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{{About|the planet}}
<br><br>
{{pp-semi|small=yes}}{{pp-move-indef}}
{{Infobox planet
| bgcolour = #c0c0ff
| name = Earth
| symbol = [[File:Earth symbol.svg|25px|Astronomical symbol of Earth]]
| image =  [[File:The Earth seen from Apollo 17.jpg|270px|"[[The Blue Marble]]" photograph of Earth, taken by the ''[[Apollo 17]]'' lunar mission|alt=A planetary disk of white cloud formations, brown and green land masses, and dark blue oceans against a black background. The Arabian peninsula, Africa and Madagascar lie in the upper half of the disk, while Antarctica is at the bottom.]]
| caption =  "[[The Blue Marble]]" photograph of Earth, <br>taken by the ''[[Apollo 17]]'' lunar mission
| alt_names =
| flag = {{flagicon|world}}
| epoch = [[J2000.0]]<ref group=note name=epoch/>
| aphelion = {{val|152098232|u=km}}<br> {{val|1.01671388|ul=AU}}<ref group=note name=apsis/>
| perihelion = {{val|147098290|u=km}}<br> {{val|0.98329134|u=AU}}<ref group=note name=apsis/>
| semimajor = {{val|149598261|u=km}}<br> {{val|1.00000261|u=AU}}<ref name=standish_williams_iau/>
| eccentricity = {{val|0.01671123}}<ref name=standish_williams_iau/>
| inclination = {{val|7.155|s=°}} to [[Sun]]'s [[equator]]<br>1.57869°<ref name=Allen294/> to [[invariable plane]]
| asc_node = {{val|348.73936|s=°}}<ref name="earth_fact_sheet"/><ref group=note name=asc_node/>
| arg_peri = {{val|114.20783|s=°}}<ref name="earth_fact_sheet"/><ref group=note name=arg_peri/>
| mean_anomaly = {{val|357.51716|s=°}}<ref name="earth_fact_sheet"/>
| period = {{val|365.256363004|u=days}}<ref name="IERS"/><br>{{val|1.000017421|u=[[Julian year (astronomy)|yr]]}}
| avg_speed = {{val|29.78|ul=km/s}}<ref name="earth_fact_sheet"/><br>{{val|107200|ul=km/h}}
| satellites = 1 natural&nbsp;(the [[Moon]]),<br> 1070 operational [[artificial satellite]]s, & {{val|21000}} pieces of debris > 10 cm ({{as of|2013|10|24|lc=on}})<ref>{{cite web|url=http://www.universetoday.com/42198/how-many-satellites-in-space/|title=How Many Satellites are in Space?|publisher=Universe Today|date=2013-10-24|accessdate=2014-02-01}}</ref>
| allsatellites=yes
| physical_characteristics = yes
| flattening = {{val|0.0033528}}<ref name=iers/>
| equatorial_radius = {{val|6378.1|u=km}}<ref name=usno/><ref name="WGS-84"/>
| polar_radius = {{val|6356.8|u=km}}<ref name=cazenave_ahrens1995/>
| mean_radius = {{val|6371.0|u=km}}<ref name=hbcp2000/>
| circumference = {{val|40075.017|u=km}} ([[equator]]ial)<ref name="WGS-84">[[World Geodetic System]] (''WGS-84''). [http://earth-info.nga.mil/GandG/wgs84/ Available online] from [[National Geospatial-Intelligence Agency]].</ref><br>{{val|40007.86|u=km}} ([[meridional]])<ref name="WGS-84-2"/><ref name="circ">The Earth's [[circumference]] is almost exactly 40,000 km because the [[metre]] was calibrated on this measurement&nbsp;– more specifically, 1/10-millionth of the distance between the poles and the equator.</ref>
| surface_area = {{val|510072000|u=km2}}<ref name="Pidwirny 2006_8" /><ref name=cia /><ref group=note name=surfacecover/><br>
{{nowrap|{{val|148940000|u=km2}} (29.2%) land}}<br>
{{nowrap|{{val|361132000|u=km2}} (70.8 %) water}}
| volume = {{val|1.08321|e=12|u=km3}}<ref name="earth_fact_sheet"/> ([[volume of the Earth]])
| mass = {{val|5.97219|e=24|u=kg}}<ref>{{cite web |url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Earth&Display=Facts |title=Solar System Exploration: Earth: Facts & Figures |work=NASA |date=13 Dec 2012 |accessdate=2012-01-22}}</ref><br>
3.0{{e|-6}}&nbsp;Suns
| density = {{val|5.515|u=g/cm3}}<ref name="earth_fact_sheet"/>
| surface_grav = {{val|9.780327|ul=m/s2}}<ref name="yoder12"/><br>{{val|0.99732|u=''[[g-force|g]]''}} ([[Earth gravity]])
| escape_velocity = {{val|11.186|u=km/s}}<ref name="earth_fact_sheet"/>
| sidereal_day = {{val|0.99726968|u=d}}<ref name=Allen296 /> <br>23{{smallsup|h}}&nbsp;56{{smallsup|m}}&nbsp;4.100{{smallsup|s}}
| rot_velocity = {{convert|1674.4|km/h|m/s|abbr=on}}<ref name="Cox2000"/>
| axial_tilt = 23°26′21.4119″<ref name="IERS"/>
| albedo = 0.367 ([[Geometric albedo|geometric]])<ref name="earth_fact_sheet"/><br />
0.306 ([[Bond albedo|Bond]])<ref name="earth_fact_sheet"/>
| atmosphere = yes
| temperatures = yes
| temp_name1 = [[Kelvin]]
| min_temp_1 = 184&nbsp;K<ref name=asu_lowest_temp/>
| mean_temp_1 = 288&nbsp;K<ref name=kinver20091210/>
| max_temp_1 = 330&nbsp;K<ref name=asu_highest_temp/>
| temp_name2 = [[Celsius]]
| min_temp_2 = −89.2&nbsp;°C
| mean_temp_2 = 15&nbsp;°C
| max_temp_2 = 56.7&nbsp;°C
| surface_pressure = {{val|101.325|ul=kPa}} (at [[Sea level|MSL]])
| atmosphere_composition = 78.08%&nbsp;[[nitrogen]] (N<sub>2</sub>)<ref name="earth_fact_sheet"/> (dry air)<br> 20.95%&nbsp;[[oxygen]] (O<sub>2</sub>)<br> 0.93%&nbsp;[[argon]]<br> 0.039%&nbsp;[[carbon dioxide]]<ref name=NOAA>[http://www.esrl.noaa.gov/gmd/ccgg/trends/#mlo National Oceanic & Atmospheric Administration (NOAA)&nbsp;– Earth System Research Laboratory (ESRL), Trends in Carbon Dioxide].</ref><br>About 1% [[water vapor]] (varies with [[climate]])
|note = no
}}


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'''Earth''' is the third [[planet]] from the [[Sun]]. It is the [[Density|densest]] and fifth-largest of the eight planets in the [[Solar System]]. It is also the largest of the Solar System's four [[terrestrial planet]]s. It is sometimes referred to as the [[world]] or the Blue Planet.<ref name="blueplanet"/>
 
Earth formed [[Age of the Earth|approximately 4.54 billion years]] ago, and [[Abiogenesis|life appeared]] on its surface within its first billion years.<ref name="age_earth1" /> Earth's [[biosphere]] then significantly altered [[Atmosphere of Earth|the atmospheric]] and other [[abiotic component|basic physical]] conditions, which enabled the proliferation of [[aerobic organism|organisms]] as well as the formation of the [[ozone layer]], which together with [[Earth's magnetic field]] blocked harmful [[sunlight|solar radiation]], and permitted formerly ocean-confined life to move safely to land.<ref name="Harrison 2002" /> The [[Geophysics|physical properties of the Earth]], as well as its [[Geological history of Earth|geological history]] and orbit, have allowed life to persist.
 
Earth's [[lithosphere]] is divided into several rigid segments, or [[Plate tectonics|tectonic plates]], that migrate across the surface over periods of [[Geologic time scale|many millions of years]]. Over 70% percent of Earth's surface is covered with water,<ref>{{cite web|url=http://www.noaa.gov/ocean.html |title=NOAA&nbsp;– Ocean |publisher=Noaa.gov |date= |accessdate=2013-05-03}}</ref> with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the [[hydrosphere]]. Earth's [[Geographical pole|poles]] are mostly covered with ice that is the solid ice of the [[Antarctic ice sheet]] and the [[sea ice]] that is the [[polar ice packs]]. [[Structure of the Earth|The planet's interior]] remains active, with a solid iron [[inner core]], a liquid [[outer core]] that generates the magnetic field, and a thick layer of relatively solid [[Mantle (geology)|mantle]].
 
Earth [[Gravitational interaction|gravitationally interacts]] with other objects in space, especially the Sun and the [[Moon]]. During one orbit around the Sun, the Earth rotates about its own axis 366.26 times, creating 365.26 [[solar time|solar days]], or one [[sidereal year]].<ref group=note name=sidereal_solar/> The Earth's axis of rotation is [[Axial tilt|tilted]] 23.4° away from the [[perpendicular]] of its [[Orbital plane (astronomy)|orbital plane]], producing seasonal variations on the planet's surface with a period of one [[tropical year]] (365.24 solar days).<ref name=yoder1995/> The Moon is Earth's only [[natural satellite]]. It began orbiting the Earth about {{nowrap|4.53 billion years ago (bya)}}. The Moon's gravitational interaction with Earth stimulates ocean [[tide]]s, stabilizes the axial tilt, and gradually slows the planet's rotation.
 
The planet is home to millions of [[species]] of [[life]], including [[human]]s.<ref name=science_241_4872_1441 /> Both the [[mineral]] resources of the planet and the products of the [[biosphere]] contribute resources that are used to support a [[World population|global human population]].<ref name="World_Population_Clock"/> These inhabitants are grouped into about 200 independent [[sovereign state]]s, which interact through diplomacy, travel, trade, and military action.
 
==Name and etymology==
The modern English noun ''earth'' developed from [[Middle English]] ''erthe'' (recorded in 1137), itself from [[Old English]] ''eorthe'' (dating from before 725), deriving from [[Proto-Germanic]] *''erthō''. ''Earth'' has [[cognate]]s in all other [[Germanic languages]], including [[Dutch language|Dutch]] ''aarde'', [[German language|German]] ''Erde'', and [[Swedish language|Swedish]], [[Norwegian language|Norwegian]], and [[Danish language|Danish]] ''jord''.<ref name="BARNHART228-229">[[Robert Barnhart|Barnhart, Robert K.]] (1995).
 
Originally. from a Semitic (Arabic/Hebrew) root: أرض| aarth-or, ארץ aerets (Hebrew) is the word for land, country and Earth.
 
As per later Germanic roots, the Barnhart Concise Dictionary of Etymology, pages 228–229. [[HarperCollins]]. ISBN 0-06-270084-7</ref> The Earth is personified as a goddess in [[Germanic paganism]] (appearing as [[Jörð]] in [[Norse mythology]], mother of the god [[Thor]]).<ref name="SIMEK179">[[Rudolf Simek|Simek, Rudolf]] (2007) translated by Angela Hall. ''Dictionary of Northern Mythology'', page 179. [[Boydell & Brewer|D.S. Brewer]] ISBN 0-85991-513-1</ref>
 
In general English usage, the name ''earth'' can be capitalized or spelled in lowercase interchangeably, either when used absolutely or prefixed with "the" (i.e. "Earth", "the Earth", "earth", or "the earth"). Many deliberately spell the name of the planet with a capital, both as "Earth" or "the Earth". This is to distinguish it as a proper noun, distinct from the senses of the term as a [[mass noun]] or verb (e.g. referring to soil, the ground, earthing in the electrical sense, etc.). [[Oxford spelling]] recognizes the lowercase form as the most common, with the capitalized form as a variant of it. Another common convention is to spell the name with a capital when occurring absolutely (e.g. [[Earth's atmosphere]]) and lowercase when preceded by "the" (e.g. the atmosphere of the earth). The term almost exclusively exists in lowercase when appearing in common phrases, even without "the" preceding it (e.g. "It does not cost the earth.", "What on earth are you doing?").<ref name="oxford">{{cite dictionary |editor=J. Pearsall |encyclopedia=The New Oxford Dictionary of English |title=earth |url= |accessdate= |edition=1st |year=1998 |publisher=Oxford University Press |volume= |location= |id= |isbn=0-19-861263-X}}</ref>
 
==Composition and structure==
{{Main|Earth science}}
{{Further|Earth physical characteristics tables}}
Earth is a terrestrial planet, meaning that it is a rocky body, rather than a [[gas giant]] like [[Jupiter]]. It is the largest of the four terrestrial planets in size and mass. Of these four planets, Earth also has the highest density, the highest [[surface gravity]], the strongest magnetic field, and fastest rotation,<ref name=stern20011125/> and is probably the only one with active [[plate tectonics]].<ref name=science288_5473_2002/>
 
===Shape===
{{Main|Figure of the Earth}}
[[File:ISS034E016601 - Stratocumulus Clouds - Pacific Ocean.jpg|thumb||thumb|300px|Stratocumulus clouds over the Pacific, viewed from orbit.]]
<!--[[File:Volcán Chimborazo, "El Taita Chimborazo".jpg|thumb|[[Chimborazo (volcano)|Chimborazo]], [[Ecuador]]. The furthermost point on the Earth's surface from its center.<ref>{{cite web|url=http://www.npr.org/templates/story/story.php?storyId=9428163 |title=The 'Highest' Spot on Earth |publisher=Npr.org |date=2007-04-07 |accessdate=2012-07-31}}</ref>]]-->
The shape of the Earth approximates an [[oblate spheroid]], a sphere flattened along the axis from pole to pole such that there is a [[equatorial bulge|bulge]] around the [[equator]].<ref name=milbert_smith96/> This bulge results from the [[rotation]] of the Earth, and causes the diameter at the equator to be {{val|43|ul=km}} (kilometer) larger than the [[Geographical pole|pole]]-to-pole diameter.<ref name="ngdc2006"/> For this reason the furthest point on the surface from the Earth's center of mass is the [[Chimborazo (volcano)|Chimborazo]] volcano in [[Ecuador]].<ref>[http://www.npr.org/templates/story/story.php?storyId=9428163 The 'Highest' Spot on Earth?] NPR.org Consultado el 25-07-2010</ref> The average diameter of the reference spheroid is about {{val|12742|u=km}}, which is approximately 40,000&nbsp;km/[[pi|π]], as the [[Meter#Meridional definition|meter]] was originally defined as 1/10,000,000 of the distance from the equator to the [[North Pole]] through [[Paris]], [[France]].<ref name=nist_length2000/>
 
Local [[topography]] deviates from this idealized spheroid, although on a global scale, these deviations are small: Earth has a [[tolerance (engineering)|tolerance]] of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in [[billiard ball]]s.<ref name=wpba2001/> The largest local deviations in the rocky surface of the Earth are [[Mount Everest]] (8,848&nbsp;m above local sea level) and the [[Mariana Trench]] ({{val|10911|ul=m}} below local sea level). Due to the equatorial bulge, the surface locations farthest from the center of the Earth are the summits of [[Chimborazo (volcano)|Mount Chimborazo]] in [[Ecuador]] and [[Huascarán]] in [[Peru]].<ref name=ps20_5_16/><ref name=lancet365_9462_831/><ref name=tall_tales/>
 
{| class="wikitable" style="float: right; clear: right; margin-left: 2em;"
|+ Chemical composition of the crust<ref name=brown_mussett1981/>
!rowspan="2"|Compound
!rowspan="2"|Formula
!colspan="2"|Composition
|-
!style="font-size: smaller;"|Continental
!style="font-size: smaller;"|Oceanic
|-
|[[silica]]
|style="text-align: center;"|SiO<sub>2</sub>
|style="text-align: right;"|60.2%
|style="text-align: right;"|48.6%
|-
|[[alumina]]
|style="text-align: center;"|Al<sub>2</sub>O<sub>3</sub>
|style="text-align: right;"|15.2%
|style="text-align: right;"|16.5%
|-
|[[Calcium oxide|lime]]
|style="text-align: center;"|CaO
|style="text-align: right;"|5.5%
|style="text-align: right;"|12.3%
|-
|[[Magnesium oxide|magnesia]]
|style="text-align: center;"|MgO
|style="text-align: right;"|3.1%
|style="text-align: right;"|6.8%
|-
|[[iron(II) oxide]]
|style="text-align: center;"|FeO
|style="text-align: right;"|3.8%
|style="text-align: right;"|6.2%
|-
|[[sodium oxide]]
|style="text-align: center;"|Na<sub>2</sub>O
|style="text-align: right;"|3.0%
|style="text-align: right;"|2.6%
|-
|[[potassium oxide]]
|style="text-align: center;"|K<sub>2</sub>O
|style="text-align: right;"|2.8%
|style="text-align: right;"|0.4%
|-
|[[iron(III) oxide]]
|style="text-align: center;"|Fe<sub>2</sub>O<sub>3</sub>
|style="text-align: right;"|2.5%
|style="text-align: right;"|2.3%
|-
|[[water (molecule)|water]]
|style="text-align: center;"|H<sub>2</sub>O
|style="text-align: right;"|1.4%
|style="text-align: right;"|1.1%
|-
|[[carbon dioxide]]
|style="text-align: center;"|CO<sub>2</sub>
|style="text-align: right;"|1.2%
|style="text-align: right;"|1.4%
|-
|[[titanium dioxide]]
|style="text-align: center;"|TiO<sub>2</sub>
|style="text-align: right;"|0.7%
|style="text-align: right;"|1.4%
|-
|[[phosphorus pentoxide]]
|style="text-align: center;"|P<sub>2</sub>O<sub>5</sub>
|style="text-align: right;"|0.2%
|style="text-align: right;"|0.3%
|-
!colspan="2"|Total
!style="text-align: right;"|99.6%
!style="text-align: right;"|99.9%
|}
 
===Chemical composition===
{{See also|Abundance of elements on Earth}}
The mass of the Earth is approximately {{val|5.98|e=24|ul=kg}}. It is composed mostly of [[iron]] (32.1%), [[oxygen]] (30.1%), [[silicon]] (15.1%), [[magnesium]] (13.9%), [[sulfur]] (2.9%), [[nickel]] (1.8%), [[calcium]] (1.5%), and [[aluminium]] (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to [[mass segregation]], the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.<ref name=pnas71_12_6973/>
 
The geochemist [[Frank Wigglesworth Clarke|F. W. Clarke]] calculated that a little more than 47% of the Earth's [[crust (geology)|crust]] consists of oxygen. The more common rock constituents of the Earth's crust are nearly all oxides; chlorine, sulfur and fluorine are the only important exceptions to this and their total amount in any rock is usually much less than 1%. The principal oxides are silica, alumina, iron oxides, lime, magnesia, potash and soda. The silica functions principally as an acid, forming silicates, and all the commonest minerals of igneous rocks are of this nature. From a computation based on 1,672 analyses of all kinds of rocks, Clarke deduced that 99.22% were composed of 11 oxides (see the table at right), with the other constituents occurring in minute quantities.<ref>{{EB1911|title=Petrology |inline=1}}</ref>
 
===Internal structure===
{{Main|Structure of the Earth}}
The interior of the Earth, like that of the other terrestrial planets, is divided into layers by their [[chemical]] or physical ([[Rheology|rheological]]) properties, but unlike the other terrestrial planets, it has a distinct outer and inner core. The outer layer of the Earth is a chemically distinct [[Silicate minerals|silicate]] solid [[crust (geology)|crust]], which is underlain by a highly [[viscous]] solid mantle. The crust is separated from the mantle by the [[Mohorovičić discontinuity]], and the thickness of the crust varies: averaging {{val|6|ul=km}} (kilometers) under the oceans and 30-{{val|50|u=km}} on the continents. The crust and the cold, rigid, top of the [[upper mantle]] are collectively known as the lithosphere, and it is of the lithosphere that the tectonic plates are comprised. Beneath the lithosphere is the [[asthenosphere]], a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and {{val|660|ul=km}} 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 [[inner core]].<ref name=tanimoto_ahrens1995/> The inner core may rotate at a slightly higher [[angular velocity]] than the remainder of the planet, advancing by 0.1–0.5° per year.<ref name=science309_5739_1313/>
 
{| class="wikitable" style="margin:4px; margin-right:0; width:100%; text-align:center;"
|+ Geologic layers of the Earth<ref name=pnas76_9_4192/>
|-
! rowspan="8" style="font-size:smaller; text-align:center; padding:0;"|[[File:Earth-crust-cutaway-english.svg|250px|center]]<br>Earth cutaway from core to exosphere. Not to scale.
!Depth<ref name=robertson2001/><br><span style="font-size: smaller;">km</span>
!style="vertical-align: bottom;"|Component Layer
!Density<br /><span style="font-size: smaller;">g/cm<sup>3</sup></span>
|-
|0–60
|style="text-align:left;"|Lithosphere<ref group="note">Locally varies between 5 and 200&nbsp;km.</ref>
|—
|- style="background:#FEFEFE;"
|0–35
|style="text-align:left; padding-left:1em;"| Crust<ref group="note">Locally varies between 5 and 70&nbsp;km.</ref>
|2.2–2.9
|- style="background:#FEFEFE;"
|35–60
|style="text-align:left; padding-left:1em;"| Upper mantle
|3.4–4.4
|-
|&nbsp;&nbsp;35–2890
|style="text-align:left;"|Mantle
|3.4–5.6
|- style="background:#FEFEFE;"
|100–700
|style="text-align:left; padding-left:1em;"| Asthenosphere
|—
|-
|2890–5100
|style="text-align:left;"|Outer core
|9.9–12.2
|-
|5100–6378
|style="text-align:left;"|Inner core
|12.8–13.1
|}
 
===Heat===
Earth's [[internal heat]] comes from a combination of [[Gravitational binding energy|residual heat from planetary accretion]] (about 20%) and heat produced through [[radioactive decay]] (80%).<ref name="turcotte"/> The major heat-producing isotopes in the Earth are [[Potassium|potassium-40]], [[Uranium|uranium-238]], [[uranium-235]], and [[Thorium|thorium-232]].<ref name=sanders20031210/> At the center of the planet, the temperature may be up to {{convert|6000|Celsius}},<ref>http://www.esrf.eu/news/general/Earth-Center-Hotter/Earth-Centre-Hotter</ref> and the pressure could reach 360&nbsp;[[GPa]].<ref name=ptrsl360_1795_1227/> Because much of the heat is provided by radioactive decay, scientists believe that early in Earth history, before isotopes with short half-lives had been depleted, Earth's heat production would have been much higher. This extra heat production, twice present-day at approximately {{val|3|ul=byr}},<ref name="turcotte" /> would have increased temperature gradients within the Earth, increasing the rates of [[mantle convection]] and plate tectonics, and allowing the production of igneous rocks such as [[komatiites]] that are not formed today.<ref name=epsl121_1/>
 
{| class="wikitable" style="text-align:center;"
|+ Present-day major heat-producing isotopes<ref name="T&S 137"/>
|-
! Isotope
! Heat release<br><span style="font-size: smaller;">{{sfrac|[[Watt|W]]|kg isotope}}</span>
! Half-life<br><br><span style="font-size: smaller;">years</span>
! Mean mantle concentration<br><span style="font-size: smaller;">{{sfrac|kg isotope|kg mantle}}</span>
! Heat release<br><span style="font-size: smaller;">{{sfrac|W|kg mantle}}</span>
|-
| <sup>238</sup>U
| {{nowrap|9.46 × 10<sup>−5</sup>}}
| {{nowrap|4.47 × 10<sup>9</sup>}}
| {{nowrap|30.8 × 10<sup>−9</sup>}}
| {{nowrap|2.91 × 10<sup>−12</sup>}}
|-
| <sup>235</sup>U
| {{nowrap|5.69 × 10<sup>−4</sup>}}
| {{nowrap|7.04 × 10<sup>8</sup>}}
| {{nowrap|0.22 × 10<sup>−9</sup>}}
| {{nowrap|1.25 × 10<sup>−13</sup>}}
|-
| <sup>232</sup>Th
| {{nowrap|2.64 × 10<sup>−5</sup>}}
| {{nowrap|1.40 × 10<sup>10</sup>}}
| {{nowrap|124 × 10<sup>−9</sup>}}
| {{nowrap|3.27 × 10<sup>−12</sup>}}
|-
| <sup>40</sup>K
| {{nowrap|2.92 × 10<sup>−5</sup>}}
| {{nowrap|1.25 × 10<sup>9</sup>}}
| {{nowrap|36.9 × 10<sup>−9</sup>}}
| {{nowrap|1.08 × 10<sup>−12</sup>}}
|}
 
The mean heat loss from the Earth is {{nowrap|87 mW m<sup>−2</sup>}}, for a global heat loss of {{nowrap|4.42 × 10<sup>13</sup> 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 the Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs in the oceans because the crust there is much thinner than that of the continents.<ref name="heat loss" />
 
===Tectonic plates===
{| class="wikitable" style="float:right; margin-left:1em;"
|+ [[List of tectonic plates|Earth's main plates]]<ref name=brown_wohletz2005/>
|-
|colspan="2" style="font-size: smaller; text-align: center;"|[[File:Tectonic plates (empty).svg|250px|alt=Shows the extent and boundaries of tectonic plates, with superimposed outlines of the continents they support]]
|-
!Plate name
!Area<br /><span style="font-size: smaller;">10<sup>6</sup>&nbsp;km<sup>2</sup></span>
|-
| {{legend|#fee6aa|[[Pacific Plate]]}}        ||style="text-align: center;"|103.3
|-
| {{legend|#fb9a7a|[[African Plate]]<ref name=jaes41_3_379 group=note/>}} ||style="text-align: center;"| 78.0
|-
| {{legend|#ac8d7f|[[North American Plate]]}}  ||style="text-align: center;"| 75.9
|-
| {{legend|#7fa172|[[Eurasian Plate]]}}        ||style="text-align: center;"| 67.8
|-
| {{legend|#8a9dbe|[[Antarctic Plate]]}}      ||style="text-align: center;"| 60.9
|-
| {{legend|#fcb482|[[Indo-Australian Plate]]}} ||style="text-align: center;"| 47.2
|-
| {{legend|#ad82b0|[[South American Plate]]}}  ||style="text-align: center;"| 43.6
|}
{{Main|Plate tectonics}}
The mechanically rigid outer layer of the Earth, the lithosphere, is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries: [[Convergent boundary|Convergent boundaries]], at which two plates come together, [[Divergent boundary|Divergent boundaries]], at which two plates are pulled apart, and [[Transform boundary|Transform boundaries]], in which two plates slide past one another laterally. [[Earthquake]]s, volcanic activity, [[Orogeny|mountain-building]], and [[oceanic trench]] formation can occur along these plate boundaries.<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/> and their motion is strongly coupled with convection patterns inside the Earth's mantle.
 
As the tectonic plates migrate across the planet, the ocean floor is [[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 ridge]]s. The combination of these processes continually 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 in age. The oldest oceanic crust is located in the Western Pacific, and has an estimated age of about {{val|200|u=myr}}.<ref name=duennebier1999/><ref name=noaa20070307/> By comparison, the oldest dated continental crust is {{val|4030|u=myr}}.<ref name=cmp134_3/>
 
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 50 and {{val|55|u=mya}}. The fastest-moving plates are the oceanic plates, with the [[Cocos Plate]] advancing at a rate of 75&nbsp;mm/year<ref name=podp2000/> and the Pacific Plate moving 52–69&nbsp;mm/year. At the other extreme, the slowest-moving plate is the Eurasian Plate, progressing at a typical rate of about 21&nbsp;mm/year.<ref name=gps_time_series/>
 
===Surface===
{{Main|Landform|Extreme points of Earth}}
{{Pie chart
|caption = Features of Earth's solid surface shown as percentages of the planet's total surface area
|value1 = 22.1
|label1 = Oceanic ridges
|value2 = 29.8| color1 = silver
|label2 = Ocean basin floors
|value3 = 10.3
|label3 = Continental mountains
|value4 = 18.9
|label4 = Continental lowlands
|value5 = 11.4
|label5 = Continental shelves and slopes
|value6 = 3.8
|label6 = Continental rise
|value7 = 3.7
|label7 = Volcanic island arcs, trenches, submarine volcanoes, and hills}}
The Earth's [[terrain]] varies greatly from place to place. About 70.8%<ref name="Pidwirny 2006_8"/> of the surface is covered by water, with much of the [[continental shelf]] below sea level. This equates to {{val|361.132|end=&nbsp;million|ul=km2}} (139.43 million sq mi).<ref>{{cite web|url=https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html |title=CIA&nbsp;– The World Factbook |publisher=Cia.gov |date= |accessdate=2012-11-02}}</ref> The submerged surface has mountainous features, including a globe-spanning [[mid-ocean ridge]] system, as well as undersea volcanoes,<ref name="ngdc2006" /> [[oceanic trench]]es, [[submarine canyon]]s, [[oceanic plateau]]s and [[abyssal plain]]s. The remaining 29.2% ({{val|148.94|end=&nbsp;million|ul=km2}}, or 57.51 million sq mi) not covered by water consists of mountains, deserts, plains, plateaus, and other [[Geomorphology|geomorphologies]].
 
The planetary surface undergoes reshaping over geological time periods due to [[erosion and tectonics|tectonics and erosion]]. The surface features built up or deformed through plate tectonics are subject to steady [[weathering]] from [[Precipitation (meteorology)|precipitation]], thermal cycles, and chemical effects. [[Glaciation]], [[coastal erosion]], the build-up of [[coral reef]]s, and large meteorite impacts<ref name=kring/> also act to reshape the landscape.
[[File:AYool topography 15min.png|300px|left|thumb|Present-day Earth [[terrain|altimetry]] and [[bathymetry]]. Data from the [[National Geophysical Data Center]]'s [http://www.ngdc.noaa.gov/mgg/topo/ TerrainBase Digital Terrain Model].]]
 
The [[continental crust]] consists of lower density material such as the [[igneous rock]]s [[granite]] and [[andesite]]. Less common is [[basalt]], a denser volcanic rock that is the primary constituent of the ocean floors.<ref name=layers_earth/> [[Sedimentary rock]] is formed from the accumulation of sediment that becomes compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form only about 5% of the crust.<ref name=jessey/> The third form of rock material found on Earth is [[metamorphic rock]], which is created from the transformation of pre-existing rock types through high pressures, high temperatures, or both. The most abundant silicate minerals on the Earth's surface include [[quartz]], the [[feldspar]]s, [[amphibole]], [[mica]], [[pyroxene]] and [[olivine]].<ref name=de_pater_lissauer2010/> Common carbonate minerals include [[calcite]] (found in [[limestone]]) and [[dolomite]].<ref name=wekn_bulakh2004/>
 
The [[pedosphere]] is the outermost layer of the Earth that is composed of soil and subject to [[pedogenesis|soil formation processes]]. It exists at the interface of the [[lithosphere]], atmosphere, [[hydrosphere]] and biosphere. Currently the total arable land is 13.31% of the land surface, with only 4.71% supporting permanent crops.<ref name=cia/> Close to 40% of the Earth's land surface is presently used for cropland and pasture, or an estimated 1.3{{e|7}}&nbsp;km<sup>2</sup> of cropland and 3.4{{e|7}}&nbsp;km<sup>2</sup> of pastureland.<ref name=fao1994/>
 
The elevation of the land surface of the Earth varies from the low point of −418&nbsp;m at the [[Dead Sea]], to a 2005-estimated maximum altitude of 8,848&nbsp;m at the top of [[Mount Everest]]. The mean height of land above sea level is 840&nbsp;m.<ref name=sverdrup/>
 
Besides being divided logically into Northern and Southern Hemispheres centered on the earths poles, the earth has been divided arbitrarily into [[Eastern Hemisphere|Eastern]] and [[Western Hemisphere]]s. The surface of the Earth is traditionally divided into seven continents and various seas. As people settled and organized the planet, nearly all the land was divided into nations. As of 2013, there are about 196 recognized nations.<ref>[http://geography.about.com/cs/countries/a/numbercountries.htm Number of countries]</ref> An example of how major geographical regions can be broken down is [[Africa]], [[Americas (continent)|America]], [[Antarctica]], [[Asia]], [[Australia]], and [[Europe]].
[[File:Winkel-tripel-projection.jpg|thumb|center|550px|<center>Winkel triple projection map of the Earth's surface</center>]]
{{clear}}
===Hydrosphere===
{{Main|Hydrosphere}}
[[File:Earth elevation histogram 2.svg|thumb|300px|Elevation histogram of the surface of the Earth]]
The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from others in the Solar System. The Earth's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000&nbsp;m. The deepest underwater location is [[Challenger Deep]] of the [[Mariana Trench]] in the [[Pacific Ocean]] with a depth of 10,911.4&nbsp;m.<ref group="note" name=trench_depth/><ref name=kaiko7000/>
 
The mass of the oceans is approximately 1.35{{e|18}}&nbsp;[[metric ton]]s, or about 1/4400 of the total mass of the Earth. The oceans cover an area of {{val|3.618|e=8|ul=km2}} with a mean depth of {{val|3682|ul=m}}, resulting in an estimated volume of {{val|1.332|e=9|ul=km3}}.<ref name=ocean23_2_112/> If all the land on Earth were spread evenly, water would rise to an altitude of more than 2.7&nbsp;km.<ref group=note>The total surface area of the Earth is {{val|5.1|e=8|ul=km2}}. To first approximation, the average depth would be the ratio of the two, or 2.7&nbsp;km.</ref> About 97.5% of the water is saline, while the remaining 2.5% is fresh water. Most fresh water, about 68.7%, is currently ice.<ref name=shiklomanov_et_al_1999/>
 
The average [[salinity]] of the Earth's oceans is about 35&nbsp;grams of salt per kilogram of sea water (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/>
 
===Atmosphere===
{{Main|Atmosphere of Earth}}
[[File:Earthinuvfrommoon.jpg|thumb|right|This is a picture of Earth in ultraviolet light, taken from the surface of the Moon. The day-side (right) reflects a lot of UV light from the Sun, but the night-side (left) shows bands of UV emission from the aurora caused by charged particles.<ref>{{cite web|url=http://science.hq.nasa.gov/kids/imagers/ems/uv.html |title=NASA&nbsp;– Ultraviolet Waves |publisher=Science.hq.nasa.gov |date= |accessdate=2013-05-03}}</ref>]]
 
The [[atmospheric pressure]] on the surface of the Earth averages 101.325&nbsp;[[kPa]], with a [[scale height]] of about 8.5&nbsp;km.<ref name="earth_fact_sheet"/> It is 78% nitrogen and 21% oxygen, with trace amounts of water vapor, carbon dioxide and other gaseous molecules. The height of the [[troposphere]] varies with latitude, ranging between 8&nbsp;km at the poles to 17&nbsp;km at the equator, with some variation resulting from weather and seasonal factors.<ref name=geerts_linacre97/>
 
Earth's biosphere has significantly altered its [[atmosphere]]. [[Oxygen evolution#Oxygen evolution in nature|Oxygenic photosynthesis]] evolved {{val|2.7|u=bya}}, [[oxygen catastrophe|forming]] the primarily nitrogen–oxygen [[atmosphere]] of today.<ref name="NYT-20131003" /> This change enabled the proliferation of [[aerobic organisms]] as well as the formation of the ozone layer which blocks [[ultraviolet]] [[solar radiation]], permitting life on land. Other atmospheric functions important to life on Earth include transporting water vapor, providing useful gases, causing small [[meteor]]s to burn up before they strike the surface, and moderating temperature.<ref name="atmosphere"/> This last phenomenon is known as the [[greenhouse effect]]: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Water vapor, carbon dioxide, methane and ozone are the primary [[greenhouse gas]]es in the Earth's atmosphere. Without this heat-retention effect, the average surface would be −18&nbsp;°C, in contrast to the current +15&nbsp;°C, and life would likely not exist.<ref name="Pidwirny2006_7" />
 
====Weather and climate====
{{Main|Weather|Climate}}
[[File:MODIS Map.jpg|thumb|Satellite [[cloud cover]] image of Earth using [[NASA]]'s [[Moderate-Resolution Imaging Spectroradiometer]]]]
[[File:Pressure ridges Scott Base lrg.jpg|thumb|right|In this scene from Antarctica, Earth's south polar continent, ice ridges contrast with towering clouds]]
The Earth's atmosphere has no definite boundary, slowly becoming thinner and fading into outer space. Three-quarters of the atmosphere's mass is contained within the first 11&nbsp;km of the planet's surface. This lowest layer is called the [[troposphere]]. Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower-density air then rises, and is replaced by cooler, higher-density air. The result is [[atmospheric circulation]] that drives the weather and climate through redistribution of 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 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/>
 
Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and settles to the surface as [[Precipitation (meteorology)|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]], topological features and temperature differences determine the average precipitation that falls in each region.<ref name=hydrologic_cycle/>
 
The amount of solar energy reaching the Earth's decreases with increasing latitude. At higher latitudes the sunlight reaches the surface at lower angles and it must pass through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level decreases by about 0.4&nbsp;°C per degree of latitude away from the equator.<ref name=sadava_heller2006/> The Earth can be subdivided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the [[tropics|tropical]] (or equatorial), [[Subtropics|subtropical]], [[temperate]] and [[Polar region|polar]] climates.<ref name=climate_zones/> Climate can also be classified based on the temperature and precipitation, with the climate regions characterized by fairly uniform air masses. The commonly used [[Köppen climate classification]] system (as modified by [[Wladimir Köppen]]'s student Rudolph Geiger) has five broad groups (humid tropics, [[Desert|arid]], humid middle latitudes, [[Continental climate|continental]] and cold polar), which are further divided into more specific subtypes.<ref name="berger2002" />
 
====Upper atmosphere====
[[File:Full moon partially obscured by atmosphere.jpg|thumb|This view from orbit shows the full Moon partially obscured and deformed by the Earth's atmosphere. ''[[NASA]] image'']]
{{See also|Outer space}}
Above the troposphere, the atmosphere 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 Earth's magnetic 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 100&nbsp;km above the Earth's surface, is a working definition for the boundary between atmosphere and space.<ref name=cordoba2004/>
 
Thermal energy causes some of the molecules at the outer edge of the Earth's atmosphere to increase their velocity to the point where they can [[escape velocity|escape]] from the planet's gravity. This causes a slow but steady [[Atmospheric escape|leakage of the atmosphere into space]]. Because unfixed [[hydrogen]] has a low molecular weight, it can achieve [[escape velocity]] more readily and it leaks into outer space at a greater rate than other gasses.<ref name=jas31_4_1118/> The leakage of hydrogen into space contributes to the pushing of the Earth from an initially [[redox|reducing]] state to its current [[Redox|oxidizing]] one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is believed to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere.<ref name=sci293_5531_839/> Hence the ability of hydrogen to escape from the Earth's atmosphere may have influenced the nature of life that developed on the planet.<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/>
 
===Magnetic field===
[[File:Structure of the magnetosphere mod.svg|thumb|300px|Schematic of Earth's magnetosphere. The [[solar wind]] flows from left to right|alt=Diagram showing the magnetic field lines of the Earth's magnetosphere. The lines are swept back in the anti-solar direction under the influence of the solar wind.]]
{{Main|Earth's magnetic field}}
The [[Earth's magnetic field]] is shaped roughly as a [[magnetic dipole]], with the poles currently located proximate to the planet's geographic poles. At the equator of the magnetic field, the magnetic field strength at the planet's surface is {{nowrap|3.05 × 10<sup>−5</sup> [[Tesla (unit)|T]]}}, with global [[magnetic dipole moment]] of {{nowrap|7.91 × 10<sup>15</sup> T m<sup>3</sup>}}.<ref name=lang2003/> According to [[dynamo theory]], the field is generated within the molten outer core region where heat creates convection motions of conducting materials, generating electric currents. These in turn produce the Earth's magnetic field. The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes [[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 field forms the [[magnetosphere]], which deflects particles in the [[solar wind]]. The sunward edge of the [[bow shock]] is located at about 13 times the radius of the Earth. The collision between the magnetic field and the solar wind forms the [[Van Allen radiation belt]]s, a pair of concentric, [[torus]]-shaped regions of energetic [[charged particle]]s. When the [[plasma (physics)|plasma]] enters the Earth's atmosphere at the magnetic poles, it forms the [[Aurora (astronomy)|aurora]].<ref name=stern2005/>
 
==Orbit and rotation==
===Rotation===
{{Main|Earth's rotation}}
[[File:AxialTiltObliquity.png|thumb|right|280px|Earth's axial tilt (or [[obliquity]]) and its relation to the [[Rotation|rotation axis]] and [[Orbital plane (astronomy)|plane of orbit]]]]
Earth's rotation period relative to the Sun—its mean solar day—is 86,400&nbsp;seconds of mean solar time (86,400.0025&nbsp;[[SI]]&nbsp;seconds).<ref name=aj136_5_1906/> As the Earth's solar day is now slightly longer than it was during the 19th century due to [[tidal acceleration]], each day varies between 0 and 2 [[SI]] [[milliseconds|ms]] longer.<ref name=USNO_TSD/><ref>http://maia.usno.navy.mil/ser7/ser7.dat</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|86,164.098903691 seconds}} of mean solar time (UT1), or {{nowrap |23{{smallsup|h}} 56{{smallsup|m}} 4.098903691{{smallsup|s}}.}}<ref name=IERS/><ref group=note name=Aoki/> Earth's rotation period relative to the [[precession (astronomy)|precessing]] or moving mean vernal [[equinox]], misnamed its ''[[sidereal day]]'', is {{nowrap|86,164.09053083288 seconds}} of mean solar time (UT1) {{nowrap|(23{{smallsup|h}} 56{{smallsup|m}} 4.09053083288{{smallsup|s}})}} {{As of|1982|lc=y}}.<ref name=IERS/> Thus the sidereal day is shorter than the stellar day by about 8.4&nbsp;ms.<ref name=seidelmann1992/> The length of the mean solar day in SI seconds is available from the IERS for the periods 1623–2005<ref name=iers1623/> and 1962–2005.<ref name=iers1962/>
 
Apart from [[meteor]]s within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in the Earth's sky is to the west at a rate of 15°/h = 15'/min. For bodies near the [[celestial equator]], this is equivalent to an apparent diameter of the Sun or Moon every two minutes; from the planet's surface, the apparent sizes of the Sun and the Moon are approximately the same.<ref name=zeilik1998/><ref name=angular/>
 
===Orbit===
{{Main|Earth's orbit}}
Earth orbits the Sun at an average distance of about 150&nbsp;million kilometers every 365.2564 mean solar days, or one [[sidereal year]]. From Earth, this gives an apparent movement of the Sun eastward with respect to the stars at a rate of about 1°/day, 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 time|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 the Earth averages about 29.8&nbsp;km/s (107,000&nbsp;km/h), which is fast enough to travel a distance equal to the planet's diameter, about 12,742&nbsp;km, in seven minutes, and the distance to the Moon, 384,000&nbsp;km, in about 3.5 hours.<ref name="earth fact sheet"/>
 
The Moon revolves with the Earth around a common [[barycentre|barycenter]] every 27.32&nbsp;days relative to the background stars. When combined with the Earth–Moon system's common revolution around the Sun, the period of the [[synodic month]], from new moon to new moon, is 29.53&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 north poles of both the Sun and the Earth, the Earth revolves in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's [[axial tilt|axis is tilted]] some 23.4&nbsp;degrees from the perpendicular to the Earth–Sun plane (the [[ecliptic]]), and the Earth–Moon plane is tilted up to ±5.1&nbsp;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 [[gravity|gravitational]] sphere of influence, of the Earth is about 1.5&nbsp;Gm or 1,500,000&nbsp;km in radius.<ref name=vazquez_etal2006/><ref name=hill_radius group=note/> This is the maximum distance at which the Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit the Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.
 
Earth, along with the Solar System, is situated in the [[Milky Way]] [[galaxy]] and orbits about 28,000&nbsp;[[Light-year|light years]] from the center of the galaxy. It is currently about 20&nbsp;light years above the [[galactic plane]] in the [[Orion Arm|Orion spiral arm]].<ref name=nasa20051201/>
 
===Axial tilt and seasons===
[[File:The Earth and the Moon photographed from Mars orbit.jpg|thumb|225px|right|Earth and Moon from Mars, imaged by [[Mars Reconnaissance Orbiter]]. From space, the Earth can be seen to go through phases similar to the [[lunar phases|phases of the Moon.]]|alt=Black space with crescent Earth at lower left, crescent Moon at upper right, 30% of Earth's apparent diameter; five Earth diameters apparent space between; sunlit from right side]]
{{Main|Axial tilt}}
 
Due to the axial tilt of the Earth, the amount of sunlight reaching any given point on the surface varies over the course of the year. This causes [[season]]al change in climate, with summer in the [[northern hemisphere]] occurring when the North Pole is pointing toward the Sun, and winter taking place when the pole is pointed away. During the summer, the day lasts longer and the Sun climbs higher in the sky. In winter, the climate becomes generally cooler and the days shorter. Above the [[Arctic Circle]], an extreme case is reached where there is no daylight at all for part of the year—a [[polar night]]. In the [[southern hemisphere]] the situation is exactly reversed, with the [[South Pole]] oriented opposite the direction of the North Pole.
 
By astronomical convention, the four seasons are determined by the [[solstice]]s—the point in the orbit of maximum axial tilt toward or away from the Sun—and the [[equinox]]es, when the direction of the tilt and the direction to the Sun are perpendicular. In the northern hemisphere, [[Winter Solstice]] occurs on about December&nbsp;21, [[Summer Solstice]] is near June&nbsp;21, [[Spring Equinox]] is around March&nbsp;20 and [[Autumnal Equinox]] is about September&nbsp;23. In the Southern hemisphere, the situation is reversed, with the Summer and Winter Solstices exchanged and the Spring and Autumnal Equinox dates switched.<ref name=bromberg2008/>
[[File:Earth-Moon system as seen from Saturn (PIA17171).jpg|left|thumb|250px|NASA's [[Cassini spacecraft]] photographs the Earth and [[Moon]] (visible bottom-right) from [[Saturn]] (July 19, 2013).]]
The angle of the Earth's tilt is relatively stable over long periods of time. The tilt does undergo [[nutation]]; a slight, irregular motion with a main period of 18.6&nbsp;years.<ref name=lin2006/> The orientation (rather than the angle) of the Earth's axis also changes over time, [[precession|precessing]] around in a complete circle over each 25,800&nbsp;year cycle; this precession is the reason for the difference between a sidereal year and a [[tropical year]]. Both of these motions are caused by the varying attraction of the Sun and Moon on the Earth's equatorial bulge. From the perspective of the Earth, the poles also migrate a few meters across the surface. This [[polar motion]] has multiple, cyclical components, which collectively are termed [[quasiperiodic motion]]. In addition to an annual component to this motion, there is a 14-month cycle called the [[Chandler wobble]]. The rotational velocity of the Earth also varies in a phenomenon known as length of day variation.<ref name=fisher19960205/>
 
In modern times, Earth's [[perihelion]] occurs around January&nbsp;3, and the [[aphelion]] around July&nbsp;4. These dates change over time due to [[precession (astronomy)|precession]] and other orbital factors, which follow cyclical patterns known as [[Milankovitch cycles]]. The changing Earth–Sun distance causes an increase of about 6.9%<ref name=solar_energy group=note/> in solar energy reaching the Earth at perihelion relative to aphelion. Since the southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, the southern hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. This effect is much less significant than the total 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 name=williams20051230/>
 
==Habitability==
{{See also|Planetary habitability}}
[[File:Pingualuit aerial 2007.jpg|thumb|right|[[Pingualuit crater|This ancient impact crater]], now filled with water, marks Earth's surface]]
A planet that can sustain life is termed habitable, even if life did not originate there. The Earth provides liquid water—an environment where complex organic molecules can assemble and interact, and sufficient energy to sustain [[metabolism]].<ref name=ab2003/> The distance of the Earth from the Sun, as well as its orbital eccentricity, rate of rotation, axial tilt, geological history, sustaining atmosphere and protective magnetic field all contribute to the current climatic conditions at the surface.<ref name=dole1970/>
 
===Biosphere===
{{Main|Biosphere}}
[[File:EilatFringingReef.jpg|thumb|left|Coral reef and beach]]
A planet's life forms are sometimes said to form a "biosphere". The Earth's biosphere is generally believed to have begun [[evolution|evolving]] about {{val|3.5|u=bya}}.<ref name="NYT-20131003" /> The biosphere is divided into a number of [[biome]]s, inhabited by broadly similar plants and animals. On land, biomes are separated primarily by differences in latitude, [[elevation|height above sea level]] and [[humidity]]. Terrestrial [[tundra|biomes]] lying within the [[Arctic Circle|Arctic]] or [[Antarctic Circle]]s, at [[Alpine tundra|high altitudes]] or in [[desert|extremely arid areas]] are relatively barren of plant and animal life; [[Latitudinal gradients in species diversity|species diversity]] reaches a peak in [[tropical rainforest|humid lowlands at equatorial latitudes]].<ref name=amnat163_2_192/>
 
===Evolution of life===
{{Main|Evolutionary history of life}}
[[File:ADN animation.gif|thumb|Computer model of some DNA]]
Highly energetic chemistry is thought to have produced a self-replicating molecule around {{val|4|ul=bya}} and half a billion years later the [[last universal common ancestor|last common ancestor of all life]] existed.<ref name=sa282_6_90/> The development of [[photosynthesis]] allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and formed a layer of [[ozone]] (a form of [[molecular oxygen]] [O<sub>3</sub>]) in the upper atmosphere.<ref name="NYT-20131003">{{cite news |last=Zimmer |first=Carl |authorlink=Carl Zimmer |title=Earth’s Oxygen: A Mystery Easy to Take for Granted |url=http://www.nytimes.com/2013/10/03/science/earths-oxygen-a-mystery-easy-to-take-for-granted.html |date=3 October 2013 |work=[[New York Times]] |accessdate=3 October 2013 }}</ref> The incorporation of smaller cells within larger ones resulted in the [[endosymbiotic theory|development of complex cells]] called [[eukaryotes]].<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 the surface of Earth.<ref name=burton20021129/> The earliest evidences for [[life on Earth]] are [[graphite]] found to be [[Biogenic substance|biogenic]] in  3.7 billion-year-old [[Metasediment|metasedimentary rocks]] discovered in [[Western Greenland]]<ref name="NG-20131208">{{cite web |url =http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2025.html|authors= Yoko Ohtomo, Takeshi Kakegawa, Akizumi Ishida, Toshiro Nagase, Minik T. Rosing| title =Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks |publisher =''[[Nature Geoscience]]''|doi=10.1038/ngeo2025|date=8 December 2013| accessdate =9 Dec 2013 }}</ref> and [[microbial mat]] [[fossils]] found in 3.48 billion-year-old [[sandstone]] discovered in [[Western Australia]].<ref name="AP-20131113">{{cite news |last=Borenstein |first=Seth |title=Oldest fossil found: Meet your microbial mom |url=http://apnews.excite.com/article/20131113/DAA1VSC01.html |date=13 November 2013 |work=[[AP News]] |accessdate=15 November 2013 }}</ref><ref name="AST-20131108">{{cite journal |last1=Noffke |first1=Nora|last2=Christian |first2=Daniel |last3=Wacey |first3=David |last4=Hazen |first4=Robert M. |title=Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia |url=http://online.liebertpub.com/doi/abs/10.1089/ast.2013.1030 |date=8 November 2013 |journal=[[Astrobiology (journal)]] |doi=10.1089/ast.2013.1030 |accessdate=15 November 2013 }}</ref>
 
Since the 1960s, it has been hypothesized that severe [[Glacier|glacial]] action between 750 and {{val|580|u=mya}}, during the [[Neoproterozoic]], covered much of the planet in a sheet of ice. This hypothesis has been termed "[[Snowball Earth]]", and is of particular interest because it preceded the [[Cambrian explosion]], when multicellular life forms began to proliferate.<ref name=kirschvink1992/>
 
Following the Cambrian explosion, about {{val|535|u=mya}}, there have been five [[Extinction event|major mass extinctions]].<ref name=sci215_4539_1501/> The [[Cretaceous–Tertiary extinction event|most recent such event]] was {{val|66|u=mya}}, when an asteroid impact triggered the extinction of the (non-avian) [[dinosaur]]s and other large reptiles, but spared some small animals such as [[mammal]]s, which then resembled [[shrew]]s. Over the past {{val|66|ul=myr}}, mammalian life has diversified, and several million years ago an African ape-like animal such as ''[[Orrorin tugenensis]]'' gained the ability to stand upright.<ref name=gould1994/> This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which allowed the [[Human evolution|evolution of the human race]]. The [[History of agriculture|development of agriculture]], and then [[Civilization#History|civilization]], allowed humans to influence the Earth in a short time span as no other life form had,<ref name=bgsa119_1_140/> affecting both the nature and quantity of other life forms.
 
===Natural resources and land use===
{{Main|Natural resource|Land use}}
 
{| class="wikitable" style="float:right; margin-left:1em;"
|+ Estimated human land use, 2000<ref name="Lambina2011"/>
|-
!Land use
!Mha
|-
| Cropland
|style="text-align:center"| 1,510–1,611
|-
| Pastures
|style="text-align:center"| 2,500–3,410
|-
| Natural forests
|style="text-align:center"| 3,143–3,871
|-
| Planted forests
|style="text-align:center"| 126–215
|-
| Urban areas
|style="text-align:center"| 66–351
|-
| Unused, productive land
|style="text-align:center"| 356–445
|}
The Earth provides resources that are exploitable by humans for useful purposes. Some of these are [[non-renewable resources]], such as [[fossil fuel|mineral fuels]], that are difficult to replenish on a short time scale.
 
Large deposits of [[fossil fuel]]s are obtained from the Earth's crust, consisting of coal, petroleum, [[natural gas]] and [[methane clathrate]]. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed in Earth's crust through a process of [[Ore genesis]], resulting from actions of erosion and plate tectonics.<ref name=mnpl_utx2006/> These bodies form concentrated sources for many metals and other useful [[chemical element|elements]].
 
The Earth's biosphere produces many useful biological products for humans, including (but far from limited to) [[food]], wood, [[pharmaceutical]]s, oxygen, and the recycling of many organic wastes. The land-based [[ecosystem]] depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land.<ref name=science299_5607_673/> In 1980, 5,053 [[Hectare|Mha]] of the Earth's land surface consisted of forest and woodlands, 6,788 Mha were grasslands and pasture, and 1,501 Mha was cultivated as croplands.<ref name="Turner1990"/> The estimated amount of irrigated land in 1993 was {{convert|2481250|km2}}.<ref name=cia/> Humans also live on the land by using [[building material]]s to construct shelters.
 
===Natural and environmental hazards===
[[File:Pavlof2014iss.jpg|thumb|right|320px|<Center>A volcano ejecting hot ash into the atmosphere</center>]]
Large areas of the Earth's surface are subject to extreme weather such as tropical [[cyclone]]s, [[hurricane]]s, or [[typhoon]]s that dominate life in those areas. From 1980 to 2000, these events caused an average of 11,800 deaths per year.<ref name=walsh2008/> Many places are subject to [[earthquake]]s, [[landslide]]s, [[tsunami]]s, [[volcano|volcanic eruptions]], [[tornado]]es, [[sinkhole]]s, [[blizzard]]s, floods, droughts, [[wildfire]]s, and other calamities and disasters.
 
Many localized areas are subject to human-made [[pollution]] of the air and water, [[acid rain]] and toxic substances, loss of vegetation ([[overgrazing]], [[deforestation]], [[desertification]]), loss of wildlife, species extinction, [[soils retrogression and degradation|soil degradation]], soil depletion, erosion, and introduction of [[invasive species]].
 
According to the [[United Nations]], a scientific consensus exists linking human activities to [[global warming]] due to industrial carbon dioxide emissions. This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather and a [[Sea level rise|global rise in average sea levels]].<ref name=un20070202/>
 
===Human geography===
{{Main|Human geography|World}}
 
{{multiple image
| align    = right
| direction = vertical
| width    = 320
 
| image1    = Continents vide couleurs.png
| alt1      =
| caption1  = The 7 continents of Earth:<ref name=NatlGeo>[http://www.nationalgeographic.com/xpeditions/atlas/index.html?Parent=world&Mode=d&SubMode=w World], ''[[National Geographic Society|National Geographic]]&nbsp;– [http://www.nationalgeographic.com/xpeditions/ Xpeditions Atlas].'' 2006. Washington, DC: National Geographic Society.</ref> {{nowrap|{{colorbox|#0c0}} [[North America]],}} {{nowrap|{{colorbox|green}} [[South America]],}} {{nowrap|{{colorbox|#0040ff}} [[Antarctica]],}} {{nowrap|{{colorbox|#fed52e}} [[Africa]],}} {{nowrap|{{colorbox|#c10000}} [[Europe]],}} {{nowrap|{{colorbox|#f33e01}} [[Asia]],}} {{nowrap|{{colorbox|#c04080}} [[Australia (continent)|Australia]]}}
 
| image2    = Earthlights dmsp.jpg
| alt2      =
| caption2  = The Earth at night in 2000, a composite of [[Defense Meteorological Satellite Program|DMSP]]/OLS ground illumination data on a simulated night-time image of the world
}}
 
[[Cartography]], the study and practice of map making, and vicariously [[geography]], have historically been the disciplines devoted to depicting the Earth. [[Surveying]], the determination of locations and distances, and to a lesser extent [[navigation]], the determination of position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information.
 
Earth has reached approximately seven billion human inhabitants as of October 31, 2011.<ref>{{cite web|url=http://news.yahoo.com/various-7-billionth-babies-celebrated-worldwide-064439018.html|title=Various '7 billionth' babies celebrated worldwide|accessdate=2011-10-31}}</ref> Projections indicate that the [[world population|world's human population]] will reach 9.2&nbsp;billion in 2050.<ref name=un2006/> Most of the growth is expected to take place in [[developing nations]]. Human [[population density]] varies widely around the world, but a majority live in [[Asia]]. By 2020, 60% of the world's population is expected to be living in urban, rather than rural, areas.<ref name=prb2007/>
 
It is estimated that only one-eighth of the surface of the Earth is suitable for humans to live on—three-quarters is covered by oceans, and half of the land area is either desert (14%),<ref name=hessd4_439/> high mountains (27%),<ref name=biodiv/> or other less suitable terrain. The northernmost permanent settlement in the world is [[Alert, Nunavut|Alert]], on [[Ellesmere Island]] in [[Nunavut]], Canada.<ref name=cfsa2006/> (82°28′N) The southernmost is the [[Amundsen-Scott South Pole Station]], in Antarctica, almost exactly at the South Pole. (90°S)
 
Independent sovereign nations claim the planet's entire land surface, except for some parts of Antarctica and the odd [[Terra nullius|unclaimed area]] of [[Bir Tawil]] between Egypt and Sudan. As of 2013, there are [[List of sovereign states|206 sovereign states]], including the 193 [[United Nations member states]]. In addition, there are 59 [[Dependent territory|dependent territories]], and a number of [[List of autonomous areas by country|autonomous areas]], [[List of territorial disputes|territories under dispute]] and other entities.<ref name=cia /> Historically, Earth has never had a [[sovereignty|sovereign]] government with authority over the entire globe, although a number of nation-states have striven for [[Hyperpower|world domination]] and failed.<ref name=kennedy1989/>
 
The [[United Nations]] is a worldwide [[international organization|intergovernmental organization]] that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict.<ref name=uncharter/> The U.N. serves primarily as a forum for international diplomacy and [[international law]]. When the consensus of the membership permits, it provides a mechanism for armed intervention.<ref name=un_int_law/>
[[File:AS8-13-2329.jpg|thumb|right|The first photograph ever taken by astronauts of an "[[Earthrise]]", from [[Apollo 8]]]]
The first human to orbit the Earth was [[Yuri Gagarin]] on April 12, 1961.<ref name=kuhn2006/> In total, about 487 people have visited [[outer space]] and reached Earth orbit as of July 30, 2010, and, of these, [[Apollo program|twelve]] have walked on the Moon.<ref name=ellis2004/><ref name=shayler_vis2005/><ref name=wade2008/> Normally the only humans in space are those on the [[International Space Station]]. The station's crew, currently six people, is usually replaced every six months.<ref name=nasa_rg_iss2007/> The furthest humans have travelled from Earth is 400,171&nbsp;km, achieved during the 1970 [[Apollo 13]] mission.<ref name=cramb2007/>
 
==Cultural and historical viewpoint==
{{Main|Earth in culture}}
The standard astronomical symbol of the Earth consists of a cross circumscribed by a circle.<ref name=liungman2004/>
 
Unlike the rest of the planets in the Solar System, humankind did not begin to view the Earth as a moving object in orbit around the Sun until the 16th century.<ref name=arnett20060716/> Earth has often been personified as a deity, in particular a goddess. In many cultures a [[mother goddess]] is also portrayed as a [[fertility deity]]. [[Creation myth]]s in many religions recall a story involving the creation of the Earth by a supernatural deity or deities. A variety of religious groups, often associated with [[Fundamentalism|fundamentalist]] branches of Protestantism<ref name=Dutch2002/> or Islam,<ref name=edis2003/> assert that their [[Hermeneutics|interpretations]] of these creation myths in [[Religious text|sacred texts]] are [[Creation science|literal truth]] and should be considered alongside or replace conventional scientific accounts of the formation of the Earth and the origin and development of life.<ref name=jge53_3_319/> Such assertions are opposed by the [[scientific community]]<ref name=arghg4_143/><ref name=sec_nap2008/> and by other religious groups.<ref name=jrst43_4_419/><ref name=frye1983/><ref name=nathist106_2_16/> A prominent example is the [[creation–evolution controversy]].
 
In the past, there were varying levels of belief in a [[flat Earth]],<ref name=russell1997/> but this was displaced by [[spherical Earth]], a concept that has been credited to [[Pythagoras]] (6th century BC).<ref name=jacobs19980201/> [[Culture|Human cultures]] have developed many views of the planet, including its [[Anthropomorphism|personification]] as a planetary [[deity]], its shape [[flat Earth|as flat]], its position as [[Geocentric model|the center of the universe]], and in the modern [[Gaia hypothesis|Gaia Principle]], as a single, self-regulating organism in its own right.
 
==Chronology==
===Formation===
{{Main|History of the Earth}}
[[File:Archivo 362.png|thumb|350px|Artist's impression of the birth of the Solar System]]The earliest material found in the Solar System is dated to {{val|4.5672|0.0006|ul=bya}};<ref name=bowring_housch1995/> therefore, it is inferred that the Earth must have been formed by [[accretion (astrophysics)|accretion]] around this time. By {{val|4.54|0.04|u=bya}}<ref name="age_earth1" /> the primordial Earth had formed. The [[formation and evolution of the Solar System]] bodies occurred in tandem 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 in tandem with the star. A nebula contains gas, ice grains and [[Cosmic dust|dust]] (including [[primordial nuclides]]). In [[nebular theory]] [[planetesimal]]s commence forming as [[Granular material#Granular gases|particulate]] accrues by [[cohesion (geology)|cohesive clumping]] and then by gravity. The assembly of the primordial Earth proceeded for 10–{{val|20|ul=myr}}.<ref name=nature418_6901_949/> The Moon formed shortly thereafter, about {{val|4.53|u=bya}}.<ref name=science310_5754_1671/>
 
The Moon's formation remains debated. The [[working hypothesis]] is that it formed by [[Accretion (astrophysics)|accretion]] from material loosed from the Earth after a Mars-sized object dubbed [[Theia (planet)|Theia]] [[giant impact hypothesis|impacted]] with Earth.<ref name=reilly20091022/> The model, however, is not self-consistent. In this scenario, the mass of Theia is 10% of the Earth's mass,<ref name=canup_asphaug2001a/> it impacts with the Earth in a glancing blow,<ref name=canup_asphaug2001b/> and some of its mass merges with the Earth. Between approximately 3.8 and {{val|4.1|u=bya}}, numerous [[asteroid]] impacts during the [[Late Heavy Bombardment]] caused significant changes to the greater surface environment of the Moon, and by inference, to the Earth.
 
===Geological history===
{{Main|Geological history of Earth}}
[[File:Ap 16 view of Earth during TLC.jpg|thumb|left|Earth from Apollo 16 during the trans-lunar coast]]
Earth's atmosphere and oceans formed by [[Volcano|volcanic]] activity and [[outgassing]] that included [[water vapor]]. The [[origin of the world's oceans]] was condensation augmented by water and ice delivered by [[asteroid]]s, [[Protoplanet|proto-planets]], and [[comet]]s.<ref name="watersource"/> In [[faint young Sun paradox|this model]], atmospheric "[[greenhouse gas]]es" kept the oceans from freezing while the newly forming Sun was only at 70% [[solar luminosity|luminosity]].<ref name=asp2002/> By {{val|3.5|u=bya}}, the [[Earth's magnetic field]] was established, which helped prevent the atmosphere from being stripped away by the [[solar wind]].<ref name=physorg20100304/>
A [[Crust (geology)|crust]] formed when the molten outer layer of the planet Earth cooled [[Phase transition|to form]] a solid as the accumulated water vapor began to act in the atmosphere. The two models<ref name=williams_santosh2004/> that explain land mass propose either a steady growth to the present-day forms<ref name=science164_1229/> or, more likely, a rapid growth<ref name=tp322_19/> early in Earth history<ref name=rg6_175/> followed by a long-term steady continental area.<ref name=science310_5756_1947/><ref name=jaes23_799/><ref name=ajes38_613/> Continents formed by [[plate tectonics]], a process ultimately driven by the continuous loss of heat from the earth's interior. On [[Geologic time scale|time scales]] lasting hundreds of millions of years, the [[supercontinent]]s have formed and broken up three times. Roughly {{val|750|ul=mya}} (million years ago), one of the earliest known supercontinents, [[Rodinia]], began to break apart. The continents later recombined to form [[Pannotia]], 600–{{val|540|u=mya}}, then finally [[Pangaea]], which also broke apart {{val|180|u=mya}}.<ref name=as92_324/>
 
The present pattern of [[ice age]]s began about {{val|40|u=mya}} and then intensified during the [[Pleistocene]] about {{val|3|u=mya}}. High-[[latitude]] regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–{{val|100000|u=years}}. The last continental glaciation ended 10,000&nbsp;years ago.<ref name=psc/>
 
===Predicted future===
{{Main|Future of the Earth}}
Estimates on how much longer the planet will be able to continue to support life range from {{Nowrap|500 million years (myr)}}, to as long as {{Nowrap|2.3 billion years (byr)}}.<ref name="britt2000" /><ref name=carrington /><ref name="pnas1_24_9576" /> The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium at the Sun's core, the [[Solar luminosity|star's total luminosity]] will slowly increase. The luminosity of the Sun will grow by 10% over the next {{val|1.1|ul=byr}} and by 40% over the next {{val|3.5|u=byr}}.<ref name="sun_future"/> Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the loss of the planet's oceans.<ref name=icarus74_472/>
 
The Earth's increasing surface temperature will accelerate the [[inorganic]] [[Carbon cycle|CO<sub>2</sub> cycle]], reducing its concentration to levels lethally low for plants ({{val|10|ul=ppm}} for [[C4 carbon fixation|C4 photosynthesis]]) in approximately 500-{{val|900|u=myr}}.<ref name="britt2000" /> The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years.<ref name=ward_brownlee2002/> After another billion years all surface water will have disappeared<ref name=carrington/> and the mean global temperature will reach {{val|70|ul=degC}}<ref name=ward_brownlee2002/> ({{val|158|ul=degF}}). The Earth is expected to be effectively habitable for about another {{val|500|u=myr}} from that point,<ref name="britt2000"/> although this may be extended up to {{val|2.3|u=byr}} if the nitrogen is removed from the atmosphere.<ref name=pnas1_24_9576/> Even if the Sun were eternal and stable, 27% of the water in the modern oceans will descend to the [[Mantle (geology)|mantle]] in one billion years, due to reduced steam venting from mid-ocean ridges.<ref name=hess5_4_569/>
[[File:Solar Life Cycle.svg|thumb|700px|center|alt=14 billion year timeline showing Sun's present age at {{val|4.6|ul=byr}}; from {{val|6|u=byr}} Sun gradually warming, becoming a red dwarf at {{val|10|u=byr}}, "soon" followed by its transformation into a white dwarf star|The life cycle of the Sun]]
The Sun, as part of its [[stellar evolution|evolution]], will become a [[red giant]] in about {{val|5|u=byr}}. Models predict that the Sun will expand out to about 250 times its present radius, roughly {{convert|1|AU|km| lk=off|abbr=on}}.<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, the Earth will move to an orbit {{convert|1.7|AU|km| abbr=on}} from the Sun, when the star reaches its maximum radius. The planet was, therefore, initially expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though most, if not all, remaining life would have been destroyed by the Sun's increased luminosity (peaking at about 5,000 times its present level).<ref name="sun_future" /> A 2008 simulation indicates that the Earth's orbit will decay due to [[Tidal acceleration|tidal effects]] and drag, causing it to enter the red giant Sun's atmosphere and be vaporized.<ref name="sun_future_schroder" /> After that, the Sun's core will collapse into a [[white dwarf]], as its outer layers are ejected into space as a [[planetary nebula]]. The matter that once made up the Earth will be released into interstellar space, where it may one day become incorporated into a new generation of planets and other celestial bodies.
{{See also|Risks to civilization, humans, and planet Earth}}
 
==Moon==
{| class="wikitable" style="float: right; margin-left: 0.5em;"
|+ '''Characteristics'''
|-
| '''Diameter''' || 3,474.8&nbsp;km
|-
| '''Mass''' || 7.349{{e|22}}&nbsp;kg
|-
| '''[[Semi-major axis]]''' || 384,400&nbsp;km
|-
| '''Orbital period''' || {{nowrap|27 d 7 h 43.7 m}}
|}
[[File:Earth-Moon.svg|thumb|250px|Details of the Earth–Moon system. Besides the radius of each object, the radius to the Earth–Moon [[barycentre|barycenter]] is shown. Photos from [http://visibleearth.nasa.gov/view_set.php?categoryID=2363 NASA]. Data from [http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html NASA]. The Moon's axis is located by [[Cassini's Laws|Cassini's third law]].]]
 
[[File:FullMoon2010.jpg|thumb|left|[[Full moon]] as seen from Earth's [[northern hemisphere]]]]
{{Main|Moon}}
The Moon is a relatively large, [[Terrestrial planet|terrestrial]], planet-like satellite, with a diameter about one-quarter of the Earth's. It is the largest moon in the Solar System relative to the size of its planet, although [[Charon (moon)|Charon]] is larger relative to the [[dwarf planet]] [[Pluto]]. The natural satellites orbiting other planets are called "moons" after Earth's Moon.
 
The gravitational attraction between the Earth and Moon causes [[tides]] on Earth. The same effect on the Moon has led to its [[tidal locking]]: its rotation period is the same as the time it takes to orbit the Earth. As a result, it always presents the same face to the planet. As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the [[lunar phase]]s; the dark part of the face is separated from the light part by the [[terminator (solar)|solar terminator]].
 
Due to their [[Tidal acceleration|tidal interaction]], the Moon recedes from Earth at the rate of approximately 38&nbsp;mm a year. Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23&nbsp;[[Microsecond|µs]] a year—add up to significant changes.<ref name=espenak_meeus20070207/> During the [[Devonian]] period, for example, (approximately {{val|410|ul=mya}}) there were 400 days in a year, with each day lasting 21.8 hours.<ref name=hannu_poropudas19911216/>
 
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 believe that without this stabilization against the [[torque]]s applied by the Sun and planets to the Earth's equatorial bulge, the rotational axis might be chaotically unstable, exhibiting chaotic changes over millions of years, as appears to be the case for Mars.<ref name=nature410_6830_773/>
 
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 eclipse]]s to occur on Earth.
 
The most widely accepted theory of the Moon's origin, the [[Giant impact hypothesis|giant impact theory]], states that it formed from the collision of a Mars-size [[protoplanet]] called [[Theia (planet)|Theia]] with the early Earth. This hypothesis explains (among other things) the Moon's relative lack of iron and volatile elements, and the fact that its composition is nearly identical to that of the Earth's crust.<ref name=nature412_708/>
 
[[File:Earth Moon Scale.jpg|thumb|center|800px|A scale representation of the relative sizes of, and average distance between, Earth and the Moon]]
 
==Asteroids and artificial satellites==
[[Image:STS-130 Endeavour flyaround 5.jpg|thumb|The [[International Space Station]] is an artificial satellite that orbits Earth.]]
Earth has at least five [[Quasi-satellite|co-orbital asteroids]], including [[3753 Cruithne]] and {{mpl|2002 AA|29}}.<ref name=whitehouse20021021/><ref name=christou_asher2011/> A [[trojan asteroid]] companion, {{mpl|2010 TK|7}}, is librating around the leading [[Lagrange point|Lagrange triangular point]], L4, of Earth in [[Earth's orbit]] around the [[Sun]].<ref name=Connors/><ref name=Choi/>
 
{{As of|2011}}, there are 931 operational, man-made [[satellite]]s orbiting the Earth.<ref name=ucs/> There are also inoperative satellites and over 300,000 pieces of [[space debris]]. Earth's largest artificial satellite is the [[International Space Station]].
 
==Comparisons==
{{gallery
|lines=4
|align=center
|width=300
|height=200
|File:Terrestrial planets size comparison.png
  |Size comparison of [[Mercury (planet)|Mercury]], [[Venus]], Earth and [[Mars]]
|File:Enceladus moon to scale-PIA07724.jpg
  |A size comparison of Earth's [[British Isles]] to a moon of the planet Saturn.
|File:PIA17046 - Voyager 1 Goes Interstellar.jpg
  |The location of Earth on a [[logarithmic]] scale from left right, with observed and predicted features (from 1 to one million [[astronomical unit|AU]]). The location of Earth's most distant probe is also noted.
}}
 
==From space==
[[File:View of Earth from MESSENGER.jpg|thumb|left|600px|<center>Earth as seen by Messenger</center>]]
{{Clear}}
 
==See also==
{{Wikipedia books|1=Earth|3=Solar System}}
* [[Discovery and exploration of the Solar System]]
* [[Sun]]
 
==Notes==
{{Reflist|30em|group=note|refs=
<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 the Earth's perihelion and aphelion is exactly 5 million kilometers (accurate to five [[significant figures]]).</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=asc_node>The reference lists the longitude of the ascending node as −11.26064°, which is equivalent to 348.73936° by the fact that any angle is equal to itself plus 360°.</ref>
 
<ref name=arg_peri>The reference lists the [[longitude of periapsis|longitude of perihelion]], which is the sum of the longitude of the ascending node and the argument of perihelion. That is, 114.20783° + (−11.26064°) = 102.94719°.</ref>
 
<ref name=sidereal_solar>The number of solar days is one less than the number of [[sidereal day]]s because the orbital motion of the Earth about the Sun causes one additional revolution of the planet about its axis.</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] datasets, extreme values for coverage of lakes and streams are 0.6% and 1.0% of the Earth's surface. The ice shields of [[Antarctica]] and [[Greenland]] are counted as land, even though much of the rock which supports them lies below sea level.</ref>
 
<ref name=jaes41_3_379>Including the [[Somali Plate]], which is currently in the process of formation 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=trench_depth>This is the measurement taken by the vessel ''[[Kaikō]]'' in March 1995 and is believed to be the most accurate measurement to date. See the [[Challenger Deep]] article for more details.</ref>
 
<ref name=Aoki>Aoki, the ultimate source of these figures, uses the term "seconds of UT1" instead of "seconds of mean solar time".—{{cite journal|last=Seidelmann|first=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=hill_radius>For the Earth, the [[Hill radius]] is <math>R_H = a\left ( \frac{m}{3M} \right )^{\frac{1}{3}}</math>, where ''m'' is the mass of the Earth, ''a'' is an Astronomical Unit, and ''M'' is the mass of the Sun. So the radius in A.U. is about <math>\left ( \frac{1}{3 \cdot 332,946} \right )^{\frac{1}{3}} = 0.01</math>.</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% the energy at aphelion.</ref>
 
}}
 
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<ref name="WGS-84-2">{{cite web | first1=Sigurd | last1=Humerfelt | date=October 26, 2010 | title=How WGS 84 defines Earth | url=http://home.online.no/~sigurdhu/WGS84_Eng.html | accessdate=2011-04-29 }}</ref>
 
<ref name="yoder12">{{cite book|last1=Yoder|first1=Charles F.|editor=T. J. Ahrens|year=1995|title=Global Earth Physics: A Handbook of Physical Constants|publisher=American Geophysical Union|location=Washington|url=http://www.agu.org/reference/gephys.html|archiveurl=http://replay.waybackmachine.org/20090421092502/http://www.agu.org/reference/gephys.html|archivedate=2007-03-08|accessdate=2007-03-17|isbn=0-87590-851-9 |page=12}}</ref>
 
<ref name=kinver20091210>{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/8406839.stm|title=Global average temperature may hit record level in 2010|last1=Kinver|first1=Mark|date=December 10, 2009|work=[[BBC Online]]|accessdate=2010-04-22}}</ref>
 
<ref name="Pidwirny 2006_8">{{cite journal|last1=Pidwirny|first1=Michael|date=2006-02-02|title=Surface area of our planet covered by oceans and continents.(Table 8o-1)|publisher=University of British Columbia, Okanagan|url=http://www.physicalgeography.net/fundamentals/8o.html|accessdate=2007-11-26}}</ref>
 
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<ref name="age_earth1">See:
* {{cite book|first1=G.B.|last1=Dalrymple|year=1991|title=The Age of the Earth|publisher=Stanford University Press|location=California|isbn=0-8047-1569-6}}
* {{cite web|last=Newman|first=William L.|date=2007-07-09|url=http://pubs.usgs.gov/gip/geotime/age.html|title=Age of the Earth|publisher=Publications Services, USGS|accessdate=2007-09-20}}
* {{cite journal|last1=Dalrymple|first1=G. Brent|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|accessdate=2007-09-20|doi = 10.1144/GSL.SP.2001.190.01.14|bibcode = 2001GSLSP.190..205D }}
* {{cite web|last1=Stassen|first1=Chris|date=2005-09-10|url=http://www.talkorigins.org/faqs/faq-age-of-earth.html|title=The Age of the Earth|publisher=[[TalkOrigins Archive]]|accessdate=2008-12-30}}
</ref>
 
<ref name="Harrison 2002">{{cite book|first1=Roy M.|last1=Harrison|last2=Hester|first2=Ronald E.|year=2002|title=Causes and Environmental Implications of Increased UV-B Radiation|publisher=Royal Society of Chemistry|isbn=0-85404-265-2}}</ref>
 
<ref name=standish_williams_iau>{{cite web|last1=Standish|first1=E. Myles|last2=Williams|first2=James C.|title=Orbital Ephemerides of the Sun, Moon, and Planets|publisher=International Astronomical Union Commission 4: (Ephemerides)|url=http://iau-comm4.jpl.nasa.gov/XSChap8.pdf|format=PDF|accessdate=2010-04-03}} See table 8.10.2. Calculation based upon 1 AU = 149,597,870,700(3) m.</ref>
 
<ref name=carrington>{{cite news|first1=Damian|last1=Carrington|title=Date set for desert Earth|publisher=BBC News|date=2000-02-21|url=http://news.bbc.co.uk/1/hi/sci/tech/specials/washington_2000/649913.stm|accessdate=2007-03-31}}</ref>
 
<ref name=yoder1995>{{cite book|last1=Yoder|first1=Charles F.|editor=T. J. Ahrens|year=1995|title=Global Earth Physics: A Handbook of Physical Constants|publisher=American Geophysical Union|location=Washington|url=http://replay.waybackmachine.org/20090421092502/http://www.agu.org/reference/gephys.html|accessdate=2007-03-17|isbn=0-87590-851-9 |page=8}}</ref>
 
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<ref name=nature418_6901_949>{{cite journal|last1=Yin|first1=Qingzhu|title=A short timescale for terrestrial planet formation from Hf-W chronometry of meteorites|journal=Nature|year=2002|volume=418|issue=6901|pages=949–952|doi=10.1038/nature00995|pmid=12198540|last2=Jacobsen|first2=S. B.|last3=Yamashita|first3=K.|last4=Blichert-Toft|first4=J.|last5=Télouk|first5=P.|last6=Albarède|first6=F.|bibcode = 2002Natur.418..949Y }}</ref>
 
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<ref name=reilly20091022>{{cite news|first1=Michael|last1=Reilly|date=October 22, 2009|title=Controversial Moon Origin Theory Rewrites History|url=http://news.discovery.com/space/moon-earth-formation.html|accessdate=2010-01-30}}</ref>
 
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<ref name="sun_future_schroder">{{cite journal|first1=K.-P.|last1=Schröder|last2=Connon Smith|first2=Robert|year=2008|title=Distant future of the Sun and Earth revisited|doi=10.1111/j.1365-2966.2008.13022.x|journal=Monthly Notices of the Royal Astronomical Society|arxiv=0801.4031|volume=386|issue=1|page=155|bibcode=2008MNRAS.386..155S}}<br>See also {{cite news|first=Jason|last=Palmer|url=http://space.newscientist.com/article/dn13369-hope-dims-that-earth-will-survive-suns-death.html?feedId=online-news_rss20|title=Hope dims that Earth will survive Sun's death|date=2008-02-22|work=NewScientist.com news service|accessdate=2008-03-24}}</ref>
 
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<ref name="ngdc2006">{{cite web|last1=Sandwell|first1=D. T.|last2=Smith|first2=W. H. F.|date=2006-07-07|url=http://www.ngdc.noaa.gov/mgg/bathymetry/predicted/explore.HTML|title=Exploring the Ocean Basins with Satellite Altimeter Data|publisher=NOAA/NGDC|accessdate=2007-04-21}}</ref>
 
<ref name=nist_length2000>{{cite web|last1=Mohr|first1=P. J.|last2=Taylor|first2=B. N.|date=October 2000|url=http://physics.nist.gov/cuu/Units/meter.html|title=Unit of length (meter)|work=NIST Reference on Constants, Units, and Uncertainty|publisher=NIST Physics Laboratory|accessdate=2007-04-23}}</ref>
 
<ref name=wpba2001>{{cite web|author=Staff|date=November 2001|url=http://www.wpa-pool.com/index.asp?content=rules_spec|title=WPA Tournament Table & Equipment Specifications|publisher=World Pool-Billiards Association|accessdate=2007-03-10}}</ref>
 
<ref name=ps20_5_16>{{cite journal|last1=Senne|first1=Joseph H.|title=Did Edmund Hillary Climb the Wrong Mountain|journal=Professional Surveyor|year=2000|volume=20|issue=5|pages=16–21}}</ref>
 
<ref name=lancet365_9462_831>{{cite journal|last1=Sharp|first1=David|title=Chimborazo and the old kilogram|journal=The Lancet|date=2005-03-05|volume=365|issue=9462|pages=831–832|doi=10.1016/S0140-6736(05)71021-7|pmid=15752514}}</ref>
 
<ref name=tall_tales>{{cite web|url=http://www.abc.net.au/science/k2/moments/s1086384.htm|title=Tall Tales about Highest Peaks|publisher=Australian Broadcasting Corporation|accessdate=2008-12-29}}</ref>
 
<ref name=brown_mussett1981>{{cite book|last1=Brown|first1=Geoff C.|last2=Mussett|first2=Alan E.|title=The Inaccessible Earth|edition=2nd|year=1981|page=166|publisher=Taylor & Francis|isbn=0-04-550028-2}} Note: After Ronov and Yaroshevsky (1969).</ref>
 
<ref name=pnas71_12_6973>{{cite journal|last1=Morgan|first1=J. W.|last2=Anders|first2=E.|title=Chemical composition of Earth, Venus, and Mercury|journal=Proceedings of the National Academy of Sciences|year=1980|volume=77|issue=12|pages=6973–6977|doi=10.1073/pnas.77.12.6973|pmid=16592930|pmc=350422|bibcode = 1980PNAS...77.6973M }}</ref>
 
<ref name=tanimoto_ahrens1995>{{cite book|first1=Toshiro|last1=Tanimoto|editor=Thomas J. Ahrens|year=1995|title=Crustal Structure of the Earth|booktitle=Global Earth Physics: A Handbook of Physical Constants|publisher=American Geophysical Union|location=Washington, DC|isbn=0-87590-851-9|url=http://www.agu.org/reference/gephys/15_tanimoto.pdf|archiveurl=https://web.archive.org/web/20061016194153/http://www.agu.org/reference/gephys/15_tanimoto.pdf|archivedate=2006-10-16|format=PDF|accessdate=2007-02-03}}</ref>
 
<ref name=science309_5739_1313>{{cite journal|last1=Kerr|first1=Richard A.|title=Earth's Inner Core Is Running a Tad Faster Than the Rest of the Planet|journal=Science|date=2005-09-26|volume=309|issue=5739|page=1313|doi=10.1126/science.309.5739.1313a|pmid=16123276}}</ref>
 
<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 }}</ref>
 
<ref name=robertson2001>{{cite web|last1=Robertson|first1=Eugene C.|date=2001-07-26|url=http://pubs.usgs.gov/gip/interior/|title=The Interior of the Earth|publisher=USGS|accessdate=2007-03-24}}</ref>
 
<ref name="turcotte">{{cite book|last1=Turcotte|first1=D. L.|last2=Schubert|first2=G.|title=Geodynamics|publisher=Cambridge University Press|location=Cambridge, England, UK| year=2002|edition=2|pages=136–137|chapter=4|isbn=978-0-521-66624-4}}</ref>
 
<ref name=sanders20031210>{{cite news|first1=Robert|last1=Sanders|title=Radioactive potassium may be major heat source in Earth's core|publisher=UC Berkeley News|date=2003-12-10|url=http://www.berkeley.edu/news/media/releases/2003/12/10_heat.shtml|accessdate=2007-02-28}}</ref>
 
<ref name=ptrsl360_1795_1227>{{cite journal|last1=Alfè|first1=D.|last2=Gillan|first2=M. J.|last3=Vocadlo|first3=L.|last4=Brodholt|first4=J.|last5=Price|first5=G. D.|title=The ''ab initio'' simulation of the Earth's core|journal= Philosophical Transactions of the Royal Society|year=2002|volume=360|issue=1795|pages=1227–1244|url=http://chianti.geol.ucl.ac.uk/~dario/pubblicazioni/PTRSA2002.pdf|format=PDF|accessdate=2007-02-28|doi=10.1098/rsta.2002.0992|bibcode = 2002RSPTA.360.1227A }}</ref>
 
<ref name=epsl121_1>{{cite journal|last1=Vlaar|first1=N|title=Cooling of the Earth in the Archaean: Consequences of pressure-release melting in a hotter mantle|year=1994|journal=Earth and Planetary Science Letters|volume=121|issue=1–2|page=1|doi=10.1016/0012-821X(94)90028-0|coauthors=Vankeken, P.; Vandenberg, A. |url=http://www.geo.lsa.umich.edu/~keken/papers/Vlaar_EPSL94.pdf |format=PDF|bibcode=1994E&PSL.121....1V}}</ref>
 
<ref name="T&S 137">{{cite book|last1=Turcotte|first1=D. L.|last2=Schubert|first2=G.|title=Geodynamics|publisher=Cambridge University Press|location=Cambridge, England, UK|year=2002|edition=2|page=137|chapter=4|isbn=978-0-521-66624-4}}</ref>
 
<ref name="heat loss">{{cite journal|doi=10.1029/JB086iB12p11535|title=Oceans and Continents: Similarities and Differences in the Mechanisms of Heat Loss|year=1981|last1=Sclater|first1=John G|journal=Journal of Geophysical Research|volume=86|issue=B12 |page=11535|coauthors=Parsons, Barry; Jaupart, Claude|bibcode=1981JGR....8611535S}}</ref>
 
<ref name=science246_4926_103>{{cite journal|last1=Richards|first1=M. A.|last2=Duncan|first2=R. A.|last3=Courtillot|first3=V. E.|title=Flood Basalts and Hot-Spot Tracks: Plume Heads and Tails|journal=Science|year=1989|volume=246|issue=4926|pages=103–107|bibcode=1989Sci...246..103R|doi=10.1126/science.246.4926.103|pmid=17837768}}</ref>
 
<ref name=brown_wohletz2005>{{cite web|last1=Brown|first1=W. K.|last2=Wohletz|first2=K. H.|year=2005|url=http://www.ees1.lanl.gov/Wohletz/SFT-Tectonics.htm|title=SFT and the Earth's Tectonic Plates|publisher=Los Alamos National Laboratory|accessdate=2007-03-02}}</ref>
 
<ref name=kious_tilling1999>{{cite web|last1=Kious|first1=W. J.|last2=Tilling|first2=R. I.|date=1999-05-05|url=http://pubs.usgs.gov/gip/dynamic/understanding.html|title=Understanding plate motions|publisher=USGS|accessdate=2007-03-02}}</ref>
 
<ref name=seligman2008>{{cite web|first1=Courtney|last1=Seligman|year=2008|url=http://cseligman.com/text/planets/innerstructure.htm|title=The Structure of the Terrestrial Planets|work=Online Astronomy eText Table of Contents|publisher=cseligman.com|accessdate=2008-02-28}}</ref>
 
<ref name=duennebier1999>{{cite web|last1=Duennebier|first1=Fred|date=1999-08-12|url=http://www.soest.hawaii.edu/GG/ASK/plate-tectonics2.html|title=Pacific Plate Motion|publisher=University of Hawaii|accessdate=2007-03-14}}</ref>
 
<ref name=noaa20070307>{{cite web|display-authors=1|last1=Mueller|first1=R. D.|last2=Roest|first2=W. R.|last3=Royer|first3=J.-Y.|last4=Gahagan|first4=L. M.|last5=Sclater|first5=J. G.|date=2007-03-07|url=http://www.ngdc.noaa.gov/mgg/fliers/96mgg04.html|title=Age of the Ocean Floor Poster|publisher=NOAA|accessdate=2007-03-14}}</ref>
 
<ref name=cmp134_3>{{cite journal|doi=10.1007/s004100050465|title=Priscoan (4.00–4.03 Ga) orthogneisses from northwestern Canada|year=1999|last1=Bowring|first1=Samuel A.|journal=Contributions to Mineralogy and Petrology|volume=134|issue=1|page=3|last2=Williams|first2=Ian S.|bibcode = 1999CoMP..134....3B }}</ref>
 
<ref name=podp2000>{{cite web|last1=Meschede|first1=Martin|last2=Barckhausen|first2=Udo |date=2000-11-20|url=http://www-odp.tamu.edu/publications/170_SR/chap_07/chap_07.htm|title=Plate Tectonic Evolution of the Cocos-Nazca Spreading Center|work=Proceedings of the Ocean Drilling Program|publisher=Texas A&M University|accessdate=2007-04-02}}</ref>
 
<ref name=gps_time_series>{{cite web|author=Staff|url=http://sideshow.jpl.nasa.gov/mbh/series.html|title=GPS Time Series|publisher=NASA JPL|accessdate=2007-04-02}}</ref>
 
<ref name="Pidwirny2006_7">{{cite web|last1=Pidwirny|first1=Michael|year=2006|url=http://www.physicalgeography.net/fundamentals/7h.html|title=Fundamentals of Physical Geography (2nd Edition)|publisher=PhysicalGeography.net|accessdate=2007-03-19}}</ref>
 
<ref name=kring>{{cite web|last1=Kring|first1=David A|url=http://www.lpi.usra.edu/science/kring/epo_web/impact_cratering/intro/|title=Terrestrial Impact Cratering and Its Environmental Effects|publisher=Lunar and Planetary Laboratory|accessdate=2007-03-22}}</ref>
 
<ref name=layers_earth>{{cite web|author=Staff|url=http://volcano.oregonstate.edu/vwdocs/vwlessons/plate_tectonics/part1.html|title=Layers of the Earth|publisher=Volcano World|accessdate=2007-03-11}}</ref>
 
<ref name=jessey>{{cite web|last1=Jessey|first1=David|url=http://geology.csupomona.edu/drjessey/class/Gsc101/Weathering.html|title=Weathering and Sedimentary Rocks|publisher=Cal Poly Pomona|accessdate=2007-03-20}}</ref>
 
<ref name=de_pater_lissauer2010>{{cite book|last1=de Pater|first1=Imke|last2=Lissauer|first2=Jack J.|title=Planetary Sciences|page=154|edition=2nd|publisher=Cambridge University Press|year=2010|isbn=0-521-85371-0}}</ref>
 
<ref name=wekn_bulakh2004>{{cite book|last1=Wenk|first1=Hans-Rudolf|last2=Bulakh|first2=Andreĭ Glebovich|title=Minerals: their constitution and origin|page=359|publisher=Cambridge University Press|year=2004|isbn=0-521-52958-1}}</ref>
 
<ref name=cia>{{cite web|author=Staff|date=2008-07-24|url=https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html|title=World|work=The World Factbook|publisher=Central Intelligence Agency|accessdate=2008-08-05}}</ref>
 
<ref name=fao1994>{{cite book|author=FAO Staff|year=1995|title=FAO Production Yearbook 1994|edition=Volume 48|publisher=Food and Agriculture Organization of the United Nations|location=Rome, Italy|isbn=92-5-003844-5}}</ref>
 
<ref name=sverdrup>{{cite book|first1=H. U.|last1=Sverdrup|last2=Fleming|first2=Richard H.|date=1942-01-01|title=The oceans, their physics, chemistry, and general biology|publisher=Scripps Institution of Oceanography Archives|url=http://repositories.cdlib.org/sio/arch/oceans/|accessdate=2008-06-13|isbn=0-13-630350-1}}</ref>
 
<ref name=kaiko7000>{{cite web|title=7,000&nbsp;m Class Remotely Operated Vehicle ''KAIKO 7000''|url=http://www.jamstec.go.jp/e/about/equipment/ships/kaiko7000.html|publisher=Japan Agency for Marine-Earth Science and Technology (JAMSTEC)|accessdate=2008-06-07}}</ref>
 
<ref name=ocean23_2_112>{{Cite journal|last1=Charette|first1=Matthew A.|last2=Smith|first2=Walter H. F.|title=The Volume of Earth's Ocean|journal=Oceanography|volume=23|issue=2|pages=112–114|date=June 2010|url=http://www.tos.org/oceanography/archive/23-2_charette.pdf|accessdate=2013-06-06|doi=10.5670/oceanog.2010.51}}</ref>
 
<ref name=shiklomanov_et_al_1999>{{cite web|last1=Shiklomanov|first1=Igor A.|year=1999|url=http://webworld.unesco.org/water/ihp/db/shiklomanov/|title=World Water Resources and their use Beginning of the 21st century Prepared in the Framework of IHP UNESCO|publisher=State Hydrological Institute, St. Petersburg|accessdate=2006-08-10}}</ref>
 
<ref name=kennish2001>{{cite book|first1=Michael J.|last1=Kennish|year=2001|title=Practical handbook of marine science|page=35|edition=3rd|publisher=CRC Press|series=Marine science series|isbn=0-8493-2391-6}}</ref>
 
<ref name=mullen2002>{{cite web|last1=Mullen|first1=Leslie|date=2002-06-11|url=http://www.astrobio.net/news/article223.html|title=Salt of the Early Earth|publisher=NASA Astrobiology Magazine|accessdate=2007-03-14}}</ref>
 
<ref name=natsci_oxy4>{{cite web|last1=Morris|first1=Ron M|url=http://replay.waybackmachine.org/20090415082741/http://seis.natsci.csulb.edu/rmorris/oxy/oxy4.html|title=Oceanic Processes|publisher=NASA Astrobiology Magazine|accessdate=2007-03-14}}</ref>
 
<ref name=michon2006>{{cite web|last1=Scott|first1=Michon|date=2006-04-24|url=http://earthobservatory.nasa.gov/Study/HeatBucket/|title=Earth's Big heat Bucket|publisher=NASA Earth Observatory|accessdate=2007-03-14}}</ref>
 
<ref name=sample2005>{{cite web|first1=Sharron|last1=Sample|date=2005-06-21|url=http://science.hq.nasa.gov/oceans/physical/SST.html|title=Sea Surface Temperature|publisher=NASA|accessdate=2007-04-21}}</ref>
 
<ref name=geerts_linacre97>{{cite web|last1=Geerts|first1=B.|last2=Linacre|first2=E.|url=http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html|title=The height of the tropopause|date=November 1997|work=Resources in Atmospheric Sciences|publisher=University of Wyoming|accessdate=2006-08-10}}</ref>
 
<ref name="atmosphere">{{cite web|author=Staff|date=2003-10-08|url=http://www.nasa.gov/audience/forstudents/9-12/features/912_liftoff_atm.html|title=Earth's Atmosphere|publisher=NASA|accessdate=2007-03-21}}</ref>
 
<ref name="moran2005">{{cite web|last1=Moran|first1=Joseph M.|year=2005|url=http://www.nasa.gov/worldbook/weather_worldbook.html|title=Weather|work=World Book Online Reference Center|publisher=NASA/World Book, Inc|accessdate=2007-03-17}}</ref>
 
<ref name="berger2002">{{cite web|last1=Berger|first1=Wolfgang H.|year=2002|url=http://earthguide.ucsd.edu/virtualmuseum/climatechange1/cc1syllabus.shtml|title=The Earth's Climate System|publisher=University of California, San Diego|accessdate=2007-03-24}}</ref>
 
<ref name=rahmstorf2003>{{cite web|first1=Stefan|last1=Rahmstorf|year=2003|url =http://www.pik-potsdam.de/~stefan/thc_fact_sheet.html|title =The Thermohaline Ocean Circulation|publisher=Potsdam Institute for Climate Impact Research|accessdate=2007-04-21}}</ref>
 
<ref name=hydrologic_cycle>{{cite web|author=Various|date=1997-07-21|url=http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/home.rxml|title=The Hydrologic Cycle|publisher=University of Illinois|accessdate=2007-03-24}}</ref>
 
<ref name=sadava_heller2006>{{cite book|last1=Sadava|first1=David E.|last2=Heller|first2=H. Craig|last3=Orians|first3=Gordon H.|title=Life, the Science of Biology|publisher=MacMillan|year=2006|edition=8th|page=1114|isbn=0-7167-7671-5}}</ref>
 
<ref name=climate_zones>{{cite web|author=Staff|url=http://www.ace.mmu.ac.uk/eae/Climate/Older/Climate_Zones.html|title=Climate Zones|publisher=UK Department for Environment, Food and Rural Affairs|accessdate=2007-03-24}}</ref>
 
<ref name=sciweek2004>{{cite web|author=Staff|year=2004|url=http://scienceweek.com/2004/rmps-23.htm|title=Stratosphere and Weather; Discovery of the Stratosphere|publisher=Science Week|accessdate=2007-03-14}}</ref>
 
<ref name=cordoba2004>{{cite web|first1=S. Sanz Fernández|last1=de Córdoba|date=2004-06-21|url=http://www.fai.org/astronautics/100km.asp|title=Presentation of the Karman separation line, used as the boundary separating Aeronautics and Astronautics|publisher=Fédération Aéronautique Internationale|accessdate=2007-04-21}}</ref>
 
<ref name=jas31_4_1118>{{cite journal|last1=Liu|first1=S. C.|last2=Donahue|first2=T. M.|title=The Aeronomy of Hydrogen in the Atmosphere of the Earth|journal=Journal of Atmospheric Sciences|year=1974|volume=31|issue=4|pages=1118–1136|bibcode=1974JAtS...31.1118L|doi=10.1175/1520-0469(1974)031<1118:TAOHIT>2.0.CO;2}}</ref>
 
<ref name=sci293_5531_839>{{cite journal|title=Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth|last1=Catling|first1=David C.|last2=Zahnle|first2=Kevin J.|last3=McKay|first3=Christopher P.|journal=Science|volume=293|issue=5531|pages=839–843|url=http://www.sciencemag.org/cgi/content/full/293/5531/839|doi=10.1126/science.1061976|year=2001|pmid=11486082|bibcode = 2001Sci...293..839C }}</ref>
 
<ref name=abedon1997>{{cite web|last1=Abedon|first1=Stephen T.|date=1997-03-31|url=http://www.mansfield.ohio-state.edu/~sabedon/biol1010.htm|title=History of Earth|publisher=Ohio State University|accessdate=2007-03-19}}</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}}</ref>
 
<ref name=fitzpatrick2006>{{cite web|last1=Fitzpatrick|first1=Richard|date = 2006-02-16|url=http://farside.ph.utexas.edu/teaching/plasma/lectures/node69.html|title=MHD dynamo theory|publisher=NASA WMAP|accessdate=2007-02-27}}</ref>
 
<ref name=campbelwh>{{cite book|last1=Campbell|first1=Wallace Hall|title=Introduction to Geomagnetic Fields|publisher=Cambridge University Press|year=2003|location=New York|page=57|isbn=0-521-82206-8}}</ref>
 
<ref name=stern2005>{{cite web|last1=Stern|first1=David P.|date=2005-07-08|url=http://www-spof.gsfc.nasa.gov/Education/wmap.html|title=Exploration of the Earth's Magnetosphere|publisher=NASA|accessdate=2007-03-21}}</ref>
 
<ref name=USNO_TSD>{{cite web|title=Leap seconds|publisher=Time Service Department, USNO|url=http://tycho.usno.navy.mil/leapsec.html|accessdate=2008-09-23}}</ref>
 
<ref name=IERS>{{cite web|author=Staff|date=2007-08-07|url=http://hpiers.obspm.fr/eop-pc/models/constants.html|title=Useful Constants|publisher=[[International Earth Rotation and Reference Systems Service]]| accessdate=2008-09-23}}</ref>
 
<ref name=seidelmann1992>{{cite book|last1=Seidelmann|first1=P. Kenneth|year=1992|title=Explanatory Supplement to the Astronomical Almanac|page=48|publisher=University Science Books|location=Mill Valley, CA|isbn=0-935702-68-7}}</ref>
 
<ref name=iers1623>{{cite web|author=Staff|url=http://hpiers.obspm.fr/eop-pc/earthor/ut1lod/lod-1623.html|title=IERS Excess of the duration of the day to 86400s&nbsp;... since 1623|publisher=International Earth Rotation and Reference Systems Service (IERS)|accessdate=2008-09-23}}—Graph at end.</ref>
 
<ref name=iers1962>{{cite web|author=Staff|url=http://hpiers.obspm.fr/eop-pc/earthor/ut1lod/figure3.html|archiveurl=https://web.archive.org/web/20070813203913/http://hpiers.obspm.fr/eop-pc/earthor/ut1lod/figure3.html|archivedate=2007-08-13|title=IERS Variations in the duration of the day 1962–2005|publisher=International Earth Rotation and Reference Systems Service (IERS)|accessdate=2008-09-23}}</ref>
 
<ref name=zeilik1998>{{cite book|last1=Zeilik|first1=M.|last2=Gregory|first2=S. A.|title=Introductory Astronomy & Astrophysics|edition=4th|page=56|publisher=Saunders College Publishing|isbn=0-03-006228-4|year=1998}}</ref>
 
<ref name=angular>{{cite web|last1=Williams|first1=David R.|date=2006-02-10|url=http://nssdc.gsfc.nasa.gov/planetary/planetfact.html|title=Planetary Fact Sheets|publisher=NASA|accessdate=2008-09-28}}—See the apparent diameters on the Sun and Moon pages.</ref>
 
<ref name="earth_fact_sheet">{{cite web|last1=Williams|first1=David R.|date=2004-09-01|url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html|title=Earth Fact Sheet|publisher=NASA|accessdate=2010-08-09}}</ref>
 
<ref name="moon_fact_sheet">{{cite web|last1=Williams|first1=David R.|date=2004-09-01|url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html|title=Moon Fact Sheet|publisher=NASA|accessdate=2007-03-21}}</ref>
 
<ref name=vazquez_etal2006>{{cite web|last1=Vázquez|first1=M.|first2=P. Montañés|last2=Rodríguez|last3=Palle|first3=E.|year=2006|url =http://www.iac.es/folleto/research/preprints/files/PP06024.pdf|title=The Earth as an Object of Astrophysical Interest in the Search for Extrasolar Planets|publisher=Instituto de Astrofísica de Canarias|accessdate=2007-03-21 |format=PDF}}</ref>
 
<ref name=nasa20051201>{{cite web|author=Astrophysicist team|date=2005-12-01|url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/030827a.html|title=Earth's location in the Milky Way|publisher=NASA|accessdate=2008-06-11}}</ref>
 
<ref name=bromberg2008>{{cite web|last1=Bromberg|first1=Irv|date=2008-05-01|url=http://www.sym454.org/seasons/|title=The Lengths of the Seasons (on Earth)|publisher=University of Toronto|accessdate=2008-11-08}}</ref>
 
<ref name=lin2006>{{cite web|first1=Haosheng|last1=Lin|title=Animation of precession of moon orbit|work=Survey of Astronomy AST110-6|year=2006|publisher=University of Hawaii at Manoa|url=http://www.ifa.hawaii.edu/users/lin/ast110-6/applets/precession_of_moon_orbit.htm |accessdate=2010-09-10}}</ref>
 
<ref name=williams20051230>{{cite web|last1=Williams|first1=Jack|date=2005-12-20|url=http://www.usatoday.com/weather/tg/wseason/wseason.htm|title=Earth's tilt creates seasons|publisher=USAToday|accessdate=2007-03-17}}</ref>
 
<ref name=fisher19960205>{{cite web|last1=Fisher|first1=Rick|date=1996-02-05|url=http://www.cv.nrao.edu/~rfisher/Ephemerides/earth_rot.html|title=Earth Rotation and Equatorial Coordinates|publisher=National Radio Astronomy Observatory|accessdate=2007-03-21}}</ref>
 
<ref name=espenak_meeus20070207>{{cite web|last1=Espenak|first1=F.|last2=Meeus|first2=J.|date=2007-02-07|url=http://sunearth.gsfc.nasa.gov/eclipse/SEcat5/secular.html|title=Secular acceleration of the Moon|publisher=NASA|accessdate=2007-04-20}}</ref>
 
<ref name=hannu_poropudas19911216>{{cite web|first1=Hannu K. J.|last1=Poropudas|date=1991-12-16|url=http://www.skepticfiles.org/origins/coralclo.htm|title=Using Coral as a Clock|publisher=Skeptic Tank|accessdate = 2007-04-20}}</ref>
 
<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}}</ref>
 
<ref name=nature410_6830_773>{{cite journal|last1=Murray|first1=N.|last2=Holman|first2=M.|title=The role of chaotic resonances in the solar system|journal=Nature|year=2001|volume=410|issue=6830|pages=773–779|arxiv=astro-ph/0111602|doi=10.1038/35071000|pmid=11298438}}</ref>
 
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<ref name=lps27_1437>{{cite journal|last1=Williams|first1=D. M.|first2=J. F.|last2=Kasting|title=Habitable planets with high obliquities|journal=Lunar and Planetary Science|year=1996|volume=27|pages=1437–1438|bibcode=1996LPI....27.1437W|last=Kasting}}</ref> -->
 
<ref name=nature412_708>{{cite journal|last1=Canup|first1=R.|last2=Asphaug|first2=E.|title=Origin of the Moon in a giant impact near the end of the Earth's formation|journal=Nature|volume=412|pages=708–712|year=2001|doi=10.1038/35089010|pmid=11507633|issue=6848|bibcode=2001Natur.412..708C}}</ref>
 
<ref name=whitehouse20021021>{{cite news|first1=David|last1=Whitehouse|title=Earth's little brother found|publisher=BBC News|date=2002-10-21|url=http://news.bbc.co.uk/1/hi/sci/tech/2347663.stm|accessdate=2007-03-31}}</ref>
 
<ref name=ab2003>{{cite web|author=Staff|date=September 2003|url=http://astrobiology.arc.nasa.gov/roadmap/g1.html|title=Astrobiology Roadmap|publisher=NASA, Lockheed Martin|accessdate=2007-03-10}}</ref>
 
<ref name=dole1970>{{cite book|first1=Stephen H.|last1=Dole|year=1970|title=Habitable Planets for Man|edition=2nd|publisher=American Elsevier Publishing Co|url=http://www.rand.org/pubs/reports/R414/|accessdate=2007-03-11|isbn=0-444-00092-5}}</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}}</ref>
 
<ref name=mnpl_utx2006>{{cite web|author=Staff|date=2006-11-24|url=http://www.utexas.edu/tmm/npl/mineralogy/mineral_genesis/|title=Mineral Genesis: How do minerals form?|publisher=Non-vertebrate Paleontology Laboratory, Texas Memorial Museum|accessdate=2007-04-01}}</ref>
 
<ref name=science299_5607_673>{{cite journal|last1=Rona|first1=Peter A.|title=Resources of the Sea Floor|journal=Science|year=2003|volume=299|issue=5607|pages=673–674|url=http://www.sciencemag.org/cgi/content/full/299/5607/673?ijkey=AHVbRrqUsmdHY&keytype=ref&siteid=sci|accessdate=2007-02-04|doi = 10.1126/science.1080679|pmid = 12560541}}</ref>
 
<ref name=un20070202>{{cite web|author=Staff|date = 2007-02-02|url=http://www.un.org/apps/news/story.asp?NewsID=21429&Cr=climate&Cr1=change|title=Evidence is now 'unequivocal' that humans are causing global warming&nbsp;– UN report|publisher=United Nations|accessdate=2007-03-07|archiveurl=http://replay.waybackmachine.org/20081221031717/http://www.un.org/apps/news/story.asp?NewsID=21429&Cr=climate&Cr1=change|archivedate=21 December 2008}}</ref>
 
<ref name="World_Population_Clock">{{cite web |author=[[United States Census Bureau]] |url=http://www.census.gov/population/popclockworld.html |title=World POP Clock Projection |work=United States Census Bureau International Database |date=2 November 2011 |accessdate= 2011-11-02 }}</ref>
 
<ref name=un2006>{{cite web|author=Staff|url=http://www.un.org/esa/population/publications/wpp2006/wpp2006.htm|archiveurl=http://replay.waybackmachine.org/20090905200753/http://www.un.org/esa/population/publications/wpp2006/wpp2006.htm|archivedate=5 September 2009|title=World Population Prospects: The 2006 Revision|publisher=United Nations|accessdate=2007-03-07}}</ref>
 
<ref name=prb2007>{{cite web|author=Staff|year=2007|url=http://www.prb.org/Educators/TeachersGuides/HumanPopulation/PopulationGrowth/QuestionAnswer.aspx|title=Human Population: Fundamentals of Growth: Growth|publisher=Population Reference Bureau|accessdate=2007-03-31}}</ref>
 
<ref name=hessd4_439>{{cite journal|last1=Peel|first1=M. C.|last2=Finlayson|first2=B. L.|last3=McMahon|first3=T. A.|title=Updated world map of the Köppen-Geiger climate classification|journal=Hydrology and Earth System Sciences Discussions|year=2007|volume=4|issue=2|pages=439–473|url=http://www.hydrol-earth-syst-sci-discuss.net/4/439/2007/hessd-4-439-2007.html|accessdate=2007-03-31|doi=10.5194/hessd-4-439-2007}}</ref>
 
<ref name=biodiv>{{cite web|author=Staff|url=http://www.biodiv.org/programmes/default.shtml|title=Themes & Issues|publisher=Secretariat of the Convention on Biological Diversity|accessdate=2007-03-29}}</ref>
 
<ref name=cfsa2006>{{cite web|author=Staff|date=2006-08-15|url=http://www.tscm.com/alert.html|title=Canadian Forces Station (CFS) Alert|publisher=Information Management Group|accessdate=2007-03-31}}</ref>
 
<ref name=kennedy1989>{{cite book|first1=Paul|last1=Kennedy|authorlink1=Paul Kennedy|year=1989|title=[[The Rise and Fall of the Great Powers]]|edition=1st|publisher=Vintage|isbn=0-679-72019-7}}</ref>
 
<ref name=uncharter>{{cite web|url=http://www.un.org/aboutun/charter/|title=U.N. Charter Index|publisher=United Nations|accessdate=2008-12-23|archiveurl=http://replay.waybackmachine.org/20090220011242/http://www.un.org/aboutun/charter/|archivedate=20 February 2009}}</ref>
 
<ref name=un_int_law>{{cite web|author=Staff|url=http://www.un.org/law/|title=International Law|publisher=United Nations|accessdate=2007-03-27|archiveurl=http://replay.waybackmachine.org/20081231055149/http://www.un.org/law/|archivedate=31 December 2009}}</ref>
 
<ref name=kuhn2006>{{cite book|first1=Betsy|last1=Kuhn|year=2006|title=The race for space: the United States and the Soviet Union compete for the new frontier|page=34|publisher=Twenty-First Century Books|isbn=0-8225-5984-6}}</ref>
 
<ref name=ellis2004>{{cite book|first1=Lee|last1=Ellis|year=2004|title=Who's who of NASA Astronauts|publisher=Americana Group Publishing|isbn=0-9667961-4-4}}</ref>
 
<ref name=shayler_vis2005>{{cite book|first1=David|last1=Shayler|first2=Bert|last2=Vis|year=2005|title=Russia's Cosmonauts: Inside the Yuri Gagarin Training Center|publisher=Birkhäuser|isbn=0-387-21894-7}}</ref>
 
<ref name=wade2008>{{cite web|last1=Wade|first1=Mark|date=2008-06-30|url=http://www.astronautix.com/articles/aststics.htm|accessdate=2008-12-23|title=Astronaut Statistics|publisher=Encyclopedia Astronautica}}</ref>
 
<ref name=nasa_rg_iss2007>{{cite web|date=2007-01-16|url=http://www.nasa.gov/mission_pages/station/news/ISS_Reference_Guide.html|title=Reference Guide to the International Space Station|publisher=NASA|accessdate=2008-12-23}}</ref>
 
<ref name=cramb2007>{{cite news|first1=Auslan|last1=Cramb|publisher=Telegraph|title=Nasa's Discovery extends space station|date=2007-10-28|url=http://www.telegraph.co.uk/earth/earthnews/3311903/Nasas-Discovery-extends-space-station.html|accessdate=2009-03-23}}</ref>
 
<ref name=liungman2004>{{cite book|first1=Carl G.|last1=Liungman|year=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=91-972705-0-4}}</ref>
 
<ref name=arnett20060716>{{cite web|first1=Bill|last1=Arnett|date=July 16, 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|accessdate=2010-03-09}}</ref>
 
<ref name=Dutch2002>{{cite journal|last1=Dutch|first1=S. I.|year=2002|title=Religion as belief versus religion as fact|journal=Journal of Geoscience Education|volume=50|issue=2|pages=137–144|url=http://nagt.org/files/nagt/jge/abstracts/Dutch_v50n2p137.pdf|accessdate=2008-04-28|format=PDF}}</ref>
 
<ref name=edis2003>{{cite book|first1=Taner|last1=Edis|year=2003|title=A World Designed by God: Science and Creationism in Contemporary Islam|publisher=Amherst: Prometheus|url=http://www2.truman.edu/~edis/writings/articles/CFI-2001.pdf|isbn=1-59102-064-6|accessdate=2008-04-28|format=PDF}}</ref>
 
<ref name=jge53_3_319>{{cite journal|last1=Ross|first1=M. R.|year=2005|title=Who Believes What? Clearing up Confusion over Intelligent Design and Young-Earth Creationism|journal=Journal of Geoscience Education|volume=53|issue=3|page=319|url=http://www.nagt.org/files/nagt/jge/abstracts/Ross_v53n3p319.pdf|accessdate=2008-04-28|format=PDF}}</ref>
 
<ref name=arghg4_143>{{cite journal|last1=Pennock|first1=R. T.|title=Creationism and intelligent design|journal=Annual Review of Genomics Human Genetics|volume=4|issue=1|pages=143–63|year=2003|pmid=14527300|doi=10.1146/annurev.genom.4.070802.110400}}</ref>
 
<ref name=sec_nap2008>{{cite book|author=National Academy of Sciences, Institute of Medicine|title=Science, Evolution, and Creationism|url=http://books.nap.edu/openbook.php?record_id=11876&page=R1|year=2008|publisher=National Academies Press|location=Washington, D.C|isbn=0-309-10586-2|accessdate=2011-03-13}}</ref>
 
<ref name=jrst43_4_419>{{cite journal|last1=Colburn,|first1=A.|last2=Henriques|first2=Laura|year=2006|title=Clergy views on evolution, creationism, science, and religion|journal=Journal of Research in Science Teaching|volume=43|issue=4|pages=419–442|doi=10.1002/tea.20109|bibcode = 2006JRScT..43..419C }}</ref>
 
<ref name=frye1983>{{cite book|last1=Frye|first1=Roland Mushat|year = 1983|title=Is God a Creationist? The Religious Case Against Creation-Science|publisher=Scribner's|isbn=0-684-17993-8}}</ref>
 
<ref name=nathist106_2_16>{{cite journal|last1=Gould|first1=S. J.|year=1997|title=Nonoverlapping magisteria|journal=Natural History|volume=106|issue=2|pages=16–22|url=http://www.jbburnett.com/resources/gould_nonoverlapping.pdf|accessdate=2008-04-28|format=PDF}}</ref>
 
<ref name=russell1997>{{cite web|last1=Russell|first1=Jeffrey B|url=http://www.asa3.org/ASA/topics/history/1997Russell.html|title=The Myth of the Flat Earth|publisher=American Scientific Affiliation|accessdate=2007-03-14}}; but see also [[Cosmas Indicopleustes]].</ref>
 
<ref name=jacobs19980201>{{cite web|last1=Jacobs|first1=James Q.|date=1998-02-01|url=http://www.jqjacobs.net/astro/aegeo.html|title=Archaeogeodesy, a Key to Prehistory|accessdate=2007-04-21}}</ref>
<!--UNUSED
<ref name=fuller1963>{{cite book|first1=R. Buckminster|last1=Fuller|authorlink=Buckminster Fuller|year=1963|title=Operating Manual for Spaceship Earth|edition=First|publisher=E.P. Dutton & Co|location=New York|isbn=0-525-47433-1|url=http://www.futurehi.net/docs/OperatingManual.html|accessdate=2007-04-21}}</ref>
 
<ref name=lovelock1979>{{cite book|first1=James E.|last1=Lovelock|authorlink1=James Lovelock|year=1979|title=Gaia: A New Look at Life on Earth|edition=First|publisher=Oxford University Press|location=Oxford|isbn=0-19-286030-5}}</ref>
 
<ref name=mcmichael1993>For example: {{cite book|first1=Anthony J.|last1=McMichael|year=1993|title=Planetary Overload: Global Environmental Change and the Health of the Human Species|publisher=Cambridge University Press|isbn=0-521-45759-9}}</ref>-->
 
<ref name=aj136_5_1906>{{cite journal|last1=McCarthy|first1=Dennis D.|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}}</ref>
 
<ref name=jg31_3_267>{{cite journal|last1=Pollack|first1=Henry N.|last2=Hurter|first2=Suzanne J.|last3=Johnson|first3=Jeffrey R.|title=Heat flow from the Earth's interior: Analysis of the global data set|journal=Reviews of Geophysics|volume=31|issue=3|pages=267–280|date=August 1993|doi=10.1029/93RG01249|bibcode=1993RvGeo..31..267P |url=http://www.agu.org/journals/ABS/1993/93RG01249.shtml}}</ref>
 
<ref name=lang2003>{{cite book|first1=Kenneth R.|last1=Lang|year=2003|title=The Cambridge guide to the solar system|page=92|publisher=Cambridge University Press|isbn=0-521-81306-9}}</ref>
 
<ref name=usno>{{cite web|title=Selected Astronomical Constants, 2011|work=The Astronomical Almanac|url=http://asa.usno.navy.mil/SecK/2011/Astronomical_Constants_2011.txt|accessdate=2011-02-25}}</ref>
 
<ref name=christou_asher2011>{{cite arXiv | last1=Christou|first1=Apostolos A.|last2=Asher|first2=David J. | date=March 31, 2011 | title=A long-lived horseshoe companion to the Earth | eprint=1104.0036 | class=astro-ph.EP}} See table 2, p. 5.</ref>
 
<ref name=ucs>{{cite web | title=UCS Satellite Database | date=January 31, 2011 | work=Nuclear Weapons & Global Security | publisher=Union of Concerned Scientists | url=http://www.ucsusa.org/nuclear_weapons_and_global_security/space_weapons/technical_issues/ucs-satellite-database.html | accessdate=2011-05-12 }}</ref>
 
<ref name=Connors>{{cite journal |last1=Connors |first1=Martin |last2=Wiegert |first2=Paul |last3=Veillet |first3=Christian |title=Earth's Trojan asteroid |date=July 27, 2011 |journal=[[Nature (journal)|Nature]] |volume=475 |pages=481–483 |url=http://www.nature.com/nature/journal/v475/n7357/full/nature10233.html |doi=10.1038/nature10233 |accessdate=2011-07-27 |issue=7357|bibcode = 2011Natur.475..481C |pmid=21796207}}</ref>
 
<ref name=Choi>{{cite web |last1=Choi |first1=Charles Q. |title=First Asteroid Companion of Earth Discovered at Last |url=http://www.space.com/12443-earth-asteroid-companion-discovered-2010-tk7.html |date=July 27, 2011 |publisher=[[Space.com]] |accessdate=2011-07-27 }}</ref>
 
<ref name=walsh2008>{{cite book | first1=Patrick J. | last=Walsh | title=Oceans and human health: risks and remedies from the seas | page=212 | editors=Sharon L. Smith, Lora E. Fleming | publisher=Academic Press, 2008 | isbn=0-12-372584-4 | url=http://books.google.com/books?id=c6J5hlcjFaAC&pg=PA212 | date=1997-05-16 }}</ref>
 
<ref name="Turner1990">{{cite book
| first1    = B. L., II
| last1    = Turner
| title    = The Earth As Transformed by Human Action: Global And Regional Changes in the Biosphere Over the Past 300 Years
| publisher = CUP Archive
| page      = 164
| year      = 1990
| isbn      = 0521363578
| url      = http://books.google.com/books?id=7GI0AAAAIAAJ&pg=PA164
| postscript= .
}}</ref>
 
<ref name="Lambina2011">{{Cite journal
| first1    = Eric F.
| last1    = Lambina
| first2    = Patrick
| last2    = Meyfroidt
| title    = Global land use change, economic globalization, and the looming land scarcity
| work      = Proceedings of the National Academy of Sciences of the United States of America
| publisher = National Academy of Sciences
| pages    = 3465–3472
| volume    = 108
| issue    = 9
| date      = March 1, 2011
| url      = http://www.pnas.org/content/108/9/3465.full.pdf
| accessdate= 2013-04-2013
|bibcode = 2011PNAS..108.3465L |doi = 10.1073/pnas.1100480108 }} See Table 1.</ref>
}}
 
<!-- Unused citation
<ref name=sec1014>{{cite journal|last1=Guillemot|first1=H.|last2=Greffoz|first2=V.|title=Ce que sera la fin du monde|journal=Science et Vie|date=March 2002|volume=N° 1014|language=French}}</ref>
<ref name=randhouse2005>{{cite book|month=July|year=2005|title=Random House Unabridged Dictionary|publisher=Random House|isbn=0-375-42599-3}}</ref>
-->
 
==Further reading==
* {{cite book
|first=Neil F. |last=Comins
|year=2001
|title=Discovering the Essential Universe
|edition=2nd
|publisher=W. H. Freeman
|bibcode=2003deu..book.....C
|isbn=0-7167-5804-0}}
 
==External links==
{{sisterlinks|Earth}}
* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Earth Earth&nbsp;– Profile]&nbsp;– [http://solarsystem.nasa.gov/ Solar System Exploration]&nbsp;– [[NASA]].
* [http://www.ncdc.noaa.gov/oa/climate/globalextremes.html Earth&nbsp;– Temperature and Precipitation Extremes]&nbsp;– [[National Climatic Data Center|NCDC]].
* [http://www.nasa.gov/centers/goddard/earthandsun/earthshape.html Earth&nbsp;– Climate Changes Cause Shape to Change]&nbsp;– [[NASA]].
* [http://geomag.usgs.gov/ Earth&nbsp;– Geomagnetism Program]&nbsp;– [[USGS]].
* [http://eol.jsc.nasa.gov/Coll/weekly.htm Earth&nbsp;– Astronaut Photography Gateway]&nbsp;– [[NASA]].
* [http://earthobservatory.nasa.gov/ Earth&nbsp;– Observatory]&nbsp;– [[NASA]].
* [http://www.astronomycast.com/stars/episode-51-earth/ Earth&nbsp;– Audio (29:28)&nbsp;– Cain/Gay&nbsp;– Astronomy Cast (2007)].
* Earth&nbsp;– Videos&nbsp;– [[International Space Station]]:
** [https://www.youtube.com/watch?v=74mhQyuyELQ Video (01:02)]&nbsp;– Earth (Time-Lapse).
** [https://www.youtube.com/watch?v=l6ahFFFQBZY Video (00:27)]&nbsp;– Earth and [[Aurora (astronomy)|Auroras]] (Time-Lapse).
{{Spoken Wikipedia-4|2012-06-13|EARTH_-_WIKIPEDIA_SPOKEN_ARTICLE_(Part_01).ogg|EARTH_-_WIKIPEDIA_SPOKEN_ARTICLE_(Part_02).ogg|EARTH_-_WIKIPEDIA_SPOKEN_ARTICLE_(Part_03).ogg|EARTH_-_WIKIPEDIA_SPOKEN_ARTICLE_(Part_04).ogg}}
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Latest revision as of 01:36, 13 January 2015



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