Earth

=== 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]], with the [[shelf sea]]s covering the [[continental shelf|shelves]] of the [[continental crust]] to a lesser extent. 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>