> The incorporation of smaller cells within larger ones resulted in the [[endosymbiotic theory|development of complex cells]] called [[eukaryote]]s.<ref name="jas22_3_225" /> True multicellular organisms formed as cells within [[Colony (biology)|colonies]] became increasingly specialized. Aided by the absorption of harmful [[ultraviolet radiation]] by the ozone layer, life colonized Earth's surface.<ref name="burton20021129" /> Among the earliest [[fossil]] evidence for life is [[microbial mat]] fossils found in 3.48&nbsp;billion-year-old [[sandstone]] in [[Western Australia]],<ref>{{cite journal |last1=Noffke |first1=Nora |author-link=Nora Noffke |last2=Christian |first2=Daniel |last3=Wacey |first3=David |last4=Hazen |first4=Robert M. |author4-link=Robert Hazen |title=Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia |date=8 November 2013 |journal=[[Astrobiology (journal)|Astrobiology]] |doi=10.1089/ast.2013.1030 |bibcode=2013AsBio..13.1103N |pmid=24205812 |pmc=3870916 |volume=13 |issue=12 |pages=1103–1124}}</ref> [[Biogenic substance|biogenic]] [[graphite]] found in 3.7&nbsp;billion-year-old [[metasediment]]ary rocks in [[Western Greenland]],<ref>{{cite journal |last1=Ohtomo |first1=Yoko |last2=Kakegawa |first2=Takeshi |last3=Ishida |first3=Akizumi |last4=Nagase |first4=Toshiro |last5=Rosing |first5=Minik T. |s2cid=54767854 |display-authors=3 |date=January 2014 |title=Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks |journal=[[Nature Geoscience]] |volume=7 |issue=1 |pages=25–28 |bibcode=2014NatGe...7...25O |doi=10.1038/ngeo2025 |issn=1752-0894}}</ref> and remains of [[biotic material]] found in 4.1&nbsp;billion-year-old rocks in Western Australia.<ref>{{cite news |last=Borenstein |first=Seth |title=Hints of life on what was thought to be desolate early Earth |url=http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html |date=19 October 2015 |work=[[Excite (web portal)|Excite]] |location=Yonkers, NY |publisher=[[Mindspark Interactive Network]] |agency=[[Associated Press]] |access-date=20 October 2015 |archive-url=https://web.archive.org/web/20160818063111/https://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html |archive-date=18 August 2016}}</ref><ref>{{cite journal |last1=Bell |first1=Elizabeth A. |last2=Boehnike |first2=Patrick |last3=Harrison |first3=T. Mark |author-link3=T. Mark Harrison |last4=Mao |first4=Wendy L. |author4-link=Wendy Mao |date=19 October 2015 |title=Potentially biogenic carbon preserved in a 4.1&nbsp;billion-year-old zircon |journal=Proc. Natl. Acad. Sci. U.S.A. |doi=10.1073/pnas.1517557112 |issn=1091-6490 |pmid=26483481 |pmc=4664351 |volume=112 |issue=47 |pages=14518–4521 |bibcode=2015PNAS..11214518B |doi-access=free}} Early edition, published online before print.</ref> The [[Earliest known life forms|earliest direct evidence of life]] on Earth is contained in 3.45&nbsp;billion-year-old [[Australia (continent)|Australian]] rocks showing fossils of [[microorganism]]s.<ref>{{cite web |last=Tyrell |first=Kelly April |title=Oldest fossils ever found show life on Earth began before 3.5 billion years ago |url=https://news.wisc.edu/oldest-fossils-ever-found-show-life-on-earth-began-before-3-5-billion-years-ago/ |date=18 December 2017 |publisher=[[University of Wisconsin–Madison]] |access-date=18 December 2017}}</ref><ref>{{cite journal |last1=Schopf |first1=J. William |last2=Kitajima |first2=Kouki |last3=Spicuzza |first3=Michael J. |last4=Kudryavtsev |first4=Anatolly B. |last5=Valley |first5=John W. |title=SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions |year=2017 |journal=[[Proceedings of the National Academy of Sciences of the United States of America|PNAS]] |volume=115 |issue=1 |pages=53–58 |doi=10.1073/pnas.1718063115 |pmid=29255053 |pmc=5776830 |bibcode=2018PNAS..115...53S |doi-access=free}}</ref>[[File:Archean.png|thumb|An artist's impression of the [[Archean]], the [[Geologic time scale#Divisions of geologic time|eon]] after Earth's formation, featuring round [[stromatolite]]s, 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 [[planetary surface|surface]] is marked by [[continent]]s and [[volcano]]es, with the Moon still orbiting Earth half as far as it is today, appearing 2.8 times larger and producing strong [[tide]]s.<ref name="Lunar and Planetary Institute">{{cite web |title=Earth-Moon Dynamics |url=https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/ |access-date=2 September 2022 |website=Lunar and Planetary Institute}}</ref>|center|500x500px]]During the [[Neoproterozoic]], {{val|1000|to|539|u=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.<ref>{{cite book|page=42|title=Climate Change and the Course of Global History|last1=Brooke|first1=John L.|year= 2014|publisher=Cambridge University Press|isbn=978-0-521-87164-8}}</ref><ref>{{cite book|page=56|title=Epigenetic Mechanisms of the Cambrian Explosion|last1=Cabej|first1=Nelson R.|year=2019|publisher=Elsevier Science|isbn=978-0-12-814312-4}}</ref> Following the Cambrian explosion, {{val|535|u=Ma}}, there have been at least five major [[Extinction event|mass extinctions]] and many minor ones.<ref name="Stanley_2016" /> Apart from the proposed current [[Holocene extinction]] event, the [[Cretaceous–Paleogene extinction event|most recent]] was {{val|66|u=Ma}}, when [[Chicxulub impactor|an asteroid impact]] triggered the extinction of the non-avian dinosaurs and other large reptiles, but largely spared small animals such as insects, [[mammal]]s, lizards and birds. Mammalian life has diversified over the past {{val|66|u=Mys}}, and several million years ago an African [[ape]] species gained the ability to stand upright.<ref name="gould1994" />{{better source needed|date=February 2023|reason=Very old source in the context of human evolution, new knowledge of how bipedalism relates to human evolution means this statement may no longer be relevant.}} This facilitated tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which led to the [[Human evolution|evolution of humans]]. The [[History of agriculture|development of agriculture]], and then [[List of ancient civilizations|civilization]], led to humans having an [[Human impact on the environment|influence on Earth]] and the nature and quantity of other life forms that continues to this day.<ref name="bgsa119_1_140" />

=== Future ===
{{Main|Future of Earth}}
{{See also|Global catastrophic risk}}
[[File:Red Giant Earth warm.jpg|thumb|upright=1.3|alt=A dark gray and red sphere representing the Earth lies against a black background to the right of an orange circular object representing the Sun|Conjectured illustration of the scorched Earth after the [[Sun]] has entered the [[red giant]] phase, about 5–7&nbsp;billion years from now]]
Earth's expected long-term future is tied to that of the Sun. Over the next {{val|1.1|u=billion years}}, solar luminosity will increase by 10%, and over the next {{val|3.5|u=billion years}} by 40%.<ref name="sun_future" /> Earth's increasing surface temperature will accelerate the [[carbonate–silicate cycle|inorganic carbon cycle]], reducing {{chem2|CO2}} concentration to levels lethally low for plants ({{val|10|ul=ppm}} for [[C4 carbon fixation|C4 photosynthesis]]) in approximately {{val|100|–|900|u=million years}}.<ref name="britt2000" /><ref name="pnas1_24_9576" /> The lack of vegetation will result in the loss of oxygen in the atmosphere, making animal life impossible.<ref name="ward_brownlee2002" /> Due to the increased luminosity, Earth's mean temperature may reach {{convert|100|C|F|0|abbr=}} in 1.5&nbsp;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&nbsp;billion years.<ref name="Mello-2020">{{Cite journal
|last1=Mello |first1=Fernando de Sousa |last2=Friaça |first2=Amâncio César Santos |date=2020 |title=The end of life on Earth is not the end of the world: converging to an estimate of life span of the biosphere? |journal=International Journal of Astrobiology |language=en |volume=19 |issue=1 |pages=25–42 |doi=10.1017/S1473550419000120 |bibcode=2020IJAsB..19...25D |issn=1473-5504 |doi-access=free}}</ref> Even if the Sun were stable, a fraction of the water in the modern oceans will descend to the [[Mantle (geology)|mantle]], due to reduced steam venting from mid-ocean ridges.<ref name="Mello-2020" /><ref name="hess5_4_569" />

The Sun will [[stellar evolution|evolve]] to become a [[red giant]] in about {{val|5|u=billion years}}. Models predict that the Sun will expand to roughly {{convert|1|AU|e6km e6mi|lk=in|abbr=unit}}, about 250 times its present radius.<ref name="sun_future" /><ref name="sun_future_schroder" /> 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 {{convert|1.7|AU|e6km e6mi|lk=off|abbr=unit}} from the Sun when the star reaches its maximum radius, otherwise, with tidal effects, it may enter the Sun's atmosphere and be vaporized.<ref name="sun_future" />

== Physical characteristics ==
<!--linked from 'Earth physical characteristics tables'-->
{{Further|Geophysics}}

=== Size and shape ===
{{Main|Figure of the Earth}}
{{Further|Earth radius|Earth's circumference|Spherical Earth{{!}}Earth curvature|Geomorphology}}
{{See also|List of highest mountains on Earth}}
[[File:Earth2014shape SouthAmerica small.jpg|thumb|upright=1.3|Earth's western hemisphere showing topography relative to Earth's center instead of to [[mean sea level]], as in common topographic maps]]
[[Figure of the Earth|Earth has a rounded shape]], through [[hydrostatic equilibrium]],<ref name="Horner 2021">{{cite web | last=Horner | first=Jonti | title=I've always wondered: why are the stars, planets and moons round, when comets and asteroids aren't? | website=The Conversation | date=2021-07-16 | url=https://theconversation.com/amp/ive-always-wondered-why-are-the-stars-planets-and-moons-round-when-comets-and-asteroids-arent-160541 | access-date=2023-03-03}}</ref> with an average diameter of {{convert|12742|km|mi|sp=us}}, making it the [[List of Solar System objects by size|fifth largest]] [[Planet#Planetary-mass object|planetary sized]] and largest [[terrestrial planet|terrestrial object]] of the [[Solar System]].<ref>{{Cite web |last=Lea |first=Robert |date=2021-07-06 |title=How big is Earth? |url=https://www.space.com/17638-how-big-is-earth.html |archive-url=https://web.archive.org/web/20240109225632/https://www.space.com/17638-how-big-is-earth.html |archive-date=2024-01-09 |access-date=2024-01-11 |website=Space.com |language=en}}</ref>

Due to [[Earth's rotation]] it has the shape of an [[Earth ellipsoid|ellipsoid]], [[equatorial bulge|bulging at its Equator]]; its diameter is {{convert|43|km|mi|sp=us}} longer there than at its [[Geographical pole|poles]].<ref name="ngdc2006" /><ref name="milbert_smith96" />
Earth's shape furthermore has local [[topography|topographic]] variations. Though the largest local variations, like the [[Mariana Trench]] ({{convert|10925|m|ft|disp=or|abbr=|sp=us}} below local sea level),<ref>{{Cite journal|last1=Stewart|first1=Heather A.|last2=Jamieson|first2=Alan J.|date=2019|title=The five deeps: The location and depth of the deepest place in each of the world's oceans|journal=Earth-Science Reviews|language=en|volume=197|pages=102896|doi=10.1016/j.earscirev.2019.102896|bibcode=2019ESRv..19702896S|issn=0012-8252|doi-access=free}}</ref> only shortens Earth's average radius by 0.17% and [[Mount Everest]] ({{convert|8848|m|ft|disp=or|sp=us}} above local sea level) lengthens it by only 0.14%.{{refn|group=n| 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 plain]]s, would feel smoother.<ref>{{cite web |url=http://billiards.colostate.edu/bd_articles/2013/june13.pdf |title=Is a Pool Ball Smoother than the Earth? |publisher=Billiards Digest |date=1 June 2013 |access-date=26 November 2014}}</ref>}}<ref>{{cite web|url=https://serc.carleton.edu/quantskills/activities/botec_himalayas.html|title=Back-of-the-Envelope Calculations: Scale of the Himalayas|work=[[Carleton University]]|last1=Tewksbury|first1=Barbara|access-date=19 October 2020}}</ref> 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 ({{Convert|6384.4|km|mi|1|abbr=on|disp=or}}) is its farthest point out.<ref name=ps20_5_16 /><ref>{{cite web |url=https://www.npr.org/templates/story/story.php?storyId=9428163 |title=The 'Highest' Spot on Earth |last1=Krulwich|first1=Robert|author-link=Robert Krulwich|work=NPR |date=7 April 2007 |access-date=31 July 2012}}</ref>
Parallel to the rigid land topography [[Ocean surface topography|the Ocean exhibits a more dynamic topography]].<ref>{{Cite web |title=Ocean Surface Topography |url=https://sealevel.jpl.nasa.gov/ocean-observation/ocean-surface-topography |access-date=16 June 2022 |website=Ocean Surface Topography from Space |publisher = NASA |language=en}}</ref>

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.<ref>{{Cite web|title=What is the geoid?|url=https://oceanservice.noaa.gov/facts/geoid.html|access-date=10 October 2020|publisher=[[National Ocean Service]]|language=EN-US}}</ref>

=== Surface ===
{{Further|Planetary surface|Land cover|Land|Pedosphere|Ocean|Sea|Cryosphere|Peplosphere}}
[[File:Global View of the Arctic and Antarctic.jpg|thumb|A [[compositing|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 [[Southern Ocean|Antarctic or Southern Ocean]] and the [[Antarctic ice sheet]] (white) covering [[Antarctica]].]]
[[File:AYool topography 15min.png|thumb|upright=1.3|[[Terrain|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 {{convert|510|e6km2|e6sqmi|0|abbr=unit}}.<ref name="Pidwirny 2006_8" /> Earth can be divided into two [[Hemispheres of Earth|hemispheres]]: by [[latitude]] into the polar [[Northern Hemisphere|Northern]] and [[Southern Hemisphere|Southern]] hemispheres; or by [[longitude]] into the continental [[Eastern Hemisphere|Eastern]] and [[Western Hemisphere|Western]] hemispheres.

Most of Earth's surface is ocean water: 70.8% or {{convert|361|e6km2|e6sqmi|abbr=unit}}.<ref name="Percentage">{{Cite web|url=http://www.physicalgeography.net/fundamentals/8o.html|title=8(o) Introduction to the Oceans|website=www.physicalgeography.net}}</ref> This vast pool of salty water is often called the ''world ocean'',<ref name="Janin Mandia 2012 p. 20">{{cite book |last1=Janin |first1=H. |last2=Mandia |first2=S.A. |title=Rising Sea Levels: An Introduction to Cause and Impact |publisher=McFarland, Incorporated, Publishers |year=2012 |isbn=978-0-7864-5956-8 |url={{GBurl|id=it27LP5V0ugC|p=20}} |access-date=26 August 2022 |page=20}}</ref><ref name="Ro 2020">{{cite web |last=Ro |first=Christine |title=Is It Ocean Or Oceans? |website=Forbes |date=3 February 2020 |url=https://www.forbes.com/sites/christinero/2020/02/03/is-it-ocean-or-oceans/ |access-date=26 August 2022}}</ref> and makes Earth with its dynamic [[hydrosphere]] a water world<ref name="Smith 2021">{{cite web |last=Smith |first=Yvette |title=Earth Is a Water World |website=NASA |date=7 June 2021 |url=http://www.nasa.gov/image-feature/earth-is-a-water-world |access-date=27 August 2022}}</ref><ref name="National Geographic Society 2022">{{cite web |title=Water-Worlds |website=National Geographic Society |date=20 May 2022 |url=https://education.nationalgeographic.org/resource/water-worlds/ |access-date=24 August 2022}}</ref> or [[ocean world]].<ref name="Lunine 2017 pp. 123–130">{{cite journal |last=Lunine |first=Jonathan I. |title=Ocean worlds exploration |journal=Acta Astronautica |publisher=Elsevier BV |volume=131 |year=2017 |issn=0094-5765 |doi=10.1016/j.actaastro.2016.11.017 |pages=123–130|bibcode=2017AcAau.131..123L |doi-access=free }}</ref><ref name="Ocean Worlds">{{cite web |title=Ocean Worlds |website=Ocean Worlds |url=http://www.nasa.gov/specials/ocean-worlds/index.html |access-date=27 August 2022 |archive-date=27 August 2022 |archive-url=https://web.archive.org/web/20220827003111/https://www.nasa.gov/specials/ocean-worlds/index.html |url-status=dead }}</ref> Indeed, in Earth's early history the ocean may have covered Earth completely.<ref name="Voosen p.">{{cite journal | last=Voosen | first=Paul | title=Ancient Earth was a water world | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | date=9 March 2021 | volume=371 | issue=6534 | pages=1088–1089 | issn=0036-8075 | doi=10.1126/science.abh4289 | pmid=33707245 | s2cid=241687784 }}</ref> The world ocean is commonly divided into the Pacific Ocean, Atlantic Ocean, Indian Ocean, [[Southern Ocean|Antarctic or Southern Ocean]], and Arctic Ocean, from largest to smallest. The ocean covers [[oceanic crust|Earth's oceanic crust]], but to a lesser extent with [[shelf sea]]s also [[continental shelf|shelves]] of the [[continental crust]]. The oceanic crust forms large [[oceanic basin]]s with features like [[abyssal plain]]s, [[seamount]]s, [[submarine volcano]]es,<ref name="ngdc2006" /> [[oceanic trench]]es, [[submarine canyon]]s, [[oceanic plateau]]s, and a globe-spanning [[mid-ocean ridge]] system.

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

Earth's land covers 29.2%, or {{convert|149|e6km2|e6sqmi|abbr=unit}} 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 [[landmass]]es, which are (in descending order): [[Afro-Eurasia|Africa-Eurasia]], [[Americas|America (landmass)]], [[Antarctica]], and [[Mainland Australia|Australia (landmass)]].<ref name="DunnMitchell2016">{{cite book|first1=Ross E.|last1=Dunn|first2=Laura J.|last2=Mitchell|first3=Kerry|last3=Ward|title=The New World History: A Field Guide for Teachers and Researchers|url={{GBurl|id=-aowDwAAQBAJ|p=232}}|year=2016|publisher=Univ of California Press|isbn=978-0-520-28989-5|pages=232–}}</ref><ref name="Dempsey 2013">{{cite web |last=Dempsey |first=Caitlin |title=Geography Facts about the World's Continents |website=Geography Realm |date=15 October 2013 |url=https://www.geographyrealm.com/continents/ |access-date=26 August 2022}}</ref><ref name="McColl">{{cite encyclopedia|title=continents|encyclopedia=Encyclopedia of World Geography|volume=1|url={{GBurl|id=DJgnebGbAB8C|p=215}}|editor=R.W. McColl|year=2005|publisher=Facts on File, Inc.|isbn=978-0-8160-7229-3|page=215|access-date=25 August 2022|quote=And since Africa and Asia are connected at the Suez Peninsula, Europe, Africa, and Asia are sometimes combined as Afro-Eurasia or Eurafrasia. The International Olympic Committee's official flag, containing [...] the single continent of America (North and South America being connected as the Isthmus of Panama).}}</ref> These landmasses are further broken down and grouped into the [[continent]]s. The [[terrain]] of the land surface varies greatly and consists of mountains, [[desert]]s, [[plain]]s, [[plateau]]s, and other [[landform]]s. The elevation of the land surface varies from a low point of {{convert|-418|m|ft|abbr=on}} at the [[Dead Sea]], to a maximum altitude of {{convert|8,848|m|ft|abbr=on}} at the top of [[Mount Everest]]. The mean height of land above sea level is about {{convert|797|m|ft|abbr=on}}.<ref>{{cite web|last=Center|first=National Geophysical Data|title=Hypsographic Curve of Earth's Surface from ETOPO1|url=https://ngdc.noaa.gov/mgg/global/etopo1_surface_histogram.html|website=ngdc.noaa.gov|date=19 August 2020 }}</ref>

Land can be [[land cover|covered]] by [[surface water]], snow, ice, artificial structures or vegetation. Most of Earth's land hosts vegetation,<ref name="Carlowicz Simmon 2019">{{cite web | last1=Carlowicz | first1=Michael | last2=Simmon | first2=Robert | title=Seeing Forests for the Trees and the Carbon: Mapping the World's Forests in Three Dimensions | website=NASA Earth Observatory | date=15 July 2019 | url=https://earthobservatory.nasa.gov/features/ForestCarbon#:~:text=They%20cover%20about%2030%20percent,percent%20of%20the%20Earth's%20land. | access-date=31 December 2022}}</ref> but [[ice sheet]]s (10%,<ref name="National Geographic Society 2006">{{cite web | title=Ice Sheet | website=National Geographic Society | date=2006-08-06 | url=https://education.nationalgeographic.org/resource/ice-sheet/ | access-date=2023-01-03}}</ref> not including the equally large land under [[permafrost]])<ref name="Obu 2021 p.">{{cite journal | last=Obu | first=J. | title=How Much of the Earth's Surface is Underlain by Permafrost? | journal=Journal of Geophysical Research: Earth Surface | publisher=American Geophysical Union (AGU) | volume=126 | issue=5 | year=2021 | issn=2169-9003 | doi=10.1029/2021jf006123 | page=| bibcode=2021JGRF..12606123O | s2cid=235532921 }}</ref> or cold as well as hot [[desert]]s (33%)<ref name="Cain 2010">{{cite web | last=Cain | first=Fraser | title=What Percentage of the Earth's Land Surface is Desert? | website=Universe Today | date=2010-06-01 | url=https://www.universetoday.com/65639/what-percentage-of-the-earths-land-surface-is-desert/ | access-date=2023-01-03}}</ref> 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.<ref>{{cite web |title=World Bank arable land |url=http://data.worldbank.org/indicator/AG.LND.ARBL.ZS/countries/1W?display=graph |publisher=World Bank |access-date=19 October 2015}}</ref><ref>{{cite web |title=World Bank permanent cropland |url=http://data.worldbank.org/indicator/AG.LND.CROP.ZS/countries?display=graph |publisher=World Bank |access-date=19 October 2015}}</ref> Earth has an estimated {{convert|16.7|e6km2|e6sqmi|abbr=unit}} of cropland and {{convert|33.5|e6km2|e6sqmi|abbr=unit}} of pastureland.<ref name="Hooke2012">{{cite journal |url=https://www.geosociety.org/gsatoday/archive/22/12/pdf/gt1212.pdf |title=Land transformation by humans: A review |journal=GSA Today |first1=Roger LeB. |last1=Hooke |first2=José F. |last2=Martín-Duque |first3=Javier |last3=Pedraza |volume=22 |issue=12 |pages=4–10 |date=December 2012 |doi=10.1130/GSAT151A.1|bibcode=2012GSAT...12l...4H }}</ref>

The land surface and the [[ocean floor]] form the top of [[Earth's crust]], which together with parts of the [[upper mantle (Earth)|upper mantle]] form [[Lithosphere#Earth's lithosphere|Earth's lithosphere]]. Earth's crust may be divided into [[oceanic crust|oceanic]] and [[continental crust|continental]] crust. Beneath the ocean-floor sediments, the oceanic crust is predominantly [[basalt]]ic, while the continental crust may include lower density materials such as [[granite]], sediments and metamorphic rocks.<ref name="layers_earth" /> Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form about 5% of the mass of the crust.<ref name=jessey />

Earth's surface [[topography]] comprises both the [[ocean surface topography|topography of the ocean surface]], and the [[hypsometry|shape]] of Earth's land surface. The submarine terrain of the ocean floor has an average [[bathymetric]] depth of 4&nbsp;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]].<ref name="kring" /><ref>{{cite book|last=Martin|first=Ronald|url={{GBurl|id=agaOKrvAoeAC}}|title=Earth's Evolving Systems: The History of Planet Earth|publisher=Jones & Bartlett Learning|year=2011|isbn=978-0-7637-8001-2|oclc=635476788}}</ref>

=== Tectonic plates ===
{{Main|Plate tectonics}}
[[File:Tectonic plates (empty).svg|alt=Shows the extent and boundaries of tectonic plates, with superimposed outlines of the continents they support|thumb|[[List of tectonic plates|Earth's major plates]], which are:<ref name="brown_wohletz2005" />{{Hlist|{{Legend inline|#fee6aa|[[Pacific Plate]]}}|{{Legend inline|#fb9a7a|[[African Plate]]<ref group="n" name="jaes41_3_379" />}}|{{Legend inline|#ac8d7f|[[North American Plate]]}}|{{Legend inline|#7fa172|[[Eurasian Plate]]}}|{{Legend inline|#8a9dbe|[[Antarctic Plate]]}}|{{Legend inline|#fcb482|[[Indo-Australian Plate]]}}|{{Legend inline|#ad82b0|[[South American Plate]]}}}}]]

Earth's mechanically rigid outer layer of [[Earth's crust]] and [[upper mantle (Earth)|upper mantle]], the [[lithosphere]], is divided into [[list of tectonic plates|tectonic plates]]. These plates are rigid segments that move relative to each other at one of three boundaries types: at [[convergent boundary|convergent boundaries]], two plates come together; at [[divergent boundary|divergent boundaries]], two plates are pulled apart; and at [[transform fault|transform boundaries]], two plates slide past one another laterally. Along these plate boundaries, earthquakes, [[Volcanism|volcanic activity]], [[Orogeny|mountain-building]], and [[oceanic trench]] formation can occur.<ref name="kious_tilling1999" /> 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.<ref name="seligman2008" />

As the tectonic plates migrate, oceanic crust is [[Subduction|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 {{val|100|u=Myr}} old. The oldest oceanic crust is located in the Western Pacific and is estimated to be {{val|200|u=Myr}} old.<ref name=duennebier1999 /><ref name=noaa20070307 /> By comparison, the oldest dated continental crust is {{val|4030|u=Myr|fmt=commas}},<ref name=cmp134_3 /> although zircons have been found preserved as clasts within Eoarchean sedimentary rocks that give ages up to {{val|4400|u=Myr|fmt=commas}}, indicating that at least some continental crust existed at that time.<ref name=science310_5756_1947 />

The seven major plates are the [[Pacific Plate|Pacific]], [[North American Plate|North American]], [[Eurasian Plate|Eurasian]], [[African Plate|African]], [[Antarctic Plate|Antarctic]], [[Indo-Australian Plate|Indo-Australian]], and [[South American Plate|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 {{val|50|and|55|u=Ma}}. The fastest-moving plates are the oceanic plates, with the [[Cocos Plate]] advancing at a rate of {{convert|75|mm/year|in/year|abbr=on}}<ref name=podp2000 /> and the Pacific Plate moving {{convert|52|–|69|mm/year|in/year|abbr=on}}. At the other extreme, the slowest-moving plate is the South American Plate, progressing at a typical rate of {{convert|10.6|mm/year|in/year|abbr=on}}.<ref name="Argus_etal_2011">{{Cite journal |last1=Argus |first1=D.F. |last2=Gordon |first2=R.G. |last3=DeMets |first3=C. |date=2011 |title=Geologically current motion of 56 plates relative to the no-net-rotation reference frame |journal=Geochemistry, Geophysics, Geosystems |volume=12 |issue=11 |pages=n/a |doi=10.1029/2011GC003751 |bibcode=2011GGG....1211001A |doi-access=free}}</ref>

=== Internal structure ===
{{Main|Internal structure of Earth}}

{| class="wikitable sortable" style="float: right; clear: right; margin-left: 2em; text-align:center;"
|+Geologic layers of Earth<ref name=pnas76_9_4192>{{cite journal |last1=Jordan |first1=T. H. |title=Structural geology of the Earth's interior |journal=Proceedings of the National Academy of Sciences of the United States of America |year=1979 |volume=76 |issue=9 |pages=4192–4200 |doi=10.1073/pnas.76.9.4192 |pmid=16592703 |pmc=411539 |bibcode=1979PNAS...76.4192J|doi-access=free }}</ref>
| colspan="3" style="font-size:smaller; text-align:center;" |[[File:Earth-cutaway-schematic-english.svg|center|frameless]]Illustration of Earth's cutaway, not to scale
|-
!Depth<span style="font-size: smaller;"><ref name=robertson2001>{{cite web |last1=Robertson |first1=Eugene C. |date=26 July 2001 |url=http://pubs.usgs.gov/gip/interior/ |title=The Interior of the Earth |publisher=USGS |access-date=24 March 2007}}</ref><br />(km)</span>
! Component <br />layer name
!Density<br /><span style="font-size: smaller;">(g/cm<sup>3</sup>)</span>
|-
|0–60
| style="text-align:left;" |[[Earth's lithosphere|Lithosphere]]<ref group="n">Locally varies between {{val|5|and|200|u=km}}.</ref>
|—
|-
|0–35
| style="text-align:left;" |[[Earth's crust|Crust]]<ref group="n">Locally varies between {{val|5|and|70|u=km}}.</ref>
|2.2–2.9
|-
|35–660
| style="text-align:left;" |[[Upper mantle (Earth)|Upper mantle]]
|3.4–4.4
|-
|660–2890
| style="text-align:left;" |[[Lower mantle (Earth)|Lower mantle]]
|3.4–5.6
|-
|100–700
| style="text-align:left;" |[[Asthenosphere]]
|—
|-
|2890–5100
| style="text-align:left;" |[[Earth's outer core|Outer core]]
|9.9–12.2
|-
|5100–6378
| style="text-align:left;" |[[Earth's inner core|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 ([[Rheology|rheological]]) properties. The outer layer is a chemically distinct [[Silicate minerals|silicate]] solid crust, which is underlain by a highly [[viscous]] solid mantle. The crust is separated from the mantle by the [[Mohorovičić discontinuity]].<ref name="GeolSoc" /> The thickness of the crust varies from about {{convert|6|km|mi|sp=us}} under the oceans to {{convert|30|-|50|km|mi|abbr=on}} 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.<ref>{{cite news|url=https://education.nationalgeographic.org/resource/lithosphere/|title=Lithosphere|work=[[National Geographic]]|last1=Micalizio|first1=Caryl-Sue|last2=Evers|first2=Jeannie|date=20 May 2015|access-date=13 October 2020}}</ref>

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 {{convert|410|and|660|km|mi|abbr=on}} below the surface, spanning a [[Transition zone (Earth)|transition zone]] that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid [[outer core]] lies above a solid [[Earth's inner core|inner core]].<ref name=tanimoto_ahrens1995 /> 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.<ref name="Deuss_2014" /> The radius of the inner core is about one-fifth of that of Earth.
{{anchor|Density}}Density increases with depth, as described in the table on the right.

Among the Solar System's planetary-sized objects Earth is the [[List of solar system objects by size|object with the highest density]].

=== Chemical composition ===
{{See also|Abundance of elements on Earth}}

[[Earth mass|Earth's mass]] is approximately {{val|5.97|e=24|ul=kg}} (5,970 [[yottagram|Yg]]). It is composed mostly of iron (32.1% [[Mass fraction (chemistry)|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 [[Planetary differentiation#Gravitational separation|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.<ref name="pnas71_12_6973" /><ref name="comp" /> The most common rock constituents of the crust are [[oxide]]s. Over 99% of the [[Earth's crust|crust]] is composed of various oxides of eleven elements, principally oxides containing silicon (the [[silicate mineral]]s), aluminum, iron, calcium, magnesium, potassium, or sodium.<ref name="brown_mussett1981" /><ref name="pnas71_12_6973" />

=== Internal heat ===
{{Main|Earth's internal heat budget}}
[[File:Earth heat flow.jpg|upright=1.3|thumb|A map of [[heat flow]] from Earth's interior to the surface of Earth's crust, mostly along the [[oceanic ridge]]s]]
The major heat-producing [[isotope]]s within Earth are [[potassium-40]], [[uranium-238]], and [[thorium-232]].<ref name=sanders20031210 /> At the center, the temperature may be up to {{convert|6000|C|F}},<ref>{{cite web |title=The Earth's Centre is 1000 Degrees Hotter than Previously Thought |url=http://www.esrf.eu/news/general/Earth-Center-Hotter |website=The European Synchrotron (ESRF) |access-date=12 April 2015 |archive-url=https://web.archive.org/web/20130628075455/http://www.esrf.eu/news/general/Earth-Center-Hotter/Earth-Centre-Hotter/ |archive-date=28 June 2013 |date=25 April 2013 |url-status=dead }}</ref> and the pressure could reach {{convert|360|GPa|e6psi|abbr=unit|lk=on}}.<ref name=ptrsl360_1795_1227 /> 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 {{val|3|ul=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 rock]]s such as [[komatiite]]s that are rarely formed today.<ref name="T&S 137" /><ref name=epsl121_1 />

The mean heat loss from Earth is {{val|87|u=mW m<sup>−2</sup>}}, for a global heat loss of {{val|4.42|e=13|u=W}}.<ref name=jg31_3_267 /> A portion of the core's thermal energy is transported toward the crust by [[mantle plume]]s, a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce [[Hotspot (geology)|hotspots]] and [[flood basalt]]s.<ref name=science246_4926_103 /> More of the heat in Earth is lost through plate tectonics, by mantle upwelling associated with [[mid-ocean ridge]]s. 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.<ref name="heat loss" />

=== Gravitational field ===
{{Main|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 {{convert|9.8|m/s2|abbr=on}}. Local differences in topography, geology, and deeper tectonic structure cause local and broad regional differences in Earth's gravitational field, known as [[Gravity anomaly|gravity anomalies]].<ref>{{cite journal |first1=A. B. |last1=Watts |first2=S. F. |last2=Daly |title=Long wavelength gravity and topography anomalies |journal=Annual Review of Earth and Planetary Sciences |volume=9 |pages=415–418 |date=May 1981 |issue=1 |doi=10.1146/annurev.ea.09.050181.002215 |bibcode=1981AREPS...9..415W}}</ref>

=== Magnetic field ===
{{Main|Earth's magnetic field}}
[[File:Magnetosphere Levels-en.svg|alt=Diagram showing the magnetic field lines of Earth's magnetosphere. The lines are swept back in the anti-solar direction under the influence of the solar wind.|thumb|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 theory|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 {{nowrap|3.05{{e|−5}} [[Tesla (unit)|T]]}}, with a [[magnetic dipole moment]] of {{nowrap|7.79{{e|22}} Am{{sup|2}}}} at epoch 2000, decreasing nearly 6% per century (although it still remains stronger than its long time average).<ref name="dipole">{{cite journal |last1=Olson |first1=Peter |last2=Amit |first2=Hagay |title=Changes in earth's dipole |url=https://pages.jh.edu/~polson1/pdfs/ChangesinEarthsDipole.pdf |journal=Naturwissenschaften |volume=93 |issue=11 |year=2006 |pages=519–542 |doi=10.1007/s00114-006-0138-6 |pmid=16915369 |bibcode=2006NW.....93..519O |s2cid=22283432}}</ref> The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes [[Geomagnetic secular variation|secular variation]] of the main field and [[geomagnetic reversal|field reversals]] at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.<ref name="fitzpatrick2006" /><ref name="campbelwh" />

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.<ref>{{Cite journal|last1=Ganushkina|first1=N. Yu|last2=Liemohn|first2=M. W.|last3=Dubyagin|first3=S.|date=2018|title=Current Systems in the Earth's Magnetosphere|url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017RG000590|journal=Reviews of Geophysics|language=en|volume=56|issue=2|pages=309–332|doi=10.1002/2017RG000590|bibcode=2018RvGeo..56..309G|hdl=2027.42/145256|s2cid=134666611|issn=1944-9208|hdl-access=free|access-date=24 October 2020|archive-date=31 March 2021|archive-url=https://web.archive.org/web/20210331100349/https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017RG000590|url-status=dead}}</ref> 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.<ref>{{cite web |url=http://sci.esa.int/jump.cfm?oid=40994 |title=Cluster reveals the reformation of the Earth's bow shock |publisher=European Space Agency |first=Arnaud |last=Masson |date=11 May 2007 |access-date=16 August 2016}}</ref> [[Charged particle]]s are contained within the magnetosphere; the plasmasphere is defined by low-energy particles that essentially follow magnetic field lines as Earth rotates.<ref>{{cite web |url=http://plasmasphere.nasa.gov/ |title=The Earth's Plasmasphere |publisher=NASA/Marshall Space Flight Center |last=Gallagher |first=Dennis L. |date=14 August 2015 |access-date=16 August 2016}}</ref><ref>{{cite web |url=http://plasmasphere.nasa.gov/formed.html |title=How the Plasmasphere is Formed |publisher=NASA/Marshall Space Flight Center |last=Gallagher |first=Dennis L. |date=27 May 2015 |access-date=16 August 2016 |archive-date=15 November 2016 |archive-url=https://web.archive.org/web/20161115064232/http://plasmasphere.nasa.gov/formed.html |url-status=dead }}</ref> The ring current is defined by medium-energy [[particle]]s that drift relative to the geomagnetic field, but with paths that are still dominated by the magnetic field,<ref name="BaumjohannTreumann1997">{{cite book |title=Basic Space Plasma Physics |publisher=World Scientific |first1=Wolfgang |last1=Baumjohann |first2=Rudolf A. |last2=Treumann |pages=8, 31 |year=1997 |isbn=978-1-86094-079-8}}</ref> and the [[Van Allen radiation belt]]s are formed by high-energy particles whose motion is essentially random, but contained in the magnetosphere.<ref name="Britannica">{{cite encyclopedia |url=https://www.britannica.com/science/ionosphere-and-magnetosphere/Magnetosphere |title=Ionosphere and magnetosphere |encyclopedia=Encyclopædia Britannica |publisher=Encyclopædia Britannica, Inc. |first=Michael B. |last=McElroy |year=2012}}</ref><ref name="Van Allen">{{cite book |title=Origins of Magnetospheric Physics |publisher=University of Iowa Press |last=Van Allen |first=James Alfred |date=2004 |isbn=978-0-87745-921-7 |oclc=646887856}}</ref>

During [[magnetic storm]]s and [[substorm]]s, 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 (astronomy)|aurora]].<ref name="stern2005" />

== Orbit and rotation ==
=== Rotation ===
{{Main|Earth's rotation}}
[[File:EpicEarth-Globespin-tilt-23.4.gif|thumb|upright=1.3|Satellite [[Time-lapse photography|time lapse imagery]] of Earth's rotation showing axis tilt]]
Earth's rotation period relative to the Sun—its mean solar day—is {{nowrap|86,400 seconds}} of mean solar time ({{nowrap|86,400.0025 [[SI]] seconds}}).<ref name="aj136_5_1906" /> Because Earth's solar day is now slightly longer than it was during the 19th century due to [[tidal acceleration|tidal deceleration]], each day varies between {{nowrap|0 and 2 [[millisecond|ms]]}} longer than the mean solar day.<ref name="USNO_TSD" /><ref>{{cite journal |title=Rapid Service/Prediction of Earth Orientation |journal=IERS Bulletin-A |date=9 April 2015 |volume=28 |issue=15 |url=http://maia.usno.navy.mil/ser7/ser7.dat |access-date=12 April 2015 |format=.DAT file (displays as plaintext in browser) |archive-url=https://web.archive.org/web/20150314182157/http://maia.usno.navy.mil/ser7/ser7.dat |archive-date=14 March 2015 |url-status=dead }}</ref>

Earth's rotation period relative to the [[fixed star]]s, called its ''stellar day'' by the [[International Earth Rotation and Reference Systems Service]] (IERS), is {{nowrap|86,164.0989 seconds}} of mean solar time ([[UT1]]), or {{nowrap |23{{smallsup|h}} 56{{smallsup|m}} 4.0989{{smallsup|s}}.}}<ref name="IERS" /><ref group="n" name="Aoki" /> Earth's rotation period relative to the [[precession (astronomy)|precessing]] or moving mean [[March equinox]] (when the Sun is at 90° on the equator)<!-- , misnamed its ''[[sidereal day]]'' [don't know what is this] -->, is {{nowrap|86,164.0905 seconds}} of mean solar time (UT1) {{nowrap|(23{{smallsup|h}} 56{{smallsup|m}} 4.0905{{smallsup|s}})}}.<ref name="IERS" /> Thus the sidereal day is shorter than the stellar day by about 8.4&nbsp;ms.<ref name="seidelmann1992" />

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.<ref name="zeilik1998" /><ref name="angular" />

=== Orbit ===
{{Main|Earth's orbit|Earth's location}}
[[File:Seasons1.svg|thumb|upright=1.3|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 {{convert|150|e6km|e6mi|abbr=unit}}, which is the basis for the [[Astronomical Unit]] and is equal to roughly 8.3 [[light minute]]s or 380 times [[Lunar distance (astronomy)|Earth's distance to the Moon]].

Earth orbits the Sun every 365.2564 mean [[solar day]]s, 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&nbsp;hours. Due to this motion, on average it takes 24&nbsp;hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the [[Meridian (astronomy)|meridian]].

The orbital speed of Earth averages about {{convert|29.78|km/s|km/h mph|abbr=on}}, which is fast enough to travel a distance equal to Earth's diameter, about {{convert|12742|km|mi|abbr=on}}, in seven minutes, and the distance to the Moon, {{convert|384000|km|mi|abbr=on}}, in about 3.5 hours.<ref name="earth_fact_sheet" />

The Moon and Earth orbit a common [[barycenter]] every 27.32&nbsp;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&nbsp;days. Viewed from the [[celestial pole|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 [[axial tilt|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 eclipse]]s and [[solar eclipse]]s.<ref name="earth_fact_sheet" /><ref name="moon_fact_sheet" />

The [[Hill sphere]], or the sphere of [[Gravity|gravitational]] influence, of Earth is about {{convert|1.5|e6km|mi|abbr=unit}} in radius.<ref name="vazquez_etal2006" /><ref group="n" name="hill_radius" /> 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.<ref name="vazquez_etal2006" /> Earth, along with the Solar System, is situated in the [[Milky Way]] and orbits about 28,000&nbsp;[[light-year]]s from its center. It is about 20&nbsp;light-years above the [[galactic plane]] in the [[Orion Arm]].<ref name="nasa20051201" />

=== Axial tilt and seasons ===
{{Main|Axial tilt#Earth}}
[[File:axial tilt vs tropical and polar circles.svg|thumb|upright=1.3|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°<ref name="IERS" /> 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.<ref>{{cite book|last1=Rohli|first1=Robert. V.|title=Climatology|last2=Vega|first2=Anthony J.|publisher=Jones & Bartlett Learning|year=2018|isbn=978-1-284-12656-3|edition=fourth|pages=291–292}}</ref> 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.<ref>{{cite book|last=Burn|first=Chris|title=The Polar Night|url=http://nwtresearch.com/sites/default/files/the-polar-night.pdf|publisher=The Aurora Research Institute|date=March 1996|access-date=28 September 2015}}</ref><ref>{{cite web|url=https://www.antarctica.gov.au/about-antarctica/weather-and-climate/weather/sunlight-hours/|title=Sunlight Hours|work=Australian Antarctic Programme|date=24 June 2020|access-date=13 October 2020}}</ref>

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 [[equinox]]es, 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 [[September equinox|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.<ref name="bromberg2008" />

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&nbsp;years.<ref name="lin2006" /> The orientation (rather than the angle) of Earth's axis also changes over time, [[axial precession|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.<ref name="fisher19960205" />

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.<ref>{{cite web|url=https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/|title=Milankovitch (Orbital) Cycles and Their Role in Earth's Climate|work=NASA|last1=Buis|first1=Alan|date=27 February 2020|access-date=27 October 2020}}</ref><ref group="n" name="solar_energy" /> 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.<ref>{{cite web|url=http://ocp.ldeo.columbia.edu/res/div/ocp/pub/seager/Kang_Seager_subm.pdf|title=Croll Revisited: Why is the Northern Hemisphere Warmer than the Southern Hemisphere?|work=Columbia University|last1=Kang|first1=Sarah M.|last2=Seager|first2=Richard|location=New York|access-date=27 October 2020}}</ref>

== Earth–Moon system ==
{{Further||Satellite system (astronomy)}}

=== Moon ===
{{Main|Moon|Lunar theory|Orbit of the Moon}}
[[File:MarsReconnaissanceOrbiter-Views-EarthMoon-20220422.jpg|thumb|Earth and the Moon as seen from [[Mars]] by the [[Mars Reconnaissance Orbiter]]]]
[[File:Earthrise over Compton crater -LRO full res - edit1.jpg|thumb|View of Earth from the Moon by the [[Lunar Reconnaissance Orbiter]]]]

The Moon is a relatively large, [[Terrestrial planet|terrestrial]], [[Planetary-mass moon|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 (moon)|Charon]] is larger relative to the [[dwarf planet]] [[Pluto]].<ref>{{cite web|url=https://astronomy.com/news/2019/06/whats-so-special-about-our-moon-anyway|title=What's so special about our Moon, anyway?|work=[[Astronomy (magazine)|Astronomy]]|last1=Klemetti|first1=Erik|date=17 June 2019|access-date=13 October 2020}}</ref><ref>{{cite web|url=https://solarsystem.nasa.gov/moons/pluto-moons/charon/in-depth/#:~:text=At%20half%20the%20size%20of,phenomenon%20called%20mutual%20tidal%20locking.|title=Charon|website=NASA|date=19 December 2019|access-date=13 October 2020}}</ref> The natural satellites of other planets are also referred to as "moons", after Earth's.<ref>{{cite web|url=https://theconversation.com/curious-kids-why-is-the-moon-called-the-moon-127899|title=Curious Kids: Why is the moon called the moon?|website=The Conversation|last1=Brown|first1=Toby|date=2 December 2019|access-date=13 October 2020}}</ref> 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.<ref name="canup_asphaug2001b" />

The gravitational attraction between Earth and the Moon causes [[tide]]s on Earth.<ref>{{Cite journal|last1=Coughenour|first1=Christopher L.|last2=Archer|first2=Allen W.|last3=Lacovara|first3=Kenneth J.|author-link3=Kenneth Lacovara|date=2009|title=Tides, tidalites, and secular changes in the Earth–Moon system|url=http://www.sciencedirect.com/science/article/pii/S0012825209001445|journal=Earth-Science Reviews|language=en|volume=97|issue=1|pages=59–79|doi=10.1016/j.earscirev.2009.09.002|bibcode=2009ESRv...97...59C|issn=0012-8252}}</ref> 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.<ref>{{Cite news|last=Kelley|first=Peter|date=17 August 2017|title=Tidally locked exoplanets may be more common than previously thought|url=https://www.washington.edu/news/2017/08/14/tidally-locked-exoplanets-may-be-more-common-than-previously-thought/|access-date=8 October 2020|newspaper=Uw News|language=en}}</ref> As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the [[lunar phase]]s.<ref>{{Cite web|title=Lunar Phases and Eclipses {{!}} Earth's Moon|url=https://solarsystem.nasa.gov/moons/earths-moon/lunar-phases-and-eclipses|access-date=8 October 2020|website=NASA Solar System Exploration}}</ref> Due to their tidal interaction, the Moon recedes from Earth at the rate of approximately {{convert|38|mm/yr|in/yr|abbr=on}}. Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23&nbsp;[[Microsecond|µs]]/yr—add up to significant changes.<ref name="espenak_meeus20070207" /> During the [[Ediacaran]] period, for example, (approximately {{val|620|u=Ma}}) there were 400±7 days in a year, with each day lasting 21.9±0.4 hours.<ref>{{Cite journal |last=Williams |first=G.E. |date=2000 |title=Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit |journal=Reviews of Geophysics |volume=38 |issue=1 |pages=37–59 |doi=10.1029/1999RG900016 |bibcode=2000RvGeo..38...37W |s2cid=51948507|doi-access=free }}</ref>

The Moon may have dramatically affected the development of life by moderating the planet's climate. [[Paleontology|Paleontological]] evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon.<ref name="aaa428_261" /> Some theorists think that without this stabilization against the [[torque]]s 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.<ref>{{cite web|url=https://phys.org/news/2015-01-earth-moon-critical-life.html#:~:text=Lissauer's%20team%20found%20that%20without,day%20angle%20of%2023.5%20degrees.|title=Earth's moon may not be critical to life|work=[[Phys.org]]|last1=Cooper|first1=Keith|date=27 January 2015|access-date=26 October 2020}}</ref><ref>{{cite journal|url=http://web.mit.edu/perron/www/files/Daradich08.pdf|title=Equilibrium rotational stability and figure of Mars|journal=Icarus|last1=Dadarich|first1=Amy|first2=Jerry X.|last2=Mitrovica|author-link2=Jerry X. Mitrovica|first3=Isamu|last3=Matsuyama|first4=J. Taylor|last4=Perron|first5=Michael|last5=Manga|author-link5=Michael Manga|first6=Mark A.|last6=Richards|date=22 November 2007|volume=194|issue=2|pages=463–475|access-date=26 October 2020|doi=10.1016/j.icarus.2007.10.017|archive-date=1 December 2020|archive-url=https://web.archive.org/web/20201201094104/http://web.mit.edu/perron/www/files/Daradich08.pdf|url-status=dead}}</ref>

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.<ref name="angular" /> This allows total and annular solar eclipses to occur on Earth.<ref>{{cite web|url=https://blogs.scientificamerican.com/life-unbounded/the-solar-eclipse-coincidence/|title=The Solar Eclipse Coincidence|work=[[Scientific American]]|last1=Sharf|first1=Caleb A.|date=18 May 2012|access-date=13 October 2020|author1-link=Caleb Scharf}}</ref>

On 1 November 2023, scientists reported that, according to computer simulations, remnants of a [[protoplanet]], named [[Theia (planet)|Theia]], could be inside the Earth, left over from a collision with the Earth in ancient times, and afterwards becoming the [[Moon]].<ref name="NYT-20231101">{{cite news |last=Chang |first=Kenneth |title=A 'Big Whack' Formed the Moon and Left Traces Deep in Earth, a Study Suggests - Two enormous blobs deep inside Earth could be remnants of the birth of the moon. |url=https://www.nytimes.com/2023/11/01/science/moon-formation-theia.html |date=1 November 2023 |work=[[The New York Times]] |url-status=live |archiveurl=https://archive.today/20231101232849/https://www.nytimes.com/2023/11/01/science/moon-formation-theia.html |archivedate=1 November 2023 |accessdate=2 November 2023 }}</ref><ref name="NAT-20231101">{{cite journal |author=Yuan, Qian |display-authors=et al.|title=Moon-forming impactor as a source of Earth's basal mantle anomalies |url=https://www.nature.com/articles/s41586-023-06589-1 |date=1 November 2023 |journal=[[Nature (journal)|Nature]] |volume=623 |issue=7985 |pages=95–99 |doi=10.1038/s41586-023-06589-1 |pmid=37914947 |bibcode=2023Natur.623...95Y |s2cid=264869152 |url-status=live |archiveurl=https://archive.today/20231102061800/https://www.nature.com/articles/s41586-023-06589-1 |archivedate=2 November 2023 |accessdate=2 November 2023 }}</ref>

=== Asteroids and artificial satellites ===
{{Main|Near-Earth object|Claimed moons of Earth}}
[[File:Debris-GEO1280.jpg|thumb|A computer-generated image mapping the prevalence of [[artificial satellite]]s and [[space debris]] around Earth in [[geosynchronous orbit|geosynchronous]] and [[low Earth orbit]]]]
Earth's [[Co-orbital configuration|co-orbital asteroids]] population consists of [[quasi-satellite]]s, objects with a [[horseshoe orbit]] and [[Trojan (celestial body)|trojans]]. There are at least five quasi-satellites, including [[469219 Kamoʻoalewa]].<ref name="christou_asher2011" /><ref>{{cite journal|url=https://academic.oup.com/mnras/article/462/4/3441/2589984|title=Asteroid (469219) 2016 HO3, the smallest and closest Earth quasi-satellite|journal=Monthly Notices of the Royal Astronomical Society|last1=Marcos|first1=C. de la Fuente|last2=Marcos|first2=R. de la Fuente|date=8 August 2016|doi=10.1093/mnras/stw1972|pages=3441–3456|volume=462|issue=4|arxiv=1608.01518|bibcode=2016MNRAS.462.3441D|s2cid=118580771|access-date=28 October 2020}}</ref> A [[Earth trojan|trojan asteroid]] companion, {{mpl|2010 TK|7}}, is [[Libration|librating]] around the leading [[Lagrangian point|Lagrange triangular point]], L4, in [[Earth's orbit]] around the Sun.<ref name="Choi" /> The tiny [[near-Earth asteroid]] {{mpl|2006 RH|120}} makes close approaches to the Earth–Moon system roughly every twenty years. During these approaches, it can orbit Earth for brief periods of time.<ref>{{cite web |title=2006 RH120 ( = 6R10DB9) (A second moon for the Earth?) |url=http://www.birtwhistle.org/Gallery6R10DB9.htm |website=Great Shefford Observatory|access-date=17 July 2015 |archive-url=https://web.archive.org/web/20150206154817/http://www.birtwhistle.org/Gallery6R10DB9.htm |archive-date=6 February 2015}}</ref>

{{As of|2021|9}}, there are 4,550 operational, human-made [[satellite]]s orbiting Earth.<ref name="ucs" /> There are also inoperative satellites, including [[Vanguard 1]], the oldest satellite currently in orbit, and over 16,000 pieces of tracked [[space debris]].<ref group="n" name="space_debris" /> Earth's largest artificial satellite is the [[International Space Station]].<ref>{{Cite book|last1=Welch|first1=Rosanne|url={{GBurl|id=aWGHDwAAQBAJ|q=largest artificial satellite|pg=RA2-PA126}}|title=Technical Innovation in American History: An Encyclopedia of Science and Technology [3 volumes]|last2=Lamphier|first2=Peg A.|year=2019|publisher=ABC-CLIO|isbn=978-1-61069-094-2|page=126|language=en}}</ref>

== Hydrosphere ==
{{Main|Hydrosphere}}
[[File:Ocean world Earth.jpg|thumb|A view of Earth with its [[global ocean]] and [[cloud cover]], which dominate Earth's surface and [[hydrosphere]]; at Earth's [[Polar regions of Earth|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 {{convert|2000|m|ft|abbr=on}}.

The mass of the oceans is approximately 1.35{{e|18}}&nbsp;[[metric ton]]s or about 1/4400 of Earth's total mass. The oceans cover an area of {{convert|361.8|e6km2|e6mi2|abbr=unit}} with a mean depth of {{convert|3682|m|ft|abbr=on}}, resulting in an estimated volume of {{convert|1.332|e9km3|e6cumi|abbr=unit}}.<ref name="ocean23_2_112" /> 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 {{convert|2.7|to|2.8|km|mi|2|abbr=on}}.<ref>{{cite web|title=Third rock from the Sun&nbsp;– restless Earth|url=https://ase.tufts.edu/cosmos/print_chapter.asp?id=4 |access-date=12 April 2015|work=NASA's Cosmos}}</ref> About 97.5% of the water is [[saline water|saline]]; the remaining 2.5% is [[fresh water]].<ref>{{Cite book|title=On Water|url=https://www.eib.org/en/publications/eib-big-ideas-on-water|access-date=7 December 2020|year=2019 |doi=10.2867/509830 |language=en|author1=European Investment Bank|publisher=Publications Office |isbn=9789286143199}}</ref><ref>{{Cite web|title=Chart: Globally, 70% of Freshwater is Used for Agriculture|url=https://blogs.worldbank.org/opendata/chart-globally-70-freshwater-used-agriculture|access-date=7 December 2020|website=World Bank Blogs |date=22 March 2017|last1=Khokhar|first1=Tariq|language=en}}</ref> Most fresh water, about 68.7%, is present as ice in [[ice cap]]s and [[glacier]]s.<ref>{{cite web |last=Perlman |first=Howard|date=17 March 2014|title=The World's Water|url=https://water.usgs.gov/edu/earthwherewater.html|access-date=12 April 2015|work=USGS Water-Science School}}</ref> The remaining 30% is [[ground water]], 1% [[surface water]] (covering only 2.8% of Earth's land)<ref name="Lake Scientist 2016">{{cite web | title=Where Are Lakes? | website=Lake Scientist | date=2016-02-28 | url=https://www.lakescientist.com/where-are-lakes/ | access-date=2023-02-28}}</ref> and other small forms of fresh water deposits such as [[permafrost]], [[water vapor]] in the atmosphere, biological binding, etc. .<ref name="School 2019">{{cite web | last=School | first=Water Science | title=How Much Water is There on Earth? – U.S. Geological Survey | website=USGS.gov | date=2019-11-13 | url=https://www.usgs.gov/special-topics/water-science-school/science/how-much-water-there-earth#science | access-date=2023-03-03}}</ref><ref name="Education 2022">{{cite web | title=Freshwater Resources | website=Education | date=2022-08-18 | url=https://education.nationalgeographic.org/resource/freshwater-resources/ | access-date=2023-02-28}}</ref>

In Earth's coldest regions, snow survives over the summer and [[Ice formation|changes into ice]]. This accumulated snow and ice eventually forms into [[glacier]]s, 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 valley]]s and other landforms.<ref>{{Cite book|last=Hendrix|first=Mark|title=Earth Science: An Introduction|publisher=Cengage|year=2019|isbn=978-0-357-11656-2|location=Boston|page=330}}</ref> [[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.<ref>{{Cite book|last=Hendrix|first=Mark|title=Earth Science: An Introduction |publisher=Cengage |year=2019 |isbn=978-0-357-11656-2|location=Boston|page=329}}</ref>

The average [[salinity]] of Earth's oceans is about 35&nbsp;grams of salt per kilogram of seawater (3.5% salt).<ref name=kennish2001 /> Most of this salt was released from volcanic activity or extracted from cool igneous rocks.<ref name="mullen2002" /> The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms.<ref name="natsci_oxy4" /> Sea water has an important influence on the world's climate, with the oceans acting as a large [[heat reservoir]].<ref name="michon2006" /> Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the [[El Niño–Southern Oscillation]].<ref name="sample2005" />

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.<ref name="Center 2021">{{cite web |last=Center |first=Astrogeology Science |title=Tour of Water in the Solar System – U.S. Geological Survey |website=USGS.gov |date=14 October 2021 |url=https://www.usgs.gov/news/tour-water-solar-system |access-date=19 January 2022}}</ref> Despite some [[Natural satellite|moons]] showing signs of large reservoirs of [[extraterrestrial liquid water]], with possibly even more volume than Earth's ocean, all of them are [[List of largest lakes and seas in the Solar System|large bodies of water]] under a kilometers thick frozen surface layer.<ref>{{cite web |title=Are there oceans on other planets? |website=NOAA's National Ocean Service |date=1 June 2013 |url=https://oceanservice.noaa.gov/facts/et-oceans.html |access-date=19 January 2022}}</ref>

== Atmosphere ==
{{Main|Atmosphere of Earth}}
[[File:ISS-42 Waning sun.jpg|thumb|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 [[Kármán line|altitude of 100&nbsp;km, at the edge of space]]]]
The [[atmospheric pressure]] at Earth's sea level averages {{convert|101.325|kPa|psi|3|abbr=on}},<ref name="Exline2006">{{cite book|last1=Exline|first1=Joseph D. |url=https://www.nasa.gov/pdf/288978main_Meteorology_Guide.pdf|title=Meteorology: An Educator's Resource for Inquiry-Based Learning for Grades 5–9|last2=Levine|first2=Arlene S. |last3=Levine|first3=Joel S.|date=2006|publisher=NASA/Langley Research Center|page=6|id=NP-2006-08-97-LaRC}}</ref> with a [[scale height]] of about {{convert|8.5|km|mi|abbr=on}}.<ref name="earth_fact_sheet" /> 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.<ref name="Exline2006" /> [[Water vapor]] content varies between 0.01% and 4%<ref name="Exline2006" /> but averages about 1%.<ref name="earth_fact_sheet" /> [[Cloud cover|Clouds cover]] around two-thirds of Earth's surface, more so over oceans than land.<ref name="King Platnick Menzel Ackerman 2013 pp. 3826–3852">{{cite journal |last1=King |first1=Michael D. |last2=Platnick |first2=Steven |last3=Menzel |first3=W. Paul |last4=Ackerman |first4=Steven A. |last5=Hubanks |first5=Paul A. |title=Spatial and Temporal Distribution of Clouds Observed by MODIS Onboard the Terra and Aqua Satellites |journal=IEEE Transactions on Geoscience and Remote Sensing |publisher=Institute of Electrical and Electronics Engineers (IEEE) |volume=51 |issue=7 |year=2013 |issn=0196-2892 |doi=10.1109/tgrs.2012.2227333 |pages=3826–3852|bibcode=2013ITGRS..51.3826K |s2cid=206691291 |doi-access=free |hdl=2060/20120010368 |hdl-access=free }}</ref> The height of the [[troposphere]] varies with latitude, ranging between {{convert|8|km|mi|0|abbr=on}} at the poles to {{convert|17|km|mi|0|abbr=on}} at the equator, with some variation resulting from weather and seasonal factors.<ref name="geerts_linacre97" />

Earth's [[biosphere]] has significantly altered its [[Atmosphere of Earth|atmosphere]]. [[Oxygen evolution#Oxygen evolution in nature|Oxygenic photosynthesis]] evolved {{val|2.7|u=Gya}}, [[oxygen catastrophe|forming]] the primarily nitrogen–oxygen atmosphere of today.<ref name="NYT-20131003" /> This change enabled the proliferation of [[aerobic organisms]] and, indirectly, the formation of the ozone layer due to the subsequent [[Ozone–oxygen cycle|conversion of atmospheric {{chem2|O2}} into {{chem2|O3}}]]. The ozone layer blocks [[ultraviolet]] [[solar radiation]], permitting life on land.<ref name="Harrison 2002" /> 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.<ref name="atmosphere" /> 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 {{convert|−18|C|F}}, in contrast to the current {{convert|+15|C|F}},<ref name="Pidwirny2006_7" /> and life on Earth probably would not exist in its current form.<ref name="Narottam2008" />

=== Weather and climate ===
{{Main|Weather|Climate}}
{{Multiple image
| align             = right
| direction         = vertical
| width             = 300
| image1            = IntertropicalConvergenceZone-EO.jpg
| caption1          = The [[ITCZ]]'s band of clouds over the Eastern Pacific and the Americas as seen from space
| image5            = Köppen-Geiger Climate Classification Map (1980–2016) no borders.png
| caption5          = Worldwide [[Köppen climate classification]]s
}}
Earth's atmosphere has no definite boundary, gradually becoming thinner and fading into outer space.<ref>{{cite web|url=https://www.nationalgeographic.com/science/article/where-is-the-edge-of-space-and-what-is-the-karman-line|archive-url=https://web.archive.org/web/20210304132146/https://www.nationalgeographic.com/science/article/where-is-the-edge-of-space-and-what-is-the-karman-line|url-status=dead|archive-date=4 March 2021|title=Where, exactly, is the edge of space? It depends on who you ask|website=[[National Geographic]] |last1=Drake |first1=Nadia |author-link1=Nadia Drake|date=20 December 2018|access-date=4 December 2021}}</ref> Three-quarters of the atmosphere's mass is contained within the first {{convert|11|km|mi|abbr=on}} of the surface; this lowest layer is called the troposphere.<ref>{{cite web|url=https://spaceplace.nasa.gov/troposphere/en/ |title=Troposphere |website=SpacePlace|publisher=[[NASA]]|last1=Erickson|first1=Kristen|last2=Doyle|first2=Heather|date=28 June 2019|access-date=4 December 2021}}</ref> 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.<ref name="moran2005" />

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°.<ref name="berger2002" /> [[Ocean heat content]] and [[Ocean current|currents]] are also important factors in determining climate, particularly the [[thermohaline circulation]] that distributes thermal energy from the equatorial oceans to the polar regions.<ref name=rahmstorf2003 />

Earth receives 1361&nbsp;W/m<sup>2</sup> of&nbsp;[[solar irradiance]].<ref>{{cite web |title=Earth Fact Sheet |website=NASA Space Science Data Coordinated Archive |date=5 June 2023 |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html |access-date=17 September 2023}}</ref><ref>{{cite journal | first1=Odele | last1=Coddington | first2=Judith L. | last2=Lean | author2-link=Judith Lean | first3=Peter | last3=Pilewskie | first4=Martin | last4=Snow | first5=Doug | last5=Lindholm |date=2016 |title=A Solar Irradiance Climate Data Record |journal=Bulletin of the American Meteorological Society |volume=97 |issue=7 |pages=1265–1282 |bibcode=2016BAMS...97.1265C |doi=10.1175/bams-d-14-00265.1 |doi-access=free}}</ref> 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 {{convert|0.4|C-change|F-change|1}} per degree of latitude from the equator.<ref name="sadava_heller2006" /> 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), [[Subtropics|subtropical]], [[temperate]] and [[Polar region|polar]] climates.<ref name="climate_zones" />

Further factors that affect a location's climates are its [[Continentality|proximity to oceans]], the oceanic and atmospheric circulation, and topology.<ref>{{cite book |last1=Rohli |first1=Robert. V.|title=Climatology|last2=Vega|first2=Anthony J.|publisher=Jones & Bartlett Learning|year=2018|isbn=978-1-284-12656-3|edition=fourth|page=49}}</ref> 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.<ref>{{cite book|last1=Rohli|first1=Robert. V.|title=Climatology|last2=Vega|first2=Anthony J.|publisher=Jones & Bartlett Learning |year=2018 |isbn=978-1-284-12656-3|edition=fourth|page=32}}</ref> 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.<ref>{{cite book |last1=Rohli |first1=Robert. V.|title=Climatology|last2=Vega|first2=Anthony J.|publisher=Jones & Bartlett Learning|year=2018|isbn=978-1-284-12656-3|edition=fourth|page=34}}</ref> Finally, temperatures [[Lapse rate|decrease with height]] causing mountainous areas to be colder than low-lying areas.<ref>{{cite book|last1=Rohli|first1=Robert. V. |title=Climatology |last2=Vega |first2=Anthony J. |publisher=Jones & Bartlett Learning |year=2018 |isbn=978-1-284-12656-3 |edition=fourth |page=46}}</ref>

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]].<ref name="moran2005" /> 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.<ref name="hydrologic_cycle" />

The commonly used [[Köppen climate classification]] system has five broad groups ([[tropical climate|humid tropics]], [[arid]], [[humid subtropical climate|humid middle latitudes]], [[Continental climate|continental]] and cold [[polar climate|polar]]), which are further divided into more specific subtypes.<ref name="berger2002" /> The Köppen system rates regions based on observed temperature and precipitation.<ref>{{cite book|last1=Rohli|first1=Robert. V.|title=Climatology|last2=Vega|first2=Anthony J.|publisher=Jones & Bartlett Learning|year=2018|isbn=978-1-284-12656-3|edition=fourth|page=159}}</ref> Surface [[Highest temperature recorded on Earth|air temperature can rise to]] around {{convert|55|C|F}} in [[hot desert]]s, such as [[Death Valley National Park|Death Valley]], and [[Lowest temperature recorded on Earth|can fall as low as]] {{convert|-89|C|F}} in [[Antarctica]].<ref>{{Cite journal | first1=Khalid I. | last1=El Fadli | first2=Randall S. | last2=Cerveny | first3=Christopher C. | last3=Burt | first4=Philip | last4=Eden | first5=David | last5=Parker | first6=Manola | last6=Brunet | first7=Thomas C. | last7=Peterson | first8=Gianpaolo | last8=Mordacchini | first9=Vinicio | last9=Pelino | first10=Pierre | last10=Bessemoulin | first11=José Luis | last11=Stella | first12=Fatima | last12=Driouech | first13=M. M Abdel | last13=Wahab | first14=Matthew B. | last14=Pace |display-authors=1|date=2013|title=World Meteorological Organization Assessment of the Purported World Record 58°C Temperature Extreme at El Azizia, Libya (13 September 1922)|journal=Bulletin of the American Meteorological Society |language=en |volume=94 |issue=2 |pages=199–204 |doi=10.1175/BAMS-D-12-00093.1|bibcode=2013BAMS...94..199E|issn=0003-0007|doi-access=free}}</ref><ref>{{Cite journal|last1=Turner|first1=John|display-authors=et al |date=2009 |title=Record low surface air temperature at Vostok station, Antarctica|journal=Journal of Geophysical Research: Atmospheres |language=en |volume=114 |issue=D24 |page=D24102 |doi=10.1029/2009JD012104|bibcode=2009JGRD..11424102T|issn=2156-2202|doi-access=free}}</ref>

=== Upper atmosphere ===
[[File:Antarctic aurora ESA313457.jpg|thumb|upright=1.3|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 [[Kármán line|edge of space]] at one hundred kilometers and the pink line of [[airglow]] of the lower [[thermosphere]] (invisible), which hosts green and red [[aurora]]e over several hundred kilometers.]]
The upper atmosphere, the atmosphere above the troposphere,<ref>{{cite web |last=Morton |first=Oliver |title=Upper atmosphere Definition und Bedeutung |website=Collins Wörterbuch |date=26 August 2022 |url=https://www.collinsdictionary.com/de/worterbuch/englisch/upper-atmosphere |language=de |access-date=26 August 2022}}</ref> is usually divided into the [[stratosphere]], [[mesosphere]], and [[thermosphere]].<ref name="atmosphere" /> 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.<ref name=sciweek2004 /> 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 {{Convert|100|km|mi|abbr=on}} above Earth's surface, is a working definition for the boundary between the atmosphere and [[outer space]].<ref name=cordoba2004 />

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 [[Atmospheric escape|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.<ref name="jas31_4_1118" /> The leakage of hydrogen into space contributes to the shifting of Earth's atmosphere and surface from an initially [[redox|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.<ref name="sci293_5531_839" /> Hence the ability of hydrogen to escape from the atmosphere may have influenced the nature of life that developed on Earth.<ref name="abedon1997" /> 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.<ref name="arwps4_265" />

== Life on Earth ==
{{Main|Biosphere|History of life}}
[[File:Mollweide Cycle.gif|thumb|upright=1.3|An animation of the changing density of [[primary production|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 [[Planetary habitability|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 [[ecosystem]]s on Earth and has eventually expanded globally forming an overarching biosphere.<ref>{{cite web|url=https://education.nationalgeographic.org/resource/biosphere/ |title=Biosphere |first1=Kim|last1=Rutledge|display-authors=et al|date=24 June 2011|work=National Geographic|access-date=1 November 2020}}</ref> Therefore, life has impacted Earth, significantly altering Earth's atmosphere and surface over long periods of time, causing changes like the [[Great Oxidation Event]].<ref>{{Cite web |title=NASA Astrobiology Institute |url=https://astrobiology.nasa.gov/nai/articles/2019/3/5/clues-of-earths-early-rise-of-oxygen/index.html |access-date=2023-11-09 |website=astrobiology.nasa.gov}}</ref>

Earth's life has over time greatly diversified, allowing the biosphere to have different [[biome]]s, which are inhabited by comparatively similar plants and animals.<ref>{{cite web |url=https://www.bbc.com/bitesize/guides/zmyj6sg/revision/3 |title=Interdependency between animal and plant species |page=3 |work=[[BBC Bitesize]] |publisher=[[BBC]] |access-date=28 June 2019}}</ref> The different biomes developed at distinct elevations or [[Ocean depths|water depths]], planetary temperature [[latitude]]s and on land also with different [[humidity]]. [[Latitudinal gradients in species diversity|Earth's species diversity]] and [[Biomass (ecology)|biomass]] reaches a peak in shallow waters and with [[tropical rainforest|forests, particularly in equatorial, warm and humid conditions]]. While freezing [[Polar regions of Earth|polar regions]] and [[Alpine tundra|high altitudes]], or [[desert|extremely arid areas]] are relatively barren of plant and animal life.<ref name="amnat163_2_192" />

Earth provides liquid water—an environment where complex [[Organic compound|organic molecules]] can assemble and interact, and sufficient energy to sustain a [[metabolism]].<ref name="ab2003" /> Plants and other organisms take up [[nutrient]]s from water, soils and the atmosphere. These nutrients are constantly recycled between different species.<ref>{{Cite book|last1=Singh|first1=J. S.|author-link1=Jamuna Sharan Singh|last2=Singh|first2=S. P.|author-link2=S. P. Singh (biochemist) |last3=Gupta |first3=S.R. |url=https://www.worldcat.org/oclc/896866658|title=Ecology environmental science and conservation|publisher=S. Chand & Company |year=2013 |isbn=978-93-83746-00-2 |edition=First |location=New Delhi|oclc=896866658}}</ref>[[File:Desert_Electric.jpg|thumb|A High Desert storm, sweeps across the Mojave]]

Extreme weather, such as [[tropical cyclone]]s (including [[hurricane]]s and [[typhoon]]s), 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.<ref>{{cite book|title=Oceans and Human Health|first1=Sharon|last1=Smith|author-link=Sharon L. Smith|first2=Lora |last2=Fleming|first3=Helena|last3=Solo-Gabriele|first4=William H.|last4=Gerwick|publisher=Elsevier Science|year= 2011|isbn=978-0-08-087782-2|page=212}}</ref> Many places are subject to earthquakes, [[landslide]]s, [[tsunami]]s, volcanic eruptions, [[tornado]]es, [[blizzard]]s, floods, droughts, [[wildfire]]s, and other calamities and disasters.<ref>{{cite book|title=Natural Disasters|last1=Alexander|first1=David|page=3|year=1993|url={{GBurl|id=wnt0DwAAQBAJ|q=Natural Disasters|pg=PT11}} |publisher=Springer Science & Business Media|isbn=978-1-317-93881-1}}</ref> 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]].<ref>{{cite book|pages=52, 66, 69, 137, 142, 185, 202, 355, 366|title=The Human Impact on the Natural Environment |last1=Goudie |first1=Andrew|author-link1=Andrew Goudie (geographer) |year=2000|publisher=MIT Press|isbn=978-0-262-57138-8}}</ref> Human activities release greenhouse gases into the atmosphere which cause [[global warming]].<ref name=ConsensusOnConsensus>{{Cite journal | first1=John | last1=Cook | first2=Naomi | last2=Oreskes | author2-link=Naomi Oreskes | first3=Peter T. | last3=Doran | author3-link=Peter Doran | first4=William R. L. | last4=Anderegg | first5=Bart | last5=Verheggen | first6=Ed W | last6=Maibach | author6-link=Edward Maibach | first7=J. Stuart | last7=Carlton | first8=Stephan | last8=Lewandowsky | author8-link=Stephan Lewandowsky | first9=Andrew G. | last9=Skuce | first10=Sarah A. | last10=Green | first11=Dana | last11=Nuccitelli | first12=Peter | last12=Jacobs | first13=Mark | last13=Richardson | first14=Bärbel | last14=Winkler | first15=Rob | last15=Painting | first16=Ken | last16=Rice | date=2016 |title=Consensus on consensus: a synthesis of consensus estimates on human-caused global warming|journal=Environmental Research Letters |language=en |volume=11 |issue=4 |page=048002 |doi=10.1088/1748-9326/11/4/048002 |bibcode=2016ERL....11d8002C |issn=1748-9326|doi-access=free| hdl=1983/34949783-dac1-4ce7-ad95-5dc0798930a6 | hdl-access=free }}</ref> This is driving [[Effects of climate change|changes]] such as the [[Retreat of glaciers since 1850|melting of glaciers and ice sheets]], a [[Sea level rise|global rise in average sea levels]], increased risk of drought and wildfires, and migration of species to colder areas.<ref name="Global Warming Effects">{{Cite web|date=14 January 2019|title=Global Warming Effects|url=https://www.nationalgeographic.com/environment/global-warming/global-warming-effects/|archive-url=https://web.archive.org/web/20170118014716/http://www.nationalgeographic.com/environment/global-warming/global-warming-effects/|url-status=dead|archive-date=18 January 2017|access-date=16 September 2020|website=National Geographic|language=en}}</ref>


== Human geography ==
{{Main|Human geography}}
{{See also|World}}
[[File:Earth's City Lights by DMSP, 1994-1995 (large).jpg|thumb|upright=1.3|A composite image of [[light pollution|artificial light emissions]] at night on a map of Earth]]
Originating from earlier [[primate]]s in Eastern Africa 300,000 years ago [[History of human migration|humans have since been migrating]] and with the advent of agriculture in the 10th millennium BC increasingly [[Sedentism|settling]] Earth's land.<ref>{{Cite web |title=Introduction to Human Evolution {{!}} The Smithsonian Institution's Human Origins Program |url=http://humanorigins.si.edu/education/introduction-human-evolution |access-date=2023-11-09 |website=humanorigins.si.edu |date=11 July 2022 |language=en}}</ref> In the 20th century [[Antarctica]] had been the last continent to see a first and until today limited human presence.

[[World population|Human population]] has since the 19th century grown exponentially to seven billion in the early 2010s,<ref>{{cite web |url=https://news.yahoo.com/various-7-billionth-babies-celebrated-worldwide-064439018.html |title=Various '7 billionth' babies celebrated worldwide |date=31 October 2011|agency=Associated Press|access-date=31 October 2011 |url-status=dead |archive-url=https://web.archive.org/web/20111031182613/http://news.yahoo.com/various-7-billionth-babies-celebrated-worldwide-064439018.html |work=Yahoo News |last1=Gomez |first1=Jim |last2=Sullivan|first2=Tim|archive-date=31 October 2011}}</ref> and is projected to peak at around ten billion in the second half of the 21st century.<ref name="Harvey-2020">{{Cite news |last=Harvey |first=Fiona |date=15 July 2020 |title=World population in 2100 could be 2 billion below UN forecasts, study suggests |language=en-GB |work=The Guardian |url=https://www.theguardian.com/world/2020/jul/15/world-population-in-2100-could-be-2-billion-below-un-forecasts-study-suggests |url-access=registration |access-date=18 September 2020 |issn=0261-3077}}</ref> Most of the growth is expected to take place in [[sub-Saharan Africa]].<ref name="Harvey-2020" />

Distribution and [[Population density#Human population density|density of human population]] varies greatly around the world with the majority living in south to eastern Asia and 90% inhabiting only the [[Northern Hemisphere]] of Earth,<ref>{{Cite web |url=https://www.businessinsider.com/90-of-people-live-in-the-northern-hemisphere-2012-5 |title=MAP OF THE DAY: Pretty Much Everyone Lives In The Northern Hemisphere |date=4 May 2012 |work=Business Insider|last1=Lutz|first1=Ashley|access-date=5 January 2019}}</ref> partly due to the [[Land hemisphere|hemispherical predominance of the world's land mass]], with 68% of the world's land mass being in the Northern Hemisphere.<ref>{{Cite web |url=http://phl.upr.edu/library/notes/distributionoflandmassesofthepaleo-earth |title=Distribution of landmasses of the Paleo-Earth |first1=Abel |last1=Méndez |author-link1=Abel Méndez |date=6 July 2011 |publisher=University of Puerto Rico at Arecibo |access-date=5 January 2019 |archive-date=6 January 2019 |archive-url=https://web.archive.org/web/20190106010959/http://phl.upr.edu/library/notes/distributionoflandmassesofthepaleo-earth |url-status=dead }}</ref> Furthermore, since the 19th century humans have increasingly converged into urban areas with the majority living in urban areas by the 21st century.<ref name="OWID_urbanization_2019" />

Beyond Earth's surface humans have lived on a temporary basis, with only special purpose deep [[underground living|underground]] and [[underwater living|underwater]] presence, and a few [[space station]]s. Human population virtually completely remains on Earth's surface, fully depending on Earth and the environment it sustains. Since the second half of the 20th century, some hundreds of humans have temporarily stayed beyond Earth, a tiny fraction of whom have reached another celestial body, the Moon.<ref name="shayler_vis2005" /><ref>{{Cite news|last=Holmes|first=Oliver|date=19 November 2018 |title=Space: how far have we gone – and where are we going?|language=en-GB|work=The Guardian|url=https://www.theguardian.com/science/2018/nov/19/space-how-far-have-we-gone-and-where-are-we-going|access-date=10 October 2020|issn=0261-3077}}</ref>

Earth has been subject to extensive human settlement, and humans have developed diverse societies and cultures. Most of Earth's land has been territorially claimed since the 19th century by [[sovereign state]]s (countries) separated by [[Border|political borders]], and [[List of sovereign states|205 such states]] exist today,<ref>{{cite web | title = Member States <nowiki>|</nowiki> United Nations | url = https://www.un.org/en/about-us/member-states | publisher = United Nations | access-date = 2024-01-03 | archive-url = https://web.archive.org/web/20230301201032/https://www.un.org/en/about-us/member-states | archive-date = 2023-03-01 | url-status=live}}</ref> with only parts of Antarctica and a few small regions [[Terra nullius|remaining unclaimed]].<ref>{{cite book|last1=Lloyd|first1=John|author-link1=John Lloyd (producer)|title=The Discretely Plumper Second QI Book of General Ignorance|last2=Mitchinson|first2=John|author-link2=John Mitchinson (researcher)|publisher=Faber & Faber |year=2010|isbn=978-0-571-29072-7|pages=116–117}}</ref> Most of these states together form the United Nations, the leading worldwide [[intergovernmental organization]],<ref>{{cite book|last1=Smith|first1=Courtney B.|url=https://www.rienner.com/uploads/47d958f8700e6.pdf|title=Politics and Process at the United Nations: The Global Dance|publisher=Lynne Reiner|year=2006|isbn=978-1-58826-323-0|pages=1–4}}</ref> which extends human governance [[Law of the Sea|over the ocean]] and [[Antarctic Treaty System|Antarctica]], and therefore all of Earth.

=== Natural resources and land use ===
{{Main|Natural resource|Land use}}
[[File:Global-land-use-graphic.png|thumb|upright=1.3|Earth's land use for human agriculture]]
Earth has resources that have been exploited by humans.<ref>{{cite news|title=What are the consequences of the overexploitation of natural resources?|work=[[Iberdrola]] |url=https://www.iberdrola.com/environment/overexploitation-of-natural-resources|access-date=28 June 2019}}</ref> Those termed [[non-renewable resource]]s, such as [[fossil fuel]]s, are only replenished over geological timescales.<ref>{{cite journal|date=20 April 2016|title=13. Exploitation of Natural Resources|url=https://www.eea.europa.eu/publications/92-826-5409-5/page013new.html|journal=[[European Environment Agency]]|publisher=[[European Union]]|access-date=28 June 2019}}</ref> Large deposits of fossil fuels are obtained from Earth's crust, consisting of coal, petroleum, and natural gas.<ref>{{cite news|last=Huebsch|first=Russell|date=29 September 2017|title=How Are Fossil Fuels Extracted From the Ground?|work=Sciencing|publisher=[[Leaf Group]] Media|url=https://sciencing.com/how-are-fossil-fuels-extracted-from-the-ground-12227026.html |access-date=28 June 2019}}</ref> These deposits are used by humans both for energy production and as feedstock for chemical production.<ref>{{cite web |title=Electricity generation – what are the options?|url=http://www.world-nuclear.org/nuclear-basics/electricity-generation-what-are-the-options.aspx|access-date=28 June 2019 |work=[[World Nuclear Association]]}}</ref> Mineral [[ore]] bodies have also been formed within the crust through a process of [[ore genesis]], resulting from actions of [[magmatism]], erosion, and plate tectonics.<ref>{{cite journal|last1=Brimhall|first1=George|date=May 1991|title=The Genesis of Ores|url=https://www.jstor.org/stable/24936905 |journal=Scientific American |publisher=Nature America|volume=264|pages=84–91|doi=10.1038/scientificamerican0591-84|jstor=24936905|access-date=13 October 2020 |number=5 |bibcode=1991SciAm.264e..84B}}</ref> These metals and other elements are extracted by mining, a process which often brings environmental and health damage.<ref>{{Cite book|last=Lunine|first=Jonathan I. |author-link=Jonathan Lunine|title=Earth: Evolution of a Habitable World|publisher=Cambridge University Press |year=2013 |isbn=978-0-521-61519-8 |edition=second|pages=292–294}}</ref>

Earth's biosphere produces many useful biological products for humans, including food, wood, [[pharmaceutical]]s, oxygen, and the recycling of organic waste. The land-based ecosystem depends upon [[topsoil]] and fresh water, and the oceanic ecosystem depends on dissolved nutrients washed down from the land.<ref name="science299_5607_673" /> In 2019, {{convert|39|e6km2|e6sqmi|abbr=unit}} of Earth's land surface consisted of forest and woodlands, {{convert|12|e6km2|e6sqmi|abbr=unit}} was shrub and grassland, {{convert|40|e6km2|e6sqmi|abbr=unit}} were used for animal feed production and grazing, and {{convert|11|e6km2|e6sqmi|abbr=unit}} were cultivated as croplands.<ref name="OWID_2019" /> Of the 12{{En dash}}14% of ice-free land that is used for croplands, 2 [[percentage point]]s were irrigated in 2015.<ref>{{Cite book |author=IPCC |title=IPCC Special Report on Climate Change and Land |year=2019 |page=8 |chapter=Summary for Policymakers |author-link=IPCC <!-- |display-authors= 4 --> |chapter-url=https://www.ipcc.ch/site/assets/uploads/sites/4/2019/12/02_Summary-for-Policymakers_SPM.pdf}}</ref> Humans use [[building material]]s to construct shelters.<ref>{{cite book |last1=Tate|first1=Nikki|author-link=Nikki Tate|title=Take Shelter: At Home Around the World|last2=Tate-Stratton|first2=Dani|year=2014|publisher=Orca Book Publishers|isbn=978-1-4598-0742-6|page=6}}</ref>

=== Humans and the environment ===
{{Main|Human impact on the environment|Climate change}}
[[File:Global Temperature And Forces With Fahrenheit.svg|alt=The graph from 1880 to 2020 shows natural drivers exhibiting fluctuations of about 0.3 degrees Celsius. Human drivers steadily increase by 0.3 degrees over 100 years to 1980, then steeply by 0.8 degrees more over the past 40 years.|thumb|upright=1.3|Change in average surface air temperature and drivers for that change. Human activity has caused increased temperatures, with natural forces adding some variability.<ref>{{Cite book |author=IPCC |author-link=IPCC |year=2021 |title=Climate Change 2021: The Physical Science Basis |series=Contribution of Working Group I to the [[IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change |display-editors=4 |editor1-first=V. |editor1-last=Masson-Delmotte |editor2-first=P. |editor2-last=Zhai |editor3-first=A. |editor3-last=Pirani |editor4-first=S. L. |editor4-last=Connors |editor5-first=C. |editor5-last=Péan |editor6-first=S. |editor6-last=Berger |editor7-first=N. |editor7-last=Cau |editor8-first=Y. |editor8-last=Chen |editor9-first=L. |editor9-last=Goldfarb |editor10-first=M. I. |editor10-last=Gomis |publisher=Cambridge University Press (In Press) |place=Cambridge, United Kingdom and New York, NY, US |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf |at=SPM-7}}</ref>]]

Human activities have impacted Earth's environments. Through activities such as the burning of fossil fuels, humans have been increasing the amount of [[greenhouse gas]]es in the atmosphere, altering [[Earth's energy budget]] and climate.<ref name=ConsensusOnConsensus /><ref>{{Cite web |url=https://earthobservatory.nasa.gov/features/EnergyBalance |title=Climate and Earth's Energy Budget |first1=Rebecca|last1=Lindsey |date=14 January 2009 |website=Earth Observatory|publisher=[[NASA]]|language=en |access-date=19 December 2021}}</ref> It is estimated that global temperatures in the year 2020 were {{convert|1.2|C-change}} warmer than the preindustrial baseline.<ref>{{cite web|date=14 January 2021|title=The State of the Global Climate 2020|url=https://public-old.wmo.int/en/our-mandate/climate/wmo-statement-state-of-global-climate|archive-url=https://web.archive.org/web/20231129232510/https://public-old.wmo.int/en/our-mandate/climate/wmo-statement-state-of-global-climate|url-status=dead|archive-date=29 November 2023|access-date=3 March 2021|website=World Meteorological Organization |language=en}}</ref> This increase in temperature, known as [[global warming]], has contributed to the [[Retreat of glaciers since 1850|melting of glaciers]], [[Sea level rise|rising sea levels]], increased risk of drought and wildfires, and migration of species to colder areas.<ref name="Global Warming Effects" />

The concept of [[planetary boundaries]] was introduced to quantify humanity's impact on Earth. Of the nine identified boundaries, five have been crossed: [[Biodiversity loss|Biosphere integrity]], climate change, chemical pollution, destruction of wild habitats and the [[nitrogen cycle]] are thought to have passed the safe threshold.<ref name="Boundaries">{{cite web |title=We've crossed four of nine planetary boundaries. What does this mean? |website=[[Mongabay]] |last1=DiGirolamo |first1=Mike |date=8 September 2021 |url=https://news.mongabay.com/2021/09/weve-crossed-four-of-nine-planetary-boundaries-what-does-this-mean/ |access-date=27 January 2022}}</ref><ref>{{cite news |last1=Carrington |first1=Damien |title=Chemical pollution has passed safe limit for humanity, say scientists |url=https://www.theguardian.com/environment/2022/jan/18/chemical-pollution-has-passed-safe-limit-for-humanity-say-scientists |work=The Guardian |date=18 January 2022 |language=en}}</ref> As of 2018, no country meets the basic needs of its population without transgressing planetary boundaries. It is thought possible to provide all basic physical needs globally within sustainable levels of resource use.<ref>{{Cite journal|last1=O'Neill|first1=Daniel W.|last2=Fanning|first2=Andrew L.|last3=Lamb|first3=William F.|last4=Steinberger|first4=Julia K.|author4-link=Julia Steinberger|date=2018|title=A good life for all within planetary boundaries|url=https://www.nature.com/articles/s41893-018-0021-4|journal=Nature Sustainability |language=en |volume=1 |issue=2 |pages=88–95 |doi=10.1038/s41893-018-0021-4|bibcode=2018NatSu...1...88O |s2cid=169679920|issn=2398-9629}}</ref>

== Cultural and historical viewpoint ==
{{Main|Earth in culture|Earth symbol}}
[[File:Tracy Caldwell Dyson in Cupola ISS.jpg|alt=Woman seeing the Earth from space through a window|thumb|[[Tracy Caldwell Dyson]], a [[NASA]] astronaut, observing Earth from the [[Cupola (ISS module)|''Cupola'' module]] at the [[International Space Station]] on 11 September 2010]]
[[Culture|Human cultures]] have developed many views of the planet.<ref name="NYT-20181224b">{{cite news |last=Widmer |first=Ted |author-link=Edward L. Widmer|title=What Did Plato Think the Earth Looked Like? – For millenniums, humans have tried to imagine the world in space. Fifty years ago, we finally saw it. |url=https://www.nytimes.com/2018/12/24/opinion/plato-earth-christmas-eve-apollo-8.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2018/12/24/opinion/plato-earth-christmas-eve-apollo-8.html |archive-date=1 January 2022 |url-access=limited |date=24 December 2018 |work=[[The New York Times]] |access-date=25 December 2018}}{{cbignore}}</ref> The standard [[astronomical symbols]] of Earth are a quartered circle, [[File:Earth symbol (fixed width).svg|🜨]],<ref name="liungman2004" /> representing the [[four corners of the world]], and a [[globus cruciger]], [[File:globus cruciger (fixed width).svg|♁]]. Earth is sometimes [[Personification|personified]] as a [[deity]]. In many cultures it is a [[mother goddess]] that is also the primary [[fertility deity]].<ref name="Stookey-2004">{{Cite book |title=Thematic Guide to World Mythology |last=Stookey |first=Lorena Laura |publisher=Greenwood Press |year=2004 |isbn=978-0-313-31505-3 |location=Westport, CN |pages=[https://archive.org/details/thematicguidetow00lore/page/114 114–115] |url=https://archive.org/details/thematicguidetow00lore/page/114}}</ref> [[Creation myth]]s in many religions involve the creation of Earth by a supernatural deity or deities.<ref name="Stookey-2004" /> The [[Gaia hypothesis]], developed in the mid-20th century, compared Earth's environments and life as a single self-regulating organism leading to broad stabilization of the conditions of habitability.<ref>{{cite book|last1=Lovelock|first1=James E.|author-link=James Lovelock|title=The Vanishing Face of Gaia |publisher=Basic Books|year=2009|page=255|isbn=978-0-465-01549-8}}</ref><ref>{{cite journal|last=Lovelock|first=James E.|author-link=James Lovelock |year=1972 |title=Gaia as seen through the atmosphere|journal=Atmospheric Environment |volume=6|issue=8 |pages=579–580|bibcode=1972AtmEn...6..579L |doi=10.1016/0004-6981(72)90076-5 |issn=1352-2310}}</ref><ref>{{Cite journal |last1=Lovelock |first1=J.E. |last2=Margulis |first2=L. |author2-link=Lynn Margulis |date=1974 |title=Atmospheric homeostasis by and for the biosphere: the gaia hypothesis |journal=Tellus A |volume=26 |issue=1–2 |pages=2–10 |doi=10.3402/tellusa.v26i1-2.9731 |doi-access=free |s2cid=129803613 |language=en |bibcode=1974Tell...26....2L }}</ref>

[[Timeline of first images of Earth from space|Images of Earth taken from space]], particularly during the Apollo program, have been credited with altering the way that people viewed the planet that they lived on, called the [[overview effect]], emphasizing its beauty, uniqueness and apparent fragility.<ref>{{cite news|last=Overbye|first=Dennis|author-link=Dennis Overbye|date=21 December 2018|title=Apollo 8's Earthrise: The Shot Seen Round the World – Half a century ago today, a photograph from the moon helped humans rediscover Earth.|work=[[The New York Times]]|url=https://www.nytimes.com/2018/12/21/science/earthrise-moon-apollo-nasa.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2018/12/21/science/earthrise-moon-apollo-nasa.html |archive-date=1 January 2022 |url-access=limited|access-date=24 December 2018}}{{cbignore}}</ref><ref>{{cite news|last1=Boulton|first1=Matthew Myer|last2=Heithaus|first2=Joseph|date=24 December 2018|title=We Are All Riders on the Same Planet – Seen from space 50 years ago, Earth appeared as a gift to preserve and cherish. What happened?|work=[[The New York Times]] |url=https://www.nytimes.com/2018/12/24/opinion/earth-space-christmas-eve-apollo-8.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2018/12/24/opinion/earth-space-christmas-eve-apollo-8.html |archive-date=1 January 2022 |url-access=limited|access-date=25 December 2018}}{{cbignore}}</ref> In particular, this caused a realization of the scope of effects from human activity on Earth's environment. Enabled by science, particularly [[Earth observation]],<ref>{{cite web |title=ESPI Evening Event "Seeing Our Planet Whole: A Cultural and Ethical View of Earth Observation" |website=ESPI – European Space Policy Institute |date=7 October 2021 |url=https://espi.or.at/news/espi-evening-event-seeing-our-planet-whole-a-cultural-and-ethical-view-of-earth-observation |access-date=27 January 2022}}</ref> humans have started to take [[Environmentalism|action on environmental issues]] globally,<ref>{{cite web |title=Two early images of Earth that bolstered the environmental movement – CBC Radio |website=CBC |date=16 April 2020 |url=https://www.cbc.ca/radio/quirks/two-early-images-of-earth-that-bolstered-the-environmental-movement-1.5534843 |access-date=27 January 2022}}</ref> acknowledging the impact of humans and the [[Ecological network|interconnectedness of Earth's environments]].

Scientific investigation has resulted in several culturally transformative shifts in people's view of the planet. Initial belief in a [[flat Earth]] was gradually displaced in [[Ancient Greece]] by the idea of a [[spherical Earth]], which was attributed to both the philosophers [[Pythagoras]] and [[Parmenides]].<ref>{{cite book |last=Kahn |first=Charles H. | author-link = Charles H. Kahn |date=2001 |title=Pythagoras and the Pythagoreans: A Brief History |url={{GBurl|id=GKUtAwAAQBAJ|q=Pythagoreanism|p=72}} |location=Indianapolis, IN and Cambridge, England |publisher=Hackett Publishing Company |isbn=978-0-87220-575-8 |page=53}}</ref><ref>{{Cite book |last=Garwood|first=Christine|url=https://www.worldcat.org/oclc/184822945|title=Flat earth : the history of an infamous idea|date=2008|publisher=Thomas Dunne Books |isbn=978-0-312-38208-7 |edition=1st|location=New York|oclc=184822945|pages=26–31}}</ref> Earth was generally believed to be [[Geocentric model|the center of the universe]] until the 16th century, when scientists first concluded that it was [[heliocentrism|a moving object]], one of the planets of the Solar System.<ref name="arnett20060716" />

It was only during the 19th century that geologists realized [[Earth's age]] was at least many millions of years.<ref>{{Cite book |title=Physical Geology: Exploring the Earth |last1=Monroe |first1=James |publisher=Thomson Brooks/Cole |year=2007 |isbn=978-0-495-01148-4 |pages=263–265 |last2=Wicander |first2=Reed |last3=Hazlett |first3=Richard}}</ref> [[Lord Kelvin]] used [[thermodynamics]] to estimate the age of Earth to be between 20 million and 400&nbsp;million years in 1864, sparking a vigorous debate on the subject; it was only when radioactivity and [[Radiometric dating|radioactive dating]] were discovered in the late 19th and early 20th centuries that a reliable mechanism for determining Earth's age was established, proving the planet to be billions of years old.<ref>{{Cite book |title=An Equation for Every Occasion: Fifty-Two Formulas and Why They Matter |last=Henshaw |first=John M. |publisher=Johns Hopkins University Press |year=2014 |isbn=978-1-4214-1491-1 |pages=117–118}}</ref><ref>{{Cite book |title=Lord Kelvin and the Age of the Earth |last=Burchfield |first=Joe D. |publisher=University of Chicago Press |year=1990 |isbn=978-0-226-08043-7 |pages=13–18}}</ref>

== See also ==
{{columns list|colwidth=22em|
* [[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 ==
<!-- List alphabetized. Please keep it that way, thank you!
-->
{{reflist |30em |group="n" |refs=

<ref name="Aoki">The ultimate source of these figures, uses the term "seconds of UT1" instead of "seconds of mean solar time".—{{cite journal |last1=Aoki |first1=S. |title=The new definition of universal time |journal=Astronomy and Astrophysics |year=1982 |volume=105 |issue=2 |pages=359–361 |bibcode=1982A&A...105..359A |last2=Kinoshita |first2=H. |last3=Guinot |first3=B. |last4=Kaplan |first4=G. H. |last5=McCarthy |first5=D. D. |last6=Seidelmann |first6=P. K.}}</ref>

<ref name="apsis">aphelion = ''a'' × (1 + ''e''); perihelion = ''a'' × (1&nbsp;– ''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.—{{cite book|page=144|title=Probing the New Solar System|last1=Wilkinson|first1=John|year= 2009|publisher=CSIRO Publishing|isbn=978-0-643-09949-4}}</ref>

<ref name="epoch">All astronomical quantities vary, both [[Secular phenomena|secularly]] and [[Frequency|periodically]]. The quantities given are the values at the instant [[J2000.0]] of the secular variation, ignoring all periodic variations.</ref>

<ref name="hill_radius">For Earth, the [[Hill radius]] is <math>R_H = a\left ( \frac{m}{3M} \right )^{\frac{1}{3}}</math>, 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 <math>\left ( \frac{1}{3 \cdot 332,946} \right )^{\frac{1}{3}} = 0.01</math>.</ref>

<ref name="jaes41_3_379">Including the [[Somali Plate]], which is being formed out of the African Plate. See: {{cite journal |first=Jean |last=Chorowicz |date=October 2005 |title=The East African rift system |journal=[[Journal of African Earth Sciences]] |volume=43 |issue=1–3 |pages=379–410 |doi=10.1016/j.jafrearsci.2005.07.019 |bibcode=2005JAfES..43..379C}}</ref>

<ref name="solar_energy">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.</ref>

<ref name="surfacecover">Due to natural fluctuations, ambiguities surrounding [[Ice shelf|ice shelves]], and mapping conventions for [[vertical datum]]s, exact values for land and ocean coverage are not meaningful. Based on data from the [[Vector Map]] and [http://www.landcover.org/ Global Landcover] {{Webarchive|url=https://web.archive.org/web/20150326085837/http://www.landcover.org/ |date=26 March 2015}} 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.</ref>

<ref name="space_debris">As of 4 January 2018, the United States Strategic Command tracked a total of 18,835 artificial objects, mostly debris. See: {{cite journal |url=https://orbitaldebris.jsc.nasa.gov/quarterly-news/pdfs/odqnv22i1.pdf |title=Satellite Box Score |journal=Orbital Debris Quarterly News |editor1-first=Phillip |editor1-last=Anz-Meador |editor2-first=Debi |editor2-last=Shoots |volume=22 |issue=1 |page=12 |date=February 2018 |access-date=18 April 2018}}</ref>

}}

== References ==
<!--
 List alphabetized. Keep it that way!
-->
{{reflist|refs=

<ref name="aaa428_261">{{cite journal |display-authors=1 |last1=Laskar |first1=J. |last2=Robutel |first2=P. |last3=Joutel |first3=F. |last4=Gastineau |first4=M. |last5=Correia |first5=A.C.M. |last6=Levrard |first6=B. |title=A long-term numerical solution for the insolation quantities of the Earth |journal=Astronomy and Astrophysics |year=2004 |volume=428 |issue=1 |pages=261–285 |bibcode=2004A&A...428..261L |doi=10.1051/0004-6361:20041335 |url=https://hal.archives-ouvertes.fr/hal-00001603/document |doi-access=free }}</ref>

<ref name="ab2003">{{cite web |author=Staff |date=September 2003 |url=http://astrobiology.arc.nasa.gov/roadmap/g1.html |archive-url=https://web.archive.org/web/20120312212337/http://astrobiology.arc.nasa.gov/roadmap/g1.html |archive-date=12 March 2012 |title=Astrobiology Roadmap |publisher=NASA, Lockheed Martin |access-date=10 March 2007 |url-status=dead}}</ref>

<ref name="abedon1997">{{cite web |last1=Abedon |first1=Stephen T. |date=31 March 1997 |url=http://www.mansfield.ohio-state.edu/~sabedon/biol1010.htm |archive-url=https://web.archive.org/web/20121129043509/http://www.mansfield.ohio-state.edu/~sabedon/biol1010.htm |archive-date=29 November 2012 |title=History of Earth |publisher=Ohio State University |access-date=19 March 2007 |url-status=dead}}</ref>

<ref name="age_earth1">See:
* {{cite book |first1=G. Brent |last1=Dalrymple |author-link1=Brent Dalrymple|date=1991 |title=The Age of the Earth |publisher=Stanford University Press |location=California |isbn=978-0-8047-1569-0}}
* {{cite web |last=Newman |first=William L. |date=9 July 2007 |url=http://pubs.usgs.gov/gip/geotime/age.html |title=Age of the Earth |publisher=Publications Services, USGS |access-date=20 September 2007}}
* {{cite journal |last1=Dalrymple |first1=G. Brent |author-link1=Brent Dalrymple|title=The age of the Earth in the twentieth century: a problem (mostly) solved |journal=Geological Society, London, Special Publications |year=2001 |volume=190 |issue=1 |pages=205–221 |url=http://sp.lyellcollection.org/cgi/content/abstract/190/1/205 |access-date=20 September 2007 |doi=10.1144/GSL.SP.2001.190.01.14 |bibcode=2001GSLSP.190..205D|s2cid=130092094 }}</ref>

<ref name="aj136_5_1906">{{cite journal |last1=McCarthy |first1=Dennis D. |author-link1=Dennis McCarthy (scientist)|last2=Hackman |first2=Christine |last3=Nelson |first3=Robert A. |title=The Physical Basis of the Leap Second |journal=The Astronomical Journal |volume=136 |issue=5 |pages=1906–1908 |date=November 2008 |doi=10.1088/0004-6256/136/5/1906 |bibcode=2008AJ....136.1906M |doi-access=free}}</ref>

<ref name="ajes38_613">{{cite journal |last1=Armstrong |first1=R. L. |year=1991 |title=The persistent myth of crustal growth |journal=Australian Journal of Earth Sciences |volume=38 |issue=5 |pages=613–630 |doi=10.1080/08120099108727995 |bibcode=1991AuJES..38..613A |url=http://www.mantleplumes.org/WebDocuments/Armstrong1991.pdf |citeseerx=10.1.1.527.9577}}</ref>

<ref name="Allen294">{{cite book |title=Allen's Astrophysical Quantities |last1=Allen |first1=Clabon Walter |author-link1=Clabon Allen |last2=Cox |first2=Arthur N. |editor=Arthur N. Cox |publisher=Springer |date=2000 |isbn=978-0-387-98746-0 |url={{GBurl|id=w8PK2XFLLH8C|p=294}} |page=294 |access-date=13 March 2011}}</ref>

<ref name="Allen296">{{cite book |title=Allen's Astrophysical Quantities |last1=Allen |first1=Clabon Walter |author-link1=Clabon Allen|last2=Cox |first2=Arthur N. |editor=Arthur N. Cox |publisher=Springer |date=2000 |isbn=978-0-387-98746-0 |url={{GBurl|id=w8PK2XFLLH8C|p=296}} |page=296 |access-date=17 August 2010}}</ref>

<ref name="amnat163_2_192">{{cite journal |last1=Hillebrand |first1=Helmut |title=On the Generality of the Latitudinal Gradient |journal=American Naturalist |year=2004 |volume=163 |issue=2 |pages=192–211 |doi=10.1086/381004 |pmid=14970922 |s2cid=9886026 |url=http://oceanrep.geomar.de/4048/1/Hillebrand_2004_Amer_nat.pdf}}</ref>

<ref name="angular">{{cite web |last1=Williams |first1=David R. |date=10 February 2006 |url=http://nssdc.gsfc.nasa.gov/planetary/planetfact.html |title=Planetary Fact Sheets |publisher=NASA |access-date=28 September 2008|at=See the apparent diameters on the Sun and Moon pages}}</ref>
<!---
<ref name=arghg4_143>{{cite journal |last1=Pennock |first1=R. T. |title=Creationism and intelligent design |journal=Annual Review of Genomics and Human Genetics |volume=4 |issue=1 |pages=143–163 |year=2003 |pmid=14527300 |doi=10.1146/annurev.genom.4.070802.110400}}</ref>
--->
<ref name="arnett20060716">{{cite web |first1=Bill |last1=Arnett |date=16 July 2006 |title=Earth |work=The Nine Planets, A Multimedia Tour of the Solar System: one star, eight planets, and more |url=http://nineplanets.org/earth.html |access-date=9 March 2010}}</ref>

<ref name="arwps4_265">{{cite journal |last1=Hunten |first1=D. M. |title=Hydrogen loss from the terrestrial planets |journal=Annual Review of Earth and Planetary Sciences |year=1976 |volume=4 |issue=1 |pages=265–292 |bibcode=1976AREPS...4..265H |doi=10.1146/annurev.ea.04.050176.001405 |last2=Donahue |first2=T. M|author-link2=Thomas Michael Donahue}}</ref>

<ref name="asp2002">{{cite conference |last1=Guinan |first1=E. F. |last2=Ribas |first2=I. |editor=Benjamin Montesinos, Alvaro Gimenez and Edward F. Guinan |title=Our Changing Sun: The Role of Solar Nuclear Evolution and Magnetic Activity on Earth's Atmosphere and Climate |work=ASP Conference Proceedings: The Evolving Sun and its Influence on Planetary Environments |year=2002 |location=San Francisco |isbn=978-1-58381-109-2 |publisher=Astronomical Society of the Pacific |bibcode=2002ASPC..269...85G}}</ref>

<ref name="asu_highest_temp">{{cite web |url=https://wmo.asu.edu/content/world-highest-temperature |title=World: Highest Temperature |work=[[WMO]] Weather and Climate Extremes Archive |publisher=[[Arizona State University]] |access-date=6 September 2020}}</ref>

<ref name="asu_lowest_temp">{{cite web |url=https://wmo.asu.edu/content/world-lowest-temperature |title=World: Lowest Temperature |work=[[WMO]] Weather and Climate Extremes Archive |publisher=[[Arizona State University]] |access-date=6 September 2020}}</ref>

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<ref name="britt2000">{{cite web |first1=Robert |last1=Britt |website=Space.com|url=http://www.space.com/scienceastronomy/solarsystem/death_of_earth_000224.html |title=Freeze, Fry or Dry: How Long Has the Earth Got? |date=25 February 2000 |url-status=dead |archive-url=https://web.archive.org/web/20090605231345/http://www.space.com/scienceastronomy/solarsystem/death_of_earth_000224.html |archive-date=5 June 2009}}</ref>

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<ref name="brown_mussett1981">{{cite book |last1=Brown |first1=Geoff C. |last2=Mussett |first2=Alan E. |title=The Inaccessible Earth |edition=2nd |date=1981 |page=[https://archive.org/details/inaccessibleeart0000brow_r5i2/page/166 166] |publisher=Taylor & Francis |isbn=978-0-04-550028-4 |url=https://archive.org/details/inaccessibleeart0000brow_r5i2/page/166}} Note: After Ronov and Yaroshevsky (1969).</ref>

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<ref name=cazenave_ahrens1995>{{cite book |first1=Anny |last1=Cazenave |author-link=Anny Cazenave |editor=Ahrens, Thomas J |date=1995 |title=Global Earth Physics: A Handbook of Physical Constants |issue=1 |publisher=American Geophysical Union |location=Washington, DC |isbn=978-0-87590-851-9 |chapter-url=http://www.agu.org/reference/gephys/5_cazenave.pdf |archive-url=https://web.archive.org/web/20061016024803/http://www.agu.org/reference/gephys/5_cazenave.pdf |archive-date=16 October 2006 |access-date=3 August 2008 |chapter=Geoid, Topography and Distribution of Landforms |series=AGU Reference Shelf |volume=1 |doi=10.1029/RF001 |bibcode=1995geph.conf.....A}}</ref>

<ref name=Choi>{{cite web |last1=Choi |first1=Charles Q. |title=First Asteroid Companion of Earth Discovered at Last |website=[[Space.com]]|url=http://www.space.com/12443-earth-asteroid-companion-discovered-2010-tk7.html |date=27 July 2011 |access-date=27 July 2011}}</ref>

<ref name=christou_asher2011>{{cite journal |last1=Christou |first1=Apostolos A. |last2=Asher |first2=David J. |author-link2=David J. Asher|date=31 March 2011 |title=A long-lived horseshoe companion to the Earth |arxiv=1104.0036 |doi=10.1111/j.1365-2966.2011.18595.x |volume=414 |issue=4 |journal=Monthly Notices of the Royal Astronomical Society |pages=2965–2969 |bibcode=2011MNRAS.414.2965C|s2cid=13832179 }} See table 2, p. 5.</ref>

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<ref name=layers_earth>{{cite web |author=Staff |url=http://volcano.oregonstate.edu/vwdocs/vwlessons/plate_tectonics/part1.html |archive-url=https://web.archive.org/web/20130211014443/http://volcano.oregonstate.edu/vwdocs/vwlessons/plate_tectonics/part1.html |archive-date=11 February 2013 |title=Layers of the Earth |work=Volcano World|publisher=Oregon State University|access-date=11 March 2007 |url-status=dead}}</ref>

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<ref name=liungman2004>{{cite book |first1=Carl G. |last1=Liungman |date=2004 |chapter=Group 29: Multi-axes symmetric, both soft and straight-lined, closed signs with crossing lines |title=Symbols&nbsp;– Encyclopedia of Western Signs and Ideograms |pages=281–282 |publisher=Ionfox AB |location=New York |isbn=978-91-972705-0-2}}</ref>

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<ref name=earthmass>{{cite web |url=https://ssd.jpl.nasa.gov/planets/phys_par.html |title=Planetary Physical Parameters |publisher=[[Jet Propulsion Laboratory]] |date=2008 |access-date=11 August 2022}}</ref>

<ref name=Narottam2008>{{cite book |url={{GBurl|id=i4kASIoKym8C|p=40}} |title=Climate Change and International Politics |publisher=Kalpaz Publications |first=Narottam |last=Gaan |page=40 |year=2008 |isbn=978-81-7835-641-9}}</ref>
}}

== External links ==
{{Spoken Wikipedia|En-Earth-article.ogg|date=22 April 2021}}
* [https://solarsystem.nasa.gov/planets/earth/overview/ Earth&nbsp;– Profile] – Solar System Exploration – [[NASA]]
* [http://earthobservatory.nasa.gov/ Earth Observatory] – NASA
* Earth – Videos – International Space Station:
** [https://www.youtube.com/watch?v=74mhQyuyELQ Video (01:02)] on YouTube – Earth (time-lapse)
** [https://www.youtube.com/watch?v=l6ahFFFQBZY Video (00:27)] on YouTube – Earth and [[aurora]]s (time-lapse)
* [https://www.google.com/maps/@36.6233227,-44.9959756,5662076m/data=!3m1!1e3 Google Earth 3D], interactive map
* [https://thehappykoala.github.io/Harmony-of-the-Spheres/#/category/Solar%20System/scenario/The%20Earth%20and%20Moon%20System Interactive 3D visualization of the Sun, Earth and Moon system]
* [http://portal.gplates.org/ GPlates Portal] (University of Sydney)

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