Earth

Earth
	The Blue Marble, Apollo 17, December 1972
Designations
Alternative names	The world, the globe, Sol III, Terra, Tellus, Gaia, Mother Earth
Adjectives	Earthly, terrestrial, terran, tellurian
Symbol	and
Orbital characteristics
	Epoch J2000<ref group="n" name="epoch" />
Aphelion	152097597 km (94509065 mi)
Perihelion	147098450 km (91402740 mi)<ref group="n" name="apsis" />
Semi-major axis	149598023 km (92955902 mi)<ref name="VSOP87" />
Eccentricity	0.0167086<ref name="VSOP87" />
Orbital period (sidereal)	365.256363004 dj)1.00001742096 a*
Average orbital speed	29.7827 km/s)107218 km/h; 66622 mph*
Mean anomaly	358.617°
Inclination	7.155° – Sun's equator;; 0.00005° – J2000 ecliptic;
Longitude of ascending node	−11.26064° – J2000 ecliptic<ref name="earth_fact_sheet" />
Time of perihelion	2023-Jan-04<ref>Park, Ryan (9 May 2022). "Horizons Batch Call for 2023 Perihelion". NASA/JPL. Retrieved 3 July 2022.</ref>
Argument of perihelion	114.20783°<ref name="earth_fact_sheet" />
Satellites	1, the Moon
Physical characteristics
Mean radius	6371.0 km (3958.8 mi)<ref name="hbcp2000" />
Equatorial radius	6378.137 km (3963.191 mi)<ref name=usno /><ref name="WGS-84" />
Polar radius	6356.752 km (3949.903 mi)<ref name="cazenave_ahrens1995" />
Flattening	1/298.257222101 (ETRS89)<ref name="IERS2004" />
Surface area	Land: 148940000 km2; (57510000 sq mi); Water: 361132000 km2; (139434000 sq mi);
Volume	1.08321×1012 km3 (2.59876×1011 cu mi)<ref name="earth_fact_sheet" />
Mass	5.972168×1024 kg (1.31668×1025 lb)<ref name="earthmass" />
Mean density	5.5134 g/cm3; (0.19918 lb/cu in)<ref name="earth_fact_sheet" />
Surface gravity	9.80665 m/s2; (32.1740 ft/s2)<ref name="NIST2008" />
Moment of inertia factor	0.3307<ref name="Williams1994" />
Escape velocity	11.186 km/s (40270 km/h; 25020 mph)<ref name="earth_fact_sheet" />
Synodic rotation period	1.0 d ; (24h 00 m 00s)
Sidereal rotation period	display: inline-block; line-height: 1.2em; padding: .1em 0; width: 100%;
Equatorial rotation velocity	0.4651 km/s)1674.4 km/h; 1040.4 mph*
Axial tilt	23.4392811°<ref name="IERS" />
Temperature	255 K (−18 °C; −1 °F); (blackbody temperature)<ref name="American Chemical Society 2013">"Atmospheres and Planetary Temperatures". American Chemical Society. 18 July 2013. Archived from the original on 27 January 2023. Retrieved 3 January 2023.</ref>
Surface equivalent dose rate	0.274 μSv/h<ref>United Nations Scientific Committee on the Effects of Atomic Radiation (2008). Sources and effects of ionizing radiation. New York: United Nations (published 2010). Table 1. ISBN 978-92-1-142274-0. Retrieved 9 November 2012.</ref>
Absolute magnitude (H)	−3.99
Atmosphere
Surface pressure	101.325 kPa (at sea level)
Composition by volume	78.08% nitrogen (dry air); 20.95% oxygen (dry air); ≤1% water vapor (variable); 0.9340% argon; 0.0415% carbon dioxide; 0.00182% neon; 0.00052% helium; 0.00017% methane; 0.00011% krypton; 0.00006% hydrogen; Source:<ref name="earth_fact_sheet" />

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

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

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

Earth, like most other bodies in the Solar System, formed 4.5 billion years ago from gas in the early Solar System. During the first billion years of Earth's history, the ocean formed and then life developed within it. Life spread globally and has been altering Earth's atmosphere and surface, leading to the Great Oxidation Event two billion years ago. Humans emerged 300,000 years ago in Africa and have spread across every continent on Earth. Humans depend on Earth's biosphere and natural resources for their survival, but have increasingly impacted the planet's environment. Humanity's current impact on Earth's climate and biosphere is unsustainable, threatening the livelihood of humans and many other forms of life, and causing widespread extinctions.<ref>"What Is Climate Change?". United Nations. Retrieved 17 August 2022.</ref>

Etymology

The Modern English word Earth developed, via Middle English, from an Old English noun most often spelled eorðe.<ref name="oedearth">"earth, n.¹". Oxford English Dictionary (3 ed.). Oxford, England: Oxford University Press. 2010. doi:10.1093/acref/9780199571123.001.0001. ISBN 978-0-19-957112-3.</ref> It has cognates in every Germanic language, and their ancestral root has been reconstructed as *erþō. In its earliest attestation, the word eorðe was used to translate the many senses of Latin terra and Greek γῆ gē: the ground, its soil, dry land, the human world, the surface of the world (including the sea), and the globe itself. As with Roman Terra/Tellūs and Greek Gaia, Earth may have been a personified goddess in Germanic paganism: late Norse mythology included Jörð ("Earth"), a giantess often given as the mother of Thor.<ref>Simek, Rudolf (2007). Dictionary of Northern Mythology. Translated by Hall, Angela. D.S. Brewer. p. 179. ISBN 978-0-85991-513-7.</ref>

Historically, "Earth" has been written in lowercase. Beginning with the use of Early Middle English, its definite sense as "the globe" was expressed as "the earth". By the era of Early Modern English, capitalization of nouns began to prevail, and the earth was also written the Earth, particularly when referenced along with other heavenly bodies. More recently, the name is sometimes simply given as Earth, by analogy with the names of the other planets, though "earth" and forms with "the earth" remain common.<ref name="oedearth" /> House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name, such as a description of the "Earth's atmosphere", but employs the lowercase when it is preceded by "the", such as "the atmosphere of the earth"). It almost always appears in lowercase in colloquial expressions such as "what on earth are you doing?"<ref>"earth". The New Oxford Dictionary of English (1st ed.). Oxford: Oxford University Press. 1998. ISBN 978-0-19-861263-6.</ref>

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

There are a number of adjectives for the planet Earth. The word "earthly" is derived from "Earth". From the Latin Terra comes terran /ˈtɛrən/,<ref>"Terran". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)</ref> terrestrial /təˈrɛstriəl/,<ref>"terrestrial". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)</ref> and (via French) terrene /təˈriːn/,<ref>"terrene". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)</ref> and from the Latin Tellus comes tellurian /tɛˈlʊəriən/<ref>"tellurian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)</ref> and telluric.<ref>"telluric". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 31 March 2021.</ref>

Natural history

Formation

The oldest material found in the Solar System is dated to 4.5682+0.0002
−0.0004 Ga (billion years) ago.<ref name=bouvier_wadhwa2010 /> By 4.54±0.04 Ga the primordial Earth had formed.<ref name="age_earth1" /> The bodies in the Solar System formed and evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, and dust (including primordial nuclides). According to nebular theory, planetesimals formed by accretion, with the primordial Earth being estimated as likely taking anywhere from 70 to 100 million years to form.<ref>Righter, K.; Schonbachler, M. (7 May 2018). "Ag Isotopic Evolution of the Mantle During Accretion: New Constraints from Pd and Ag Metal–Silicate Partitioning". Differentiation: Building the Internal Architecture of Planets. 2084: 4034. Bibcode:2018LPICo2084.4034R. Retrieved 25 October 2020.</ref>

Estimates of the age of the Moon range from 4.5 Ga to significantly younger.<ref>Tartèse, Romain; Anand, Mahesh; Gattacceca, Jérôme; Joy, Katherine H.; Mortimer, James I.; Pernet-Fisher, John F.; Russell, Sara; Snape, Joshua F.; Weiss, Benjamin P. (2019). "Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples". Space Science Reviews. 215 (8): 54. Bibcode:2019SSRv..215...54T. doi:10.1007/s11214-019-0622-x. ISSN 1572-9672.</ref> A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object with about 10% of Earth's mass, named Theia, collided with Earth.<ref name=reilly20091022 /> It hit Earth with a glancing blow and some of its mass merged with Earth.<ref name="canup_asphaug2001b" /><ref>Meier, M. M. M.; Reufer, A.; Wieler, R. (4 August 2014). "On the origin and composition of Theia: Constraints from new models of the Giant Impact". Icarus. 242: 5. arXiv:1410.3819. Bibcode:2014Icar..242..316M. doi:10.1016/j.icarus.2014.08.003. S2CID 119226112.</ref> Between approximately 4.1 and 3.8 Ga, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth.<ref>Claeys, Philippe; Morbidelli, Alessandro (2011). "Late Heavy Bombardment". In Gargaud, Muriel; Amils, Prof Ricardo; Quintanilla, José Cernicharo; Cleaves II, Henderson James (Jim); Irvine, William M.; Pinti, Prof Daniele L.; Viso, Michel (eds.). Encyclopedia of Astrobiology. Springer Berlin Heidelberg. pp. 909–912. doi:10.1007/978-3-642-11274-4_869. ISBN 978-3-642-11271-3.</ref>

After formation

Earth's atmosphere and oceans were formed by volcanic activity and outgassing.<ref>"Earth's Early Atmosphere and Oceans". Lunar and Planetary Institute. Universities Space Research Association. Retrieved 27 June 2019.</ref> Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids, protoplanets, and comets.<ref name="watersource" /> Sufficient water to fill the oceans may have been on Earth since it formed.<ref>Piani, Laurette; et al. (2020). "Earth's water may have been inherited from material similar to enstatite chondrite meteorites". Science. 369 (6507): 1110–1113. Bibcode:2020Sci...369.1110P. doi:10.1126/science.aba1948. ISSN 0036-8075. PMID 32855337. S2CID 221342529.</ref> In this model, atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity.<ref name="asp2002" /> By 3.5 Ga, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.<ref name="physorg20100304" />

*Pale orange dot*, an artist's impression of Early Earth, featuring its tinted orange methane-rich early atmosphere<ref name="Trainer Pavlov DeWitt Jimenez pp. 18035–18042">Trainer, Melissa G.; et al. (28 November 2006). "Organic haze on Titan and the early Earth". *Proceedings of the National Academy of Sciences*. **103** (48): 18035–18042. doi:10.1073/pnas.0608561103. ISSN 0027-8424. PMC 1838702. PMID 17101962.</ref>

As the molten outer layer of Earth cooled it formed the first solid crust, which is thought to have been mafic in composition. The first continental crust, which was more felsic in composition, formed by the partial melting of this mafic crust.<ref name="comp">McDonough, W.F.; Sun, S.-s. (1995). "The composition of the Earth". Chemical Geology. 120 (3–4): 223–253. Bibcode:1995ChGeo.120..223M. doi:10.1016/0009-2541(94)00140-4.</ref> The presence of grains of the mineral zircon of Hadean age in Eoarchean sedimentary rocks suggests that at least some felsic crust existed as early as 4.4 Ga, only 140 Ma after Earth's formation.<ref name="science310_5756_1947" /> There are two main models of how this initial small volume of continental crust evolved to reach its current abundance:<ref name="williams_santosh2004" /> (1) a relatively steady growth up to the present day,<ref name="science164_1229" /> which is supported by the radiometric dating of continental crust globally and (2) an initial rapid growth in the volume of continental crust during the Archean, forming the bulk of the continental crust that now exists,<ref name="ajes38_613" /><ref name="tp322_19" /> which is supported by isotopic evidence from hafnium in zircons and neodymium in sedimentary rocks. The two models and the data that support them can be reconciled by large-scale recycling of the continental crust, particularly during the early stages of Earth's history.<ref name="Dhuime_etal_2018" />

New continental crust forms as a result of plate tectonics, a process ultimately driven by the continuous loss of heat from Earth's interior. Over the period of hundreds of millions of years, tectonic forces have caused areas of continental crust to group together to form supercontinents that have subsequently broken apart. At approximately 750 Ma, one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia at 600–540 Ma, then finally Pangaea, which also began to break apart at 180 Ma.<ref name="bradley_2011" />

The most recent pattern of ice ages began about 40 Ma,<ref>Kinzler, Ro. "When and how did the ice age end? Could another one start?". Ology. American Museum of Natural History. Retrieved 27 June 2019.</ref> and then intensified during the Pleistocene about 3 Ma.<ref>Chalk, Thomas B.; et al. (12 December 2007). "Causes of ice age intensification across the Mid-Pleistocene Transition". Proc Natl Acad Sci U S A. 114 (50): 13114–13119. doi:10.1073/pnas.1702143114. PMC 5740680. PMID 29180424.</ref> High- and middle-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating about every 21,000, 41,000 and 100,000 years.<ref name="psc" /> The Last Glacial Period, colloquially called the "last ice age", covered large parts of the continents, to the middle latitudes, in ice and ended about 11,700 years ago.<ref>Turner, Chris S.M.; et al. (2010). "The potential of New Zealand kauri (Agathis australis) for testing the synchronicity of abrupt climate change during the Last Glacial Interval (60,000–11,700 years ago)". Quaternary Science Reviews. Elsevier. 29 (27–28): 3677–3682. Bibcode:2010QSRv...29.3677T. doi:10.1016/j.quascirev.2010.08.017. Retrieved 3 November 2020.</ref>

Origin of life and evolution

Chemical reactions led to the first self-replicating molecules about four billion years ago. A half billion years later, the last common ancestor of all current life arose.<ref name="sa282_6_90" /> The evolution of photosynthesis allowed the Sun's energy to be harvested directly by life forms. The resultant molecular oxygen (O₂) accumulated in the atmosphere and due to interaction with ultraviolet solar radiation, formed a protective ozone layer (O₃) in the upper atmosphere.<ref name="NYT-20131003">Zimmer, Carl (3 October 2013). "Earth's Oxygen: A Mystery Easy to Take for Granted". The New York Times. Archived from the original on 3 October 2013. Retrieved 3 October 2013.</ref> The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes.<ref name="jas22_3_225" /> True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized Earth's surface.<ref name="burton20021129" /> Among the earliest fossil evidence for life is microbial mat fossils found in 3.48 billion-year-old sandstone in Western Australia,<ref>Noffke, Nora; Christian, Daniel; Wacey, David; Hazen, Robert M. (8 November 2013). "Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia". Astrobiology. 13 (12): 1103–1124. Bibcode:2013AsBio..13.1103N. doi:10.1089/ast.2013.1030. PMC 3870916. PMID 24205812.</ref> biogenic graphite found in 3.7 billion-year-old metasedimentary rocks in Western Greenland,<ref>Ohtomo, Yoko; Kakegawa, Takeshi; Ishida, Akizumi; et al. (January 2014). "Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks". Nature Geoscience. 7 (1): 25–28. Bibcode:2014NatGe...7...25O. doi:10.1038/ngeo2025. ISSN 1752-0894. S2CID 54767854.</ref> and remains of biotic material found in 4.1 billion-year-old rocks in Western Australia.<ref>Borenstein, Seth (19 October 2015). "Hints of life on what was thought to be desolate early Earth". Excite. Yonkers, NY: Mindspark Interactive Network. Associated Press. Archived from the original on 18 August 2016. Retrieved 20 October 2015.</ref><ref>Bell, Elizabeth A.; Boehnike, Patrick; Harrison, T. Mark; Mao, Wendy L. (19 October 2015). "Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon". Proc. Natl. Acad. Sci. U.S.A. 112 (47): 14518–4521. Bibcode:2015PNAS..11214518B. doi:10.1073/pnas.1517557112. ISSN 1091-6490. PMC 4664351. PMID 26483481. Early edition, published online before print.</ref> The earliest direct evidence of life on Earth is contained in 3.45 billion-year-old Australian rocks showing fossils of microorganisms.<ref>Tyrell, Kelly April (18 December 2017). "Oldest fossils ever found show life on Earth began before 3.5 billion years ago". University of Wisconsin–Madison. Retrieved 18 December 2017.</ref><ref>Schopf, J. William; Kitajima, Kouki; Spicuzza, Michael J.; Kudryavtsev, Anatolly B.; Valley, John W. (2017). "SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions". PNAS. 115 (1): 53–58. Bibcode:2018PNAS..115...53S. doi:10.1073/pnas.1718063115. PMC 5776830. PMID 29255053.</ref>

An artist's impression of the Archean, the eon after Earth's formation, featuring round stromatolites, which are early oxygen-producing forms of life from billions of years ago. After the Late Heavy Bombardment, Earth's crust had cooled, its water-rich barren surface is marked by continents and volcanoes, with the Moon still orbiting Earth half as far as it is today, appearing 2.8 times larger and producing strong tides.<ref name="Lunar and Planetary Institute">"Earth-Moon Dynamics". *Lunar and Planetary Institute*. Retrieved 2 September 2022.</ref>

During the Neoproterozoic, 1000 to 539 Ma, much of Earth might have been covered in ice. This hypothesis has been termed "Snowball Earth", and it is of particular interest because it preceded the Cambrian explosion, when multicellular life forms significantly increased in complexity.<ref>Brooke, John L. (2014). Climate Change and the Course of Global History. Cambridge University Press. p. 42. ISBN 978-0-521-87164-8.</ref><ref>Cabej, Nelson R. (2019). Epigenetic Mechanisms of the Cambrian Explosion. Elsevier Science. p. 56. ISBN 978-0-12-814312-4.</ref> Following the Cambrian explosion, 535 Ma, there have been at least five major mass extinctions and many minor ones.<ref name="Stanley_2016" /> Apart from the proposed current Holocene extinction event, the most recent was 66 Ma, when an asteroid impact triggered the extinction of the non-avian dinosaurs and other large reptiles, but largely spared small animals such as insects, mammals, lizards and birds. Mammalian life has diversified over the past 66 Mys, and several million years ago an African ape species gained the ability to stand upright.<ref name="gould1994" />^{[better source needed]} This facilitated tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which led to the evolution of humans. The development of agriculture, and then civilization, led to humans having an influence on Earth and the nature and quantity of other life forms that continues to this day.<ref name="bgsa119_1_140" />

Future

Earth's expected long-term future is tied to that of the Sun. Over the next 1.1 billion years, solar luminosity will increase by 10%, and over the next 3.5 billion years by 40%.<ref name="sun_future" /> Earth's increasing surface temperature will accelerate the inorganic carbon cycle, reducing CO₂ concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in approximately 100–900 million years.<ref name="britt2000" /><ref name="pnas1_24_9576" /> The lack of vegetation will result in the loss of oxygen in the atmosphere, making animal life impossible.<ref name="ward_brownlee2002" /> Due to the increased luminosity, Earth's mean temperature may reach 100 °C (212 °F) in 1.5 billion years, and all ocean water will evaporate and be lost to space, which may trigger a runaway greenhouse effect, within an estimated 1.6 to 3 billion years.<ref name="Mello-2020">Mello, Fernando de Sousa; Friaça, Amâncio César Santos (2020). "The end of life on Earth is not the end of the world: converging to an estimate of life span of the biosphere?". International Journal of Astrobiology. 19 (1): 25–42. Bibcode:2020IJAsB..19...25D. doi:10.1017/S1473550419000120. ISSN 1473-5504.</ref> Even if the Sun were stable, a fraction of the water in the modern oceans will descend to the mantle, due to reduced steam venting from mid-ocean ridges.<ref name="Mello-2020" /><ref name="hess5_4_569" />

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

Physical characteristics

Size and shape

Earth has a rounded shape, through hydrostatic equilibrium,<ref name="Horner 2021">Horner, Jonti (16 July 2021). "I've always wondered: why are the stars, planets and moons round, when comets and asteroids aren't?". The Conversation. Retrieved 3 March 2023.</ref> with an average diameter of 12,742 kilometers (7,918 mi), making it the fifth largest planetary sized and largest terrestrial object of the Solar System.<ref>Lea, Robert (6 July 2021). "How big is Earth?". Space.com. Archived from the original on 9 January 2024. Retrieved 11 January 2024.</ref>

Due to Earth's rotation it has the shape of an ellipsoid, bulging at its Equator; its diameter is 43 kilometers (27 mi) longer there than at its poles.<ref name="ngdc2006" /><ref name="milbert_smith96" /> Earth's shape furthermore has local topographic variations. Though the largest local variations, like the Mariana Trench (10,925 meters or 35,843 feet below local sea level),<ref>Stewart, Heather A.; Jamieson, Alan J. (2019). "The five deeps: The location and depth of the deepest place in each of the world's oceans". Earth-Science Reviews. 197: 102896. Bibcode:2019ESRv..19702896S. doi:10.1016/j.earscirev.2019.102896. ISSN 0012-8252.</ref> only shortens Earth's average radius by 0.17% and Mount Everest (8,848 meters or 29,029 feet above local sea level) lengthens it by only 0.14%.<ref group="n"> If Earth were shrunk to the size of a billiard ball, some areas of Earth such as large mountain ranges and oceanic trenches would feel like tiny imperfections, whereas much of the planet, including the Great Plains and the abyssal plains, would feel smoother.<ref>"Is a Pool Ball Smoother than the Earth?" (PDF). Billiards Digest. 1 June 2013. Retrieved 26 November 2014.</ref></ref><ref>Tewksbury, Barbara. "Back-of-the-Envelope Calculations: Scale of the Himalayas". Carleton University. Retrieved 19 October 2020.</ref> Since Earth's surface is farthest out from Earth's center of mass at its equatorial bulge, the summit of the volcano Chimborazo in Ecuador (6,384.4 km or 3,967.1 mi) is its farthest point out.<ref name=ps20_5_16 /><ref>Krulwich, Robert (7 April 2007). "The 'Highest' Spot on Earth". NPR. Retrieved 31 July 2012.</ref> Parallel to the rigid land topography the Ocean exhibits a more dynamic topography.<ref>"Ocean Surface Topography". Ocean Surface Topography from Space. NASA. Retrieved 16 June 2022.</ref>

To measure the local variation of Earth's topography, geodesy employs an idealized Earth producing a shape called a geoid. Such a geoid shape is gained if the ocean is idealized, covering Earth completely and without any perturbations such as tides and winds. The result is a smooth but gravitational irregular geoid surface, providing a mean sea level (MSL) as a reference level for topographic measurements.<ref>"What is the geoid?". National Ocean Service. Retrieved 10 October 2020.</ref>

Surface

Earth's surface is the boundary between the atmosphere, and the solid Earth and oceans. Defined in this way, it has an area of about 510 million km² (197 million sq mi).<ref name="Pidwirny 2006_8" /> Earth can be divided into two hemispheres: by latitude into the polar Northern and Southern hemispheres; or by longitude into the continental Eastern and Western hemispheres.

Most of Earth's surface is ocean water: 70.8% or 361 million km² (139 million sq mi).<ref name="Percentage">"8(o) Introduction to the Oceans". www.physicalgeography.net.</ref> This vast pool of salty water is often called the world ocean,<ref name="Janin Mandia 2012 p. 20">Janin, H.; Mandia, S.A. (2012). Rising Sea Levels: An Introduction to Cause and Impact. McFarland, Incorporated, Publishers. p. 20. ISBN 978-0-7864-5956-8. Retrieved 26 August 2022.</ref><ref name="Ro 2020">Ro, Christine (3 February 2020). "Is It Ocean Or Oceans?". Forbes. Retrieved 26 August 2022.</ref> and makes Earth with its dynamic hydrosphere a water world<ref name="Smith 2021">Smith, Yvette (7 June 2021). "Earth Is a Water World". NASA. Retrieved 27 August 2022.</ref><ref name="National Geographic Society 2022">"Water-Worlds". National Geographic Society. 20 May 2022. Retrieved 24 August 2022.</ref> or ocean world.<ref name="Lunine 2017 pp. 123–130">Lunine, Jonathan I. (2017). "Ocean worlds exploration". Acta Astronautica. Elsevier BV. 131: 123–130. Bibcode:2017AcAau.131..123L. doi:10.1016/j.actaastro.2016.11.017. ISSN 0094-5765.</ref><ref name="Ocean Worlds">"Ocean Worlds". Ocean Worlds. Archived from the original on 27 August 2022. Retrieved 27 August 2022.</ref> Indeed, in Earth's early history the ocean may have covered Earth completely.<ref name="Voosen p.">Voosen, Paul (9 March 2021). "Ancient Earth was a water world". Science. American Association for the Advancement of Science (AAAS). 371 (6534): 1088–1089. doi:10.1126/science.abh4289. ISSN 0036-8075. PMID 33707245. S2CID 241687784.</ref> The world ocean is commonly divided into the Pacific Ocean, Atlantic Ocean, Indian Ocean, Antarctic or Southern Ocean, and Arctic Ocean, from largest to smallest. The ocean covers Earth's oceanic crust, but to a lesser extent with shelf seas also shelves of the continental crust. The oceanic crust forms large oceanic basins with features like abyssal plains, seamounts, submarine volcanoes,<ref name="ngdc2006" /> oceanic trenches, submarine canyons, oceanic plateaus, and a globe-spanning mid-ocean ridge system.

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

Earth's land covers 29.2%, or 149 million km² (58 million sq mi) of Earth's surface. The land surface includes many islands around the globe, but most of the land surface is taken by the four continental landmasses, which are (in descending order): Africa-Eurasia, America (landmass), Antarctica, and Australia (landmass).<ref name="DunnMitchell2016">Dunn, Ross E.; Mitchell, Laura J.; Ward, Kerry (2016). The New World History: A Field Guide for Teachers and Researchers. Univ of California Press. pp. 232–. ISBN 978-0-520-28989-5.</ref><ref name="Dempsey 2013">Dempsey, Caitlin (15 October 2013). "Geography Facts about the World's Continents". Geography Realm. Retrieved 26 August 2022.</ref><ref name="McColl">R.W. McColl, ed. (2005). "continents". Encyclopedia of World Geography. Vol. 1. Facts on File, Inc. p. 215. ISBN 978-0-8160-7229-3. Retrieved 25 August 2022. And since Africa and Asia are connected at the Suez Peninsula, Europe, Africa, and Asia are sometimes combined as Afro-Eurasia or Eurafrasia. The International Olympic Committee's official flag, containing [...] the single continent of America (North and South America being connected as the Isthmus of Panama).</ref> These landmasses are further broken down and grouped into the continents. The terrain of the land surface varies greatly and consists of mountains, deserts, plains, plateaus, and other landforms. The elevation of the land surface varies from a low point of −418 m (−1,371 ft) at the Dead Sea, to a maximum altitude of 8,848 m (29,029 ft) at the top of Mount Everest. The mean height of land above sea level is about 797 m (2,615 ft).<ref>Center, National Geophysical Data (19 August 2020). "Hypsographic Curve of Earth's Surface from ETOPO1". ngdc.noaa.gov.</ref>

Land can be covered by surface water, snow, ice, artificial structures or vegetation. Most of Earth's land hosts vegetation,<ref name="Carlowicz Simmon 2019">Carlowicz, Michael; Simmon, Robert (15 July 2019). "Seeing Forests for the Trees and the Carbon: Mapping the World's Forests in Three Dimensions". NASA Earth Observatory. Retrieved 31 December 2022.</ref> but ice sheets (10%,<ref name="National Geographic Society 2006">"Ice Sheet". National Geographic Society. 6 August 2006. Retrieved 3 January 2023.</ref> not including the equally large land under permafrost)<ref name="Obu 2021 p.">Obu, J. (2021). "How Much of the Earth's Surface is Underlain by Permafrost?". Journal of Geophysical Research: Earth Surface. American Geophysical Union (AGU). 126 (5). Bibcode:2021JGRF..12606123O. doi:10.1029/2021jf006123. ISSN 2169-9003. S2CID 235532921.</ref> or cold as well as hot deserts (33%)<ref name="Cain 2010">Cain, Fraser (1 June 2010). "What Percentage of the Earth's Land Surface is Desert?". Universe Today. Retrieved 3 January 2023.</ref> occupy also considerable amounts of it.

The pedosphere is the outermost layer of Earth's land surface and is composed of soil and subject to soil formation processes. Soil is crucial for land to be arable. Earth's total arable land is 10.7% of the land surface, with 1.3% being permanent cropland.<ref>"World Bank arable land". World Bank. Retrieved 19 October 2015.</ref><ref>"World Bank permanent cropland". World Bank. Retrieved 19 October 2015.</ref> Earth has an estimated 16.7 million km² (6.4 million sq mi) of cropland and 33.5 million km² (12.9 million sq mi) of pastureland.<ref name="Hooke2012">Hooke, Roger LeB.; Martín-Duque, José F.; Pedraza, Javier (December 2012). "Land transformation by humans: A review" (PDF). GSA Today. 22 (12): 4–10. Bibcode:2012GSAT...12l...4H. doi:10.1130/GSAT151A.1.</ref>

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

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

Earth's surface is continually being shaped by internal plate tectonic processes including earthquakes and volcanism; by weathering and erosion driven by ice, water, wind and temperature; and by biological processes including the growth and decomposition of biomass into soil.<ref name="kring" /><ref>Martin, Ronald (2011). Earth's Evolving Systems: The History of Planet Earth. Jones & Bartlett Learning. ISBN 978-0-7637-8001-2. OCLC 635476788.</ref>

Tectonic plates

Earth's mechanically rigid outer layer of Earth's crust and upper mantle, the lithosphere, is divided into tectonic plates. These plates are rigid segments that move relative to each other at one of three boundaries types: at convergent boundaries, two plates come together; at divergent boundaries, two plates are pulled apart; and at transform boundaries, two plates slide past one another laterally. Along these plate boundaries, earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur.<ref name="kious_tilling1999" /> The tectonic plates ride on top of the asthenosphere, the solid but less-viscous part of the upper mantle that can flow and move along with the plates.<ref name="seligman2008" />

As the tectonic plates migrate, oceanic crust is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes recycles the oceanic crust back into the mantle. Due to this recycling, most of the ocean floor is less than 100 Ma old. The oldest oceanic crust is located in the Western Pacific and is estimated to be 200 Ma old.<ref name=duennebier1999 /><ref name=noaa20070307 /> By comparison, the oldest dated continental crust is 4,030 Ma,<ref name=cmp134_3 /> although zircons have been found preserved as clasts within Eoarchean sedimentary rocks that give ages up to 4,400 Ma, indicating that at least some continental crust existed at that time.<ref name=science310_5756_1947 />

The seven major plates are the Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, and South American. Other notable plates include the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. The Australian Plate fused with the Indian Plate between 50 and 55 Ma. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/a (3.0 in/year)<ref name=podp2000 /> and the Pacific Plate moving 52–69 mm/a (2.0–2.7 in/year). At the other extreme, the slowest-moving plate is the South American Plate, progressing at a typical rate of 10.6 mm/a (0.42 in/year).<ref name="Argus_etal_2011">Argus, D.F.; Gordon, R.G.; DeMets, C. (2011). "Geologically current motion of 56 plates relative to the no-net-rotation reference frame". Geochemistry, Geophysics, Geosystems. 12 (11): n/a. Bibcode:2011GGG....1211001A. doi:10.1029/2011GC003751.</ref>

Internal structure

Geologic layers of Earth<ref name=pnas76_9_4192>Jordan, T. H. (1979). "Structural geology of the Earth's interior". *Proceedings of the National Academy of Sciences of the United States of America*. 76 (9): 4192–4200. Bibcode:1979PNAS...76.4192J. doi:10.1073/pnas.76.9.4192. PMC 411539. PMID 16592703.</ref>
Depth<ref name=robertson2001>Robertson, Eugene C. (26 July 2001). "The Interior of the Earth". USGS. Retrieved 24 March 2007.</ref> (km)	Component layer name	Density (g/cm³)
Illustration of Earth's cutaway, not to scale
0–60	Lithosphere<ref group="n">Locally varies between 5 and 200 km.</ref>	—
0–35	Crust<ref group="n">Locally varies between 5 and 70 km.</ref>	2.2–2.9
35–660	Upper mantle	3.4–4.4
660–2890	Lower mantle	3.4–5.6
100–700	Asthenosphere	—
2890–5100	Outer core	9.9–12.2
5100–6378	Inner core	12.8–13.1

Earth's interior, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties. The outer layer is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity.<ref name="GeolSoc" /> The thickness of the crust varies from about 6 kilometers (3.7 mi) under the oceans to 30–50 km (19–31 mi) for the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, which is divided into independently moving tectonic plates.<ref>Micalizio, Caryl-Sue; Evers, Jeannie (20 May 2015). "Lithosphere". National Geographic. Retrieved 13 October 2020.</ref>

Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 km (250 and 410 mi) below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core.<ref name=tanimoto_ahrens1995 /> Earth's inner core may be rotating at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year, although both somewhat higher and much lower rates have also been proposed.<ref name="Deuss_2014" /> The radius of the inner core is about one-fifth of that of Earth. Density increases with depth, as described in the table on the right.

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

Chemical composition

Earth's mass is approximately 5.97×10²⁴ kg (5,970 Yg). It is composed mostly of iron (32.1% by mass), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminum (1.4%), with the remaining 1.2% consisting of trace amounts of other elements. Due to gravitational separation, the core is primarily composed of the denser elements: iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.<ref name="pnas71_12_6973" /><ref name="comp" /> The most common rock constituents of the crust are oxides. Over 99% of the crust is composed of various oxides of eleven elements, principally oxides containing silicon (the silicate minerals), aluminum, iron, calcium, magnesium, potassium, or sodium.<ref name="brown_mussett1981" /><ref name="pnas71_12_6973" />

Internal heat

The major heat-producing isotopes within Earth are potassium-40, uranium-238, and thorium-232.<ref name=sanders20031210 /> At the center, the temperature may be up to 6,000 °C (10,830 °F),<ref>"The Earth's Centre is 1000 Degrees Hotter than Previously Thought". The European Synchrotron (ESRF). 25 April 2013. Archived from the original on 28 June 2013. Retrieved 12 April 2015.</ref> and the pressure could reach 360 GPa (52 million psi).<ref name=ptrsl360_1795_1227 /> Because much of the heat is provided by radioactive decay, scientists postulate that early in Earth's history, before isotopes with short half-lives were depleted, Earth's heat production was much higher. At approximately 3 Gyr, twice the present-day heat would have been produced, increasing the rates of mantle convection and plate tectonics, and allowing the production of uncommon igneous rocks such as komatiites that are rarely formed today.<ref name="T&S 137" /><ref name=epsl121_1 />

The mean heat loss from Earth is 87 mW m⁻², for a global heat loss of 4.42×10¹³ W.<ref name=jg31_3_267 /> A portion of the core's thermal energy is transported toward the crust by mantle plumes, a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts.<ref name=science246_4926_103 /> More of the heat in Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs under the oceans because the crust there is much thinner than that of the continents.<ref name="heat loss" />

Gravitational field

The gravity of Earth is the acceleration that is imparted to objects due to the distribution of mass within Earth. Near Earth's surface, gravitational acceleration is approximately 9.8 m/s² (32 ft/s²). Local differences in topography, geology, and deeper tectonic structure cause local and broad regional differences in Earth's gravitational field, known as gravity anomalies.<ref>Watts, A. B.; Daly, S. F. (May 1981). "Long wavelength gravity and topography anomalies". Annual Review of Earth and Planetary Sciences. 9 (1): 415–418. Bibcode:1981AREPS...9..415W. doi:10.1146/annurev.ea.09.050181.002215.</ref>

Magnetic field

The main part of Earth's magnetic field is generated in the core, the site of a dynamo process that converts the kinetic energy of thermally and compositionally driven convection into electrical and magnetic field energy. The field extends outwards from the core, through the mantle, and up to Earth's surface, where it is, approximately, a dipole. The poles of the dipole are located close to Earth's geographic poles. At the equator of the magnetic field, the magnetic-field strength at the surface is 3.05×10⁻⁵ T, with a magnetic dipole moment of 7.79×10²² Am² at epoch 2000, decreasing nearly 6% per century (although it still remains stronger than its long time average).<ref name="dipole">Olson, Peter; Amit, Hagay (2006). "Changes in earth's dipole" (PDF). Naturwissenschaften. 93 (11): 519–542. Bibcode:2006NW.....93..519O. doi:10.1007/s00114-006-0138-6. PMID 16915369. S2CID 22283432.</ref> The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes secular variation of the main field and field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.<ref name="fitzpatrick2006" /><ref name="campbelwh" />

The extent of Earth's magnetic field in space defines the magnetosphere. Ions and electrons of the solar wind are deflected by the magnetosphere; solar wind pressure compresses the dayside of the magnetosphere, to about 10 Earth radii, and extends the nightside magnetosphere into a long tail.<ref>Ganushkina, N. Yu; Liemohn, M. W.; Dubyagin, S. (2018). "Current Systems in the Earth's Magnetosphere". Reviews of Geophysics. 56 (2): 309–332. Bibcode:2018RvGeo..56..309G. doi:10.1002/2017RG000590. hdl:2027.42/145256. ISSN 1944-9208. S2CID 134666611. Archived from the original on 31 March 2021. Retrieved 24 October 2020.</ref> Because the velocity of the solar wind is greater than the speed at which waves propagate through the solar wind, a supersonic bow shock precedes the dayside magnetosphere within the solar wind.<ref>Masson, Arnaud (11 May 2007). "Cluster reveals the reformation of the Earth's bow shock". European Space Agency. Retrieved 16 August 2016.</ref> Charged particles are contained within the magnetosphere; the plasmasphere is defined by low-energy particles that essentially follow magnetic field lines as Earth rotates.<ref>Gallagher, Dennis L. (14 August 2015). "The Earth's Plasmasphere". NASA/Marshall Space Flight Center. Retrieved 16 August 2016.</ref><ref>Gallagher, Dennis L. (27 May 2015). "How the Plasmasphere is Formed". NASA/Marshall Space Flight Center. Archived from the original on 15 November 2016. Retrieved 16 August 2016.</ref> The ring current is defined by medium-energy particles that drift relative to the geomagnetic field, but with paths that are still dominated by the magnetic field,<ref name="BaumjohannTreumann1997">Baumjohann, Wolfgang; Treumann, Rudolf A. (1997). Basic Space Plasma Physics. World Scientific. pp. 8, 31. ISBN 978-1-86094-079-8.</ref> and the Van Allen radiation belts are formed by high-energy particles whose motion is essentially random, but contained in the magnetosphere.<ref name="Britannica">McElroy, Michael B. (2012). "Ionosphere and magnetosphere". Encyclopædia Britannica. Encyclopædia Britannica, Inc.</ref><ref name="Van Allen">Van Allen, James Alfred (2004). Origins of Magnetospheric Physics. University of Iowa Press. ISBN 978-0-87745-921-7. OCLC 646887856.</ref>

During magnetic storms and substorms, charged particles can be deflected from the outer magnetosphere and especially the magnetotail, directed along field lines into Earth's ionosphere, where atmospheric atoms can be excited and ionized, causing the aurora.<ref name="stern2005" />

Orbit and rotation

Rotation

Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time (86,400.0025 SI seconds).<ref name="aj136_5_1906" /> Because Earth's solar day is now slightly longer than it was during the 19th century due to tidal deceleration, each day varies between 0 and 2 ms longer than the mean solar day.<ref name="USNO_TSD" /><ref>"Rapid Service/Prediction of Earth Orientation". IERS Bulletin-A. 28 (15). 9 April 2015. Archived from the original (.DAT file (displays as plaintext in browser)) on 14 March 2015. Retrieved 12 April 2015.</ref>

Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86,164.0989 seconds of mean solar time (UT1), or 23^h 56^m 4.0989^s.<ref name="IERS" /><ref group="n" name="Aoki" /> Earth's rotation period relative to the precessing or moving mean March equinox (when the Sun is at 90° on the equator), is 86,164.0905 seconds of mean solar time (UT1) (23^h 56^m 4.0905^s).<ref name="IERS" /> Thus the sidereal day is shorter than the stellar day by about 8.4 ms.<ref name="seidelmann1992" />

Apart from meteors within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in Earth's sky is to the west at a rate of 15°/h = 15'/min. For bodies near the celestial equator, this is equivalent to an apparent diameter of the Sun or the Moon every two minutes; from Earth's surface, the apparent sizes of the Sun and the Moon are approximately the same.<ref name="zeilik1998" /><ref name="angular" />

Orbit

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

Earth orbits the Sun every 365.2564 mean solar days, or one sidereal year. With an apparent movement of the Sun in Earth's sky at a rate of about 1°/day eastward, which is one apparent Sun or Moon diameter every 12 hours. Due to this motion, on average it takes 24 hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the meridian.

The orbital speed of Earth averages about 29.78 km/s (107,200 km/h; 66,600 mph), which is fast enough to travel a distance equal to Earth's diameter, about 12,742 km (7,918 mi), in seven minutes, and the distance to the Moon, 384,000 km (239,000 mi), in about 3.5 hours.<ref name="earth_fact_sheet" />

The Moon and Earth orbit a common barycenter every 27.32 days relative to the background stars. When combined with the Earth–Moon system's common orbit around the Sun, the period of the synodic month, from new moon to new moon, is 29.53 days. Viewed from the celestial north pole, the motion of Earth, the Moon, and their axial rotations are all counterclockwise. Viewed from a vantage point above the Sun and Earth's north poles, Earth orbits in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.44 degrees from the perpendicular to the Earth–Sun plane (the ecliptic), and the Earth-Moon plane is tilted up to ±5.1 degrees against the Earth–Sun plane. Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses.<ref name="earth_fact_sheet" /><ref name="moon_fact_sheet" />

The Hill sphere, or the sphere of gravitational influence, of Earth is about 1.5 million km (930,000 mi) in radius.<ref name="vazquez_etal2006" /><ref group="n" name="hill_radius" /> This is the maximum distance at which Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.<ref name="vazquez_etal2006" /> Earth, along with the Solar System, is situated in the Milky Way and orbits about 28,000 light-years from its center. It is about 20 light-years above the galactic plane in the Orion Arm.<ref name="nasa20051201" />

Axial tilt and seasons

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

During the summer, the day lasts longer, and the Sun climbs higher in the sky. In winter, the climate becomes cooler and the days shorter.<ref>Rohli, Robert. V.; Vega, Anthony J. (2018). Climatology (fourth ed.). Jones & Bartlett Learning. pp. 291–292. ISBN 978-1-284-12656-3.</ref> Above the Arctic Circle and below the Antarctic Circle there is no daylight at all for part of the year, causing a polar night, and this night extends for several months at the poles themselves. These same latitudes also experience a midnight sun, where the sun remains visible all day.<ref>Burn, Chris (March 1996). The Polar Night (PDF). The Aurora Research Institute. Retrieved 28 September 2015.</ref><ref>"Sunlight Hours". Australian Antarctic Programme. 24 June 2020. Retrieved 13 October 2020.</ref>

By astronomical convention, the four seasons can be determined by the solstices—the points in the orbit of maximum axial tilt toward or away from the Sun—and the equinoxes, when Earth's rotational axis is aligned with its orbital axis. In the Northern Hemisphere, winter solstice currently occurs around 21 December; summer solstice is near 21 June, spring equinox is around 20 March and autumnal equinox is about 22 or 23 September. In the Southern Hemisphere, the situation is reversed, with the summer and winter solstices exchanged and the spring and autumnal equinox dates swapped.<ref name="bromberg2008" />

The angle of Earth's axial tilt is relatively stable over long periods of time. Its axial tilt does undergo nutation; a slight, irregular motion with a main period of 18.6 years.<ref name="lin2006" /> The orientation (rather than the angle) of Earth's axis also changes over time, precessing around in a complete circle over each 25,800-year cycle; this precession is the reason for the difference between a sidereal year and a tropical year. Both of these motions are caused by the varying attraction of the Sun and the Moon on Earth's equatorial bulge. The poles also migrate a few meters across Earth's surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. Earth's rotational velocity also varies in a phenomenon known as length-of-day variation.<ref name="fisher19960205" />

In modern times, Earth's perihelion occurs around 3 January, and its aphelion around 4 July. These dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. The changing Earth–Sun distance causes an increase of about 6.8% in solar energy reaching Earth at perihelion relative to aphelion.<ref>Buis, Alan (27 February 2020). "Milankovitch (Orbital) Cycles and Their Role in Earth's Climate". NASA. Retrieved 27 October 2020.</ref><ref group="n" name="solar_energy" /> Because the Southern Hemisphere is tilted toward the Sun at about the same time that Earth reaches the closest approach to the Sun, the Southern Hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. This effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of water in the Southern Hemisphere.<ref>Kang, Sarah M.; Seager, Richard. "Croll Revisited: Why is the Northern Hemisphere Warmer than the Southern Hemisphere?" (PDF). Columbia University. New York. Retrieved 27 October 2020.</ref>

Earth–Moon system

Moon

The Moon is a relatively large, terrestrial, planet-like natural satellite, with a diameter about one-quarter of Earth's. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger relative to the dwarf planet Pluto.<ref>Klemetti, Erik (17 June 2019). "What's so special about our Moon, anyway?". Astronomy. Retrieved 13 October 2020.</ref><ref>"Charon". NASA. 19 December 2019. Retrieved 13 October 2020.</ref> The natural satellites of other planets are also referred to as "moons", after Earth's.<ref>Brown, Toby (2 December 2019). "Curious Kids: Why is the moon called the moon?". The Conversation. Retrieved 13 October 2020.</ref> The most widely accepted theory of the Moon's origin, the giant-impact hypothesis, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. This hypothesis explains the Moon's relative lack of iron and volatile elements and the fact that its composition is nearly identical to that of Earth's crust.<ref name="canup_asphaug2001b" />

The gravitational attraction between Earth and the Moon causes tides on Earth.<ref>Coughenour, Christopher L.; Archer, Allen W.; Lacovara, Kenneth J. (2009). "Tides, tidalites, and secular changes in the Earth–Moon system". Earth-Science Reviews. 97 (1): 59–79. Bibcode:2009ESRv...97...59C. doi:10.1016/j.earscirev.2009.09.002. ISSN 0012-8252.</ref> The same effect on the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit Earth. As a result, it always presents the same face to the planet.<ref>Kelley, Peter (17 August 2017). "Tidally locked exoplanets may be more common than previously thought". Uw News. Retrieved 8 October 2020.</ref> As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases.<ref>"Lunar Phases and Eclipses | Earth's Moon". NASA Solar System Exploration. Retrieved 8 October 2020.</ref> Due to their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm/a (1.5 in/year). Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23 µs/yr—add up to significant changes.<ref name="espenak_meeus20070207" /> During the Ediacaran period, for example, (approximately 620 Ma) there were 400±7 days in a year, with each day lasting 21.9±0.4 hours.<ref>Williams, G.E. (2000). "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". Reviews of Geophysics. 38 (1): 37–59. Bibcode:2000RvGeo..38...37W. doi:10.1029/1999RG900016. S2CID 51948507.</ref>

The Moon may have dramatically affected the development of life by moderating the planet's climate. Paleontological evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon.<ref name="aaa428_261" /> Some theorists think that without this stabilization against the torques applied by the Sun and planets to Earth's equatorial bulge, the rotational axis might be chaotically unstable, exhibiting large changes over millions of years, as is the case for Mars, though this is disputed.<ref>Cooper, Keith (27 January 2015). "Earth's moon may not be critical to life". Phys.org. Retrieved 26 October 2020.</ref><ref>Dadarich, Amy; Mitrovica, Jerry X.; Matsuyama, Isamu; Perron, J. Taylor; Manga, Michael; Richards, Mark A. (22 November 2007). "Equilibrium rotational stability and figure of Mars" (PDF). Icarus. 194 (2): 463–475. doi:10.1016/j.icarus.2007.10.017. Archived from the original (PDF) on 1 December 2020. Retrieved 26 October 2020.</ref>

Viewed from Earth, the Moon is just far enough away to have almost the same apparent-sized disk as the Sun. The angular size (or solid angle) of these two bodies match because, although the Sun's diameter is about 400 times as large as the Moon's, it is also 400 times more distant.<ref name="angular" /> This allows total and annular solar eclipses to occur on Earth.<ref>Sharf, Caleb A. (18 May 2012). "The Solar Eclipse Coincidence". Scientific American. Retrieved 13 October 2020.</ref>

On 1 November 2023, scientists reported that, according to computer simulations, remnants of a protoplanet, named Theia, could be inside the Earth, left over from a collision with the Earth in ancient times, and afterwards becoming the Moon.<ref name="NYT-20231101">Chang, Kenneth (1 November 2023). "A 'Big Whack' Formed the Moon and Left Traces Deep in Earth, a Study Suggests - Two enormous blobs deep inside Earth could be remnants of the birth of the moon". The New York Times. Archived from the original on 1 November 2023. Retrieved 2 November 2023.</ref><ref name="NAT-20231101">Yuan, Qian; et al. (1 November 2023). "Moon-forming impactor as a source of Earth's basal mantle anomalies". Nature. 623 (7985): 95–99. Bibcode:2023Natur.623...95Y. doi:10.1038/s41586-023-06589-1. PMID 37914947. S2CID 264869152. Archived from the original on 2 November 2023. Retrieved 2 November 2023.</ref>

Asteroids and artificial satellites

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

Earth's co-orbital asteroids population consists of quasi-satellites, objects with a horseshoe orbit and trojans. There are at least five quasi-satellites, including 469219 Kamoʻoalewa.<ref name="christou_asher2011" /><ref>Marcos, C. de la Fuente; Marcos, R. de la Fuente (8 August 2016). "Asteroid (469219) 2016 HO3, the smallest and closest Earth quasi-satellite". Monthly Notices of the Royal Astronomical Society. 462 (4): 3441–3456. arXiv:1608.01518. Bibcode:2016MNRAS.462.3441D. doi:10.1093/mnras/stw1972. S2CID 118580771. Retrieved 28 October 2020.</ref> A trojan asteroid companion, 2010 TK7, is librating around the leading Lagrange triangular point, L4, in Earth's orbit around the Sun.<ref name="Choi" /> The tiny near-Earth asteroid 2006 RH120 makes close approaches to the Earth–Moon system roughly every twenty years. During these approaches, it can orbit Earth for brief periods of time.<ref>"2006 RH120 ( = 6R10DB9) (A second moon for the Earth?)". Great Shefford Observatory. Archived from the original on 6 February 2015. Retrieved 17 July 2015.</ref>

As of September 2021^[update], there are 4,550 operational, human-made satellites orbiting Earth.<ref name="ucs" /> There are also inoperative satellites, including Vanguard 1, the oldest satellite currently in orbit, and over 16,000 pieces of tracked space debris.<ref group="n" name="space_debris" /> Earth's largest artificial satellite is the International Space Station.<ref>Welch, Rosanne; Lamphier, Peg A. (2019). Technical Innovation in American History: An Encyclopedia of Science and Technology [3 volumes]. ABC-CLIO. p. 126. ISBN 978-1-61069-094-2.</ref>

Hydrosphere

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

The mass of the oceans is approximately 1.35×10¹⁸ metric tons or about 1/4400 of Earth's total mass. The oceans cover an area of 361.8 million km² (139.7 million sq mi) with a mean depth of 3,682 m (12,080 ft), resulting in an estimated volume of 1.332 billion km³ (320 million cu mi).<ref name="ocean23_2_112" /> If all of Earth's crustal surface were at the same elevation as a smooth sphere, the depth of the resulting world ocean would be 2.7 to 2.8 km (1.68 to 1.74 mi).<ref>"Third rock from the Sun – restless Earth". NASA's Cosmos. Retrieved 12 April 2015.</ref> About 97.5% of the water is saline; the remaining 2.5% is fresh water.<ref>European Investment Bank (2019). On Water. Publications Office. doi:10.2867/509830. ISBN 9789286143199. Retrieved 7 December 2020.</ref><ref>Khokhar, Tariq (22 March 2017). "Chart: Globally, 70% of Freshwater is Used for Agriculture". World Bank Blogs. Retrieved 7 December 2020.</ref> Most fresh water, about 68.7%, is present as ice in ice caps and glaciers.<ref>Perlman, Howard (17 March 2014). "The World's Water". USGS Water-Science School. Retrieved 12 April 2015.</ref> The remaining 30% is ground water, 1% surface water (covering only 2.8% of Earth's land)<ref name="Lake Scientist 2016">"Where Are Lakes?". Lake Scientist. 28 February 2016. Retrieved 28 February 2023.</ref> and other small forms of fresh water deposits such as permafrost, water vapor in the atmosphere, biological binding, etc. .<ref name="School 2019">School, Water Science (13 November 2019). "How Much Water is There on Earth? – U.S. Geological Survey". USGS.gov. Retrieved 3 March 2023.</ref><ref name="Education 2022">"Freshwater Resources". Education. 18 August 2022. Retrieved 28 February 2023.</ref>

In Earth's coldest regions, snow survives over the summer and changes into ice. This accumulated snow and ice eventually forms into glaciers, bodies of ice that flow under the influence of their own gravity. Alpine glaciers form in mountainous areas, whereas vast ice sheets form over land in polar regions. The flow of glaciers erodes the surface changing it dramatically, with the formation of U-shaped valleys and other landforms.<ref>Hendrix, Mark (2019). Earth Science: An Introduction. Boston: Cengage. p. 330. ISBN 978-0-357-11656-2.</ref> Sea ice in the Arctic covers an area about as big as the United States, although it is quickly retreating as a consequence of climate change.<ref>Hendrix, Mark (2019). Earth Science: An Introduction. Boston: Cengage. p. 329. ISBN 978-0-357-11656-2.</ref>

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

The abundance of water, particularly liquid water, on Earth's surface is a unique feature that distinguishes it from other planets in the Solar System. Solar System planets with considerable atmospheres do partly host atmospheric water vapor, but they lack surface conditions for stable surface water.<ref name="Center 2021">Center, Astrogeology Science (14 October 2021). "Tour of Water in the Solar System – U.S. Geological Survey". USGS.gov. Retrieved 19 January 2022.</ref> Despite some moons showing signs of large reservoirs of extraterrestrial liquid water, with possibly even more volume than Earth's ocean, all of them are large bodies of water under a kilometers thick frozen surface layer.<ref>"Are there oceans on other planets?". NOAA's National Ocean Service. 1 June 2013. Retrieved 19 January 2022.</ref>

Atmosphere

The atmospheric pressure at Earth's sea level averages 101.325 kPa (14.696 psi),<ref name="Exline2006">Exline, Joseph D.; Levine, Arlene S.; Levine, Joel S. (2006). Meteorology: An Educator's Resource for Inquiry-Based Learning for Grades 5–9 (PDF). NASA/Langley Research Center. p. 6. NP-2006-08-97-LaRC.</ref> with a scale height of about 8.5 km (5.3 mi).<ref name="earth_fact_sheet" /> A dry atmosphere is composed of 78.084% nitrogen, 20.946% oxygen, 0.934% argon, and trace amounts of carbon dioxide and other gaseous molecules.<ref name="Exline2006" /> Water vapor content varies between 0.01% and 4%<ref name="Exline2006" /> but averages about 1%.<ref name="earth_fact_sheet" /> Clouds cover around two-thirds of Earth's surface, more so over oceans than land.<ref name="King Platnick Menzel Ackerman 2013 pp. 3826–3852">King, Michael D.; Platnick, Steven; Menzel, W. Paul; Ackerman, Steven A.; Hubanks, Paul A. (2013). "Spatial and Temporal Distribution of Clouds Observed by MODIS Onboard the Terra and Aqua Satellites". IEEE Transactions on Geoscience and Remote Sensing. Institute of Electrical and Electronics Engineers (IEEE). 51 (7): 3826–3852. Bibcode:2013ITGRS..51.3826K. doi:10.1109/tgrs.2012.2227333. hdl:2060/20120010368. ISSN 0196-2892. S2CID 206691291.</ref> The height of the troposphere varies with latitude, ranging between 8 km (5 mi) at the poles to 17 km (11 mi) at the equator, with some variation resulting from weather and seasonal factors.<ref name="geerts_linacre97" />

Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 Gya, forming the primarily nitrogen–oxygen atmosphere of today.<ref name="NYT-20131003" /> This change enabled the proliferation of aerobic organisms and, indirectly, the formation of the ozone layer due to the subsequent conversion of atmospheric O₂ into O₃. The ozone layer blocks ultraviolet solar radiation, permitting life on land.<ref name="Harrison 2002" /> Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature.<ref name="atmosphere" /> This last phenomenon is the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the surface, thereby raising the average temperature. Water vapor, carbon dioxide, methane, nitrous oxide, and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C (0 °F), in contrast to the current +15 °C (59 °F),<ref name="Pidwirny2006_7" /> and life on Earth probably would not exist in its current form.<ref name="Narottam2008" />

Weather and climate

The ITCZ's band of clouds over the Eastern Pacific and the Americas as seen from space

Worldwide Köppen climate classifications

Earth's atmosphere has no definite boundary, gradually becoming thinner and fading into outer space.<ref>Drake, Nadia (20 December 2018). "Where, exactly, is the edge of space? It depends on who you ask". National Geographic. Archived from the original on 4 March 2021. Retrieved 4 December 2021.</ref> Three-quarters of the atmosphere's mass is contained within the first 11 km (6.8 mi) of the surface; this lowest layer is called the troposphere.<ref>Erickson, Kristen; Doyle, Heather (28 June 2019). "Troposphere". SpacePlace. NASA. Retrieved 4 December 2021.</ref> Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower-density air then rises and is replaced by cooler, higher-density air. The result is atmospheric circulation that drives the weather and climate through redistribution of thermal energy.<ref name="moran2005" />

The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°.<ref name="berger2002" /> Ocean heat content and currents are also important factors in determining climate, particularly the thermohaline circulation that distributes thermal energy from the equatorial oceans to the polar regions.<ref name=rahmstorf2003 />

Earth receives 1361 W/m² of solar irradiance.<ref>"Earth Fact Sheet". NASA Space Science Data Coordinated Archive. 5 June 2023. Retrieved 17 September 2023.</ref><ref>Coddington, Odele; Lean, Judith L.; Pilewskie, Peter; Snow, Martin; Lindholm, Doug (2016). "A Solar Irradiance Climate Data Record". Bulletin of the American Meteorological Society. 97 (7): 1265–1282. Bibcode:2016BAMS...97.1265C. doi:10.1175/bams-d-14-00265.1.</ref> The amount of solar energy that reaches Earth's surface decreases with increasing latitude. At higher latitudes, the sunlight reaches the surface at lower angles, and it must pass through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level decreases by about 0.4 °C (0.7 °F) per degree of latitude from the equator.<ref name="sadava_heller2006" /> Earth's surface can be subdivided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, temperate and polar climates.<ref name="climate_zones" />

Further factors that affect a location's climates are its proximity to oceans, the oceanic and atmospheric circulation, and topology.<ref>Rohli, Robert. V.; Vega, Anthony J. (2018). Climatology (fourth ed.). Jones & Bartlett Learning. p. 49. ISBN 978-1-284-12656-3.</ref> Places close to oceans typically have colder summers and warmer winters, due to the fact that oceans can store large amounts of heat. The wind transports the cold or the heat of the ocean to the land.<ref>Rohli, Robert. V.; Vega, Anthony J. (2018). Climatology (fourth ed.). Jones & Bartlett Learning. p. 32. ISBN 978-1-284-12656-3.</ref> Atmospheric circulation also plays an important role: San Francisco and Washington DC are both coastal cities at about the same latitude. San Francisco's climate is significantly more moderate as the prevailing wind direction is from sea to land.<ref>Rohli, Robert. V.; Vega, Anthony J. (2018). Climatology (fourth ed.). Jones & Bartlett Learning. p. 34. ISBN 978-1-284-12656-3.</ref> Finally, temperatures decrease with height causing mountainous areas to be colder than low-lying areas.<ref>Rohli, Robert. V.; Vega, Anthony J. (2018). Climatology (fourth ed.). Jones & Bartlett Learning. p. 46. ISBN 978-1-284-12656-3.</ref>

Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and falls to the surface as precipitation.<ref name="moran2005" /> Most of the water is then transported to lower elevations by river systems and usually returned to the oceans or deposited into lakes. This water cycle is a vital mechanism for supporting life on land and is a primary factor in the erosion of surface features over geological periods. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topographic features, and temperature differences determine the average precipitation that falls in each region.<ref name="hydrologic_cycle" />

The commonly used Köppen climate classification system has five broad groups (humid tropics, arid, humid middle latitudes, continental and cold polar), which are further divided into more specific subtypes.<ref name="berger2002" /> The Köppen system rates regions based on observed temperature and precipitation.<ref>Rohli, Robert. V.; Vega, Anthony J. (2018). Climatology (fourth ed.). Jones & Bartlett Learning. p. 159. ISBN 978-1-284-12656-3.</ref> Surface air temperature can rise to around 55 °C (131 °F) in hot deserts, such as Death Valley, and can fall as low as −89 °C (−128 °F) in Antarctica.<ref>El Fadli, Khalid I.; et al. (2013). "World Meteorological Organization Assessment of the Purported World Record 58°C Temperature Extreme at El Azizia, Libya (13 September 1922)". Bulletin of the American Meteorological Society. 94 (2): 199–204. Bibcode:2013BAMS...94..199E. doi:10.1175/BAMS-D-12-00093.1. ISSN 0003-0007.</ref><ref>Turner, John; et al. (2009). "Record low surface air temperature at Vostok station, Antarctica". Journal of Geophysical Research: Atmospheres. 114 (D24): D24102. Bibcode:2009JGRD..11424102T. doi:10.1029/2009JD012104. ISSN 2156-2202.</ref>

Upper atmosphere

The upper atmosphere, the atmosphere above the troposphere,<ref>Morton, Oliver (26 August 2022). "Upper atmosphere Definition und Bedeutung". Collins Wörterbuch (in Deutsch). Retrieved 26 August 2022.</ref> is usually divided into the stratosphere, mesosphere, and thermosphere.<ref name="atmosphere" /> Each layer has a different lapse rate, defining the rate of change in temperature with height. Beyond these, the exosphere thins out into the magnetosphere, where the geomagnetic fields interact with the solar wind.<ref name=sciweek2004 /> Within the stratosphere is the ozone layer, a component that partially shields the surface from ultraviolet light and thus is important for life on Earth. The Kármán line, defined as 100 km (62 mi) above Earth's surface, is a working definition for the boundary between the atmosphere and outer space.<ref name=cordoba2004 />

Thermal energy causes some of the molecules at the outer edge of the atmosphere to increase their velocity to the point where they can escape from Earth's gravity. This causes a slow but steady loss of the atmosphere into space. Because unfixed hydrogen has a low molecular mass, it can achieve escape velocity more readily, and it leaks into outer space at a greater rate than other gases.<ref name="jas31_4_1118" /> The leakage of hydrogen into space contributes to the shifting of Earth's atmosphere and surface from an initially reducing state to its current oxidizing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is thought to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere.<ref name="sci293_5531_839" /> Hence the ability of hydrogen to escape from the atmosphere may have influenced the nature of life that developed on Earth.<ref name="abedon1997" /> In the current, oxygen-rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.<ref name="arwps4_265" />

Life on Earth

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

Earth's life has been shaping and inhabiting many particular ecosystems on Earth and has eventually expanded globally forming an overarching biosphere.<ref>Rutledge, Kim; et al. (24 June 2011). "Biosphere". National Geographic. Retrieved 1 November 2020.</ref> Therefore, life has impacted Earth, significantly altering Earth's atmosphere and surface over long periods of time, causing changes like the Great Oxidation Event.<ref>"NASA Astrobiology Institute". astrobiology.nasa.gov. Retrieved 9 November 2023.</ref>

Earth's life has over time greatly diversified, allowing the biosphere to have different biomes, which are inhabited by comparatively similar plants and animals.<ref>"Interdependency between animal and plant species". BBC Bitesize. BBC. p. 3. Retrieved 28 June 2019.</ref> The different biomes developed at distinct elevations or water depths, planetary temperature latitudes and on land also with different humidity. Earth's species diversity and biomass reaches a peak in shallow waters and with forests, particularly in equatorial, warm and humid conditions. While freezing polar regions and high altitudes, or extremely arid areas are relatively barren of plant and animal life.<ref name="amnat163_2_192" />

Earth provides liquid water—an environment where complex organic molecules can assemble and interact, and sufficient energy to sustain a metabolism.<ref name="ab2003" /> Plants and other organisms take up nutrients from water, soils and the atmosphere. These nutrients are constantly recycled between different species.<ref>Singh, J. S.; Singh, S. P.; Gupta, S.R. (2013). Ecology environmental science and conservation (First ed.). New Delhi: S. Chand & Company. ISBN 978-93-83746-00-2. OCLC 896866658.</ref>

Extreme weather, such as tropical cyclones (including hurricanes and typhoons), occurs over most of Earth's surface and has a large impact on life in those areas. From 1980 to 2000, these events caused an average of 11,800 human deaths per year.<ref>Smith, Sharon; Fleming, Lora; Solo-Gabriele, Helena; Gerwick, William H. (2011). Oceans and Human Health. Elsevier Science. p. 212. ISBN 978-0-08-087782-2.</ref> Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, blizzards, floods, droughts, wildfires, and other calamities and disasters.<ref>Alexander, David (1993). Natural Disasters. Springer Science & Business Media. p. 3. ISBN 978-1-317-93881-1.</ref> Human impact is felt in many areas due to pollution of the air and water, acid rain, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion and erosion.<ref>Goudie, Andrew (2000). The Human Impact on the Natural Environment. MIT Press. pp. 52, 66, 69, 137, 142, 185, 202, 355, 366. ISBN 978-0-262-57138-8.</ref> Human activities release greenhouse gases into the atmosphere which cause global warming.<ref name=ConsensusOnConsensus>Cook, John; Oreskes, Naomi; Doran, Peter T.; Anderegg, William R. L.; Verheggen, Bart; Maibach, Ed W; Carlton, J. Stuart; Lewandowsky, Stephan; Skuce, Andrew G.; Green, Sarah A.; Nuccitelli, Dana; Jacobs, Peter; Richardson, Mark; Winkler, Bärbel; Painting, Rob; Rice, Ken (2016). "Consensus on consensus: a synthesis of consensus estimates on human-caused global warming". Environmental Research Letters. 11 (4): 048002. Bibcode:2016ERL....11d8002C. doi:10.1088/1748-9326/11/4/048002. hdl:1983/34949783-dac1-4ce7-ad95-5dc0798930a6. ISSN 1748-9326.</ref> This is driving changes such as the melting of glaciers and ice sheets, a global rise in average sea levels, increased risk of drought and wildfires, and migration of species to colder areas.<ref name="Global Warming Effects">"Global Warming Effects". National Geographic. 14 January 2019. Archived from the original on 18 January 2017. Retrieved 16 September 2020.</ref>

Human geography

Originating from earlier primates in Eastern Africa 300,000 years ago humans have since been migrating and with the advent of agriculture in the 10th millennium BC increasingly settling Earth's land.<ref>"Introduction to Human Evolution | The Smithsonian Institution's Human Origins Program". humanorigins.si.edu. 11 July 2022. Retrieved 9 November 2023.</ref> In the 20th century Antarctica had been the last continent to see a first and until today limited human presence.

Human population has since the 19th century grown exponentially to seven billion in the early 2010s,<ref>Gomez, Jim; Sullivan, Tim (31 October 2011). "Various '7 billionth' babies celebrated worldwide". Yahoo News. Associated Press. Archived from the original on 31 October 2011. Retrieved 31 October 2011.</ref> and is projected to peak at around ten billion in the second half of the 21st century.<ref name="Harvey-2020">Harvey, Fiona (15 July 2020). "World population in 2100 could be 2 billion below UN forecasts, study suggests". The Guardian. ISSN 0261-3077. Retrieved 18 September 2020.</ref> Most of the growth is expected to take place in sub-Saharan Africa.<ref name="Harvey-2020" />

Distribution and density of human population varies greatly around the world with the majority living in south to eastern Asia and 90% inhabiting only the Northern Hemisphere of Earth,<ref>Lutz, Ashley (4 May 2012). "MAP OF THE DAY: Pretty Much Everyone Lives In The Northern Hemisphere". Business Insider. Retrieved 5 January 2019.</ref> partly due to the hemispherical predominance of the world's land mass, with 68% of the world's land mass being in the Northern Hemisphere.<ref>Méndez, Abel (6 July 2011). "Distribution of landmasses of the Paleo-Earth". University of Puerto Rico at Arecibo. Archived from the original on 6 January 2019. Retrieved 5 January 2019.</ref> Furthermore, since the 19th century humans have increasingly converged into urban areas with the majority living in urban areas by the 21st century.<ref name="OWID_urbanization_2019" />

Beyond Earth's surface humans have lived on a temporary basis, with only special purpose deep underground and underwater presence, and a few space stations. Human population virtually completely remains on Earth's surface, fully depending on Earth and the environment it sustains. Since the second half of the 20th century, some hundreds of humans have temporarily stayed beyond Earth, a tiny fraction of whom have reached another celestial body, the Moon.<ref name="shayler_vis2005" /><ref>Holmes, Oliver (19 November 2018). "Space: how far have we gone – and where are we going?". The Guardian. ISSN 0261-3077. Retrieved 10 October 2020.</ref>

Earth has been subject to extensive human settlement, and humans have developed diverse societies and cultures. Most of Earth's land has been territorially claimed since the 19th century by sovereign states (countries) separated by political borders, and 205 such states exist today,<ref>"Member States | United Nations". United Nations. Archived from the original on 1 March 2023. Retrieved 3 January 2024.</ref> with only parts of Antarctica and a few small regions remaining unclaimed.<ref>Lloyd, John; Mitchinson, John (2010). The Discretely Plumper Second QI Book of General Ignorance. Faber & Faber. pp. 116–117. ISBN 978-0-571-29072-7.</ref> Most of these states together form the United Nations, the leading worldwide intergovernmental organization,<ref>Smith, Courtney B. (2006). Politics and Process at the United Nations: The Global Dance (PDF). Lynne Reiner. pp. 1–4. ISBN 978-1-58826-323-0.</ref> which extends human governance over the ocean and Antarctica, and therefore all of Earth.

Natural resources and land use

Earth has resources that have been exploited by humans.<ref>"What are the consequences of the overexploitation of natural resources?". Iberdrola. Retrieved 28 June 2019.</ref> Those termed non-renewable resources, such as fossil fuels, are only replenished over geological timescales.<ref>"13. Exploitation of Natural Resources". European Environment Agency. European Union. 20 April 2016. Retrieved 28 June 2019.</ref> Large deposits of fossil fuels are obtained from Earth's crust, consisting of coal, petroleum, and natural gas.<ref>Huebsch, Russell (29 September 2017). "How Are Fossil Fuels Extracted From the Ground?". Sciencing. Leaf Group Media. Retrieved 28 June 2019.</ref> These deposits are used by humans both for energy production and as feedstock for chemical production.<ref>"Electricity generation – what are the options?". World Nuclear Association. Retrieved 28 June 2019.</ref> Mineral ore bodies have also been formed within the crust through a process of ore genesis, resulting from actions of magmatism, erosion, and plate tectonics.<ref>Brimhall, George (May 1991). "The Genesis of Ores". Scientific American. Nature America. 264 (5): 84–91. Bibcode:1991SciAm.264e..84B. doi:10.1038/scientificamerican0591-84. JSTOR 24936905. Retrieved 13 October 2020.</ref> These metals and other elements are extracted by mining, a process which often brings environmental and health damage.<ref>Lunine, Jonathan I. (2013). Earth: Evolution of a Habitable World (second ed.). Cambridge University Press. pp. 292–294. ISBN 978-0-521-61519-8.</ref>

Earth's biosphere produces many useful biological products for humans, including food, wood, pharmaceuticals, oxygen, and the recycling of organic waste. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends on dissolved nutrients washed down from the land.<ref name="science299_5607_673" /> In 2019, 39 million km² (15 million sq mi) of Earth's land surface consisted of forest and woodlands, 12 million km² (4.6 million sq mi) was shrub and grassland, 40 million km² (15 million sq mi) were used for animal feed production and grazing, and 11 million km² (4.2 million sq mi) were cultivated as croplands.<ref name="OWID_2019" /> Of the 12–14% of ice-free land that is used for croplands, 2 percentage points were irrigated in 2015.<ref>IPCC (2019). "Summary for Policymakers" (PDF). IPCC Special Report on Climate Change and Land. p. 8.</ref> Humans use building materials to construct shelters.<ref>Tate, Nikki; Tate-Stratton, Dani (2014). Take Shelter: At Home Around the World. Orca Book Publishers. p. 6. ISBN 978-1-4598-0742-6.</ref>

Humans and the environment

Human activities have impacted Earth's environments. Through activities such as the burning of fossil fuels, humans have been increasing the amount of greenhouse gases in the atmosphere, altering Earth's energy budget and climate.<ref name=ConsensusOnConsensus /><ref>Lindsey, Rebecca (14 January 2009). "Climate and Earth's Energy Budget". Earth Observatory. NASA. Retrieved 19 December 2021.</ref> It is estimated that global temperatures in the year 2020 were 1.2 °C (2.2 °F) warmer than the preindustrial baseline.<ref>"The State of the Global Climate 2020". World Meteorological Organization. 14 January 2021. Archived from the original on 29 November 2023. Retrieved 3 March 2021.</ref> This increase in temperature, known as global warming, has contributed to the melting of glaciers, rising sea levels, increased risk of drought and wildfires, and migration of species to colder areas.<ref name="Global Warming Effects" />

The concept of planetary boundaries was introduced to quantify humanity's impact on Earth. Of the nine identified boundaries, five have been crossed: Biosphere integrity, climate change, chemical pollution, destruction of wild habitats and the nitrogen cycle are thought to have passed the safe threshold.<ref name="Boundaries">DiGirolamo, Mike (8 September 2021). "We've crossed four of nine planetary boundaries. What does this mean?". Mongabay. Retrieved 27 January 2022.</ref><ref>Carrington, Damien (18 January 2022). "Chemical pollution has passed safe limit for humanity, say scientists". The Guardian.</ref> As of 2018, no country meets the basic needs of its population without transgressing planetary boundaries. It is thought possible to provide all basic physical needs globally within sustainable levels of resource use.<ref>O'Neill, Daniel W.; Fanning, Andrew L.; Lamb, William F.; Steinberger, Julia K. (2018). "A good life for all within planetary boundaries". Nature Sustainability. 1 (2): 88–95. Bibcode:2018NatSu...1...88O. doi:10.1038/s41893-018-0021-4. ISSN 2398-9629. S2CID 169679920.</ref>

Cultural and historical viewpoint

Human cultures have developed many views of the planet.<ref name="NYT-20181224b">Widmer, Ted (24 December 2018). "What Did Plato Think the Earth Looked Like? – For millenniums, humans have tried to imagine the world in space. Fifty years ago, we finally saw it". The New York Times. Archived from the original on 1 January 2022. Retrieved 25 December 2018.</ref> The standard astronomical symbols of Earth are a quartered circle, ,<ref name="liungman2004" /> representing the four corners of the world, and a globus cruciger, . Earth is sometimes personified as a deity. In many cultures it is a mother goddess that is also the primary fertility deity.<ref name="Stookey-2004">Stookey, Lorena Laura (2004). Thematic Guide to World Mythology. Westport, CN: Greenwood Press. pp. 114–115. ISBN 978-0-313-31505-3.</ref> Creation myths in many religions involve the creation of Earth by a supernatural deity or deities.<ref name="Stookey-2004" /> The Gaia hypothesis, developed in the mid-20th century, compared Earth's environments and life as a single self-regulating organism leading to broad stabilization of the conditions of habitability.<ref>Lovelock, James E. (2009). The Vanishing Face of Gaia. Basic Books. p. 255. ISBN 978-0-465-01549-8.</ref><ref>Lovelock, James E. (1972). "Gaia as seen through the atmosphere". Atmospheric Environment. 6 (8): 579–580. Bibcode:1972AtmEn...6..579L. doi:10.1016/0004-6981(72)90076-5. ISSN 1352-2310.</ref><ref>Lovelock, J.E.; Margulis, L. (1974). "Atmospheric homeostasis by and for the biosphere: the gaia hypothesis". Tellus A. 26 (1–2): 2–10. Bibcode:1974Tell...26....2L. doi:10.3402/tellusa.v26i1-2.9731. S2CID 129803613.</ref>

Images of Earth taken from space, particularly during the Apollo program, have been credited with altering the way that people viewed the planet that they lived on, called the overview effect, emphasizing its beauty, uniqueness and apparent fragility.<ref>Overbye, Dennis (21 December 2018). "Apollo 8's Earthrise: The Shot Seen Round the World – Half a century ago today, a photograph from the moon helped humans rediscover Earth". The New York Times. Archived from the original on 1 January 2022. Retrieved 24 December 2018.</ref><ref>Boulton, Matthew Myer; Heithaus, Joseph (24 December 2018). "We Are All Riders on the Same Planet – Seen from space 50 years ago, Earth appeared as a gift to preserve and cherish. What happened?". The New York Times. Archived from the original on 1 January 2022. Retrieved 25 December 2018.</ref> In particular, this caused a realization of the scope of effects from human activity on Earth's environment. Enabled by science, particularly Earth observation,<ref>"ESPI Evening Event "Seeing Our Planet Whole: A Cultural and Ethical View of Earth Observation"". ESPI – European Space Policy Institute. 7 October 2021. Retrieved 27 January 2022.</ref> humans have started to take action on environmental issues globally,<ref>"Two early images of Earth that bolstered the environmental movement – CBC Radio". CBC. 16 April 2020. Retrieved 27 January 2022.</ref> acknowledging the impact of humans and the interconnectedness of Earth's environments.

Scientific investigation has resulted in several culturally transformative shifts in people's view of the planet. Initial belief in a flat Earth was gradually displaced in Ancient Greece by the idea of a spherical Earth, which was attributed to both the philosophers Pythagoras and Parmenides.<ref>Kahn, Charles H. (2001). Pythagoras and the Pythagoreans: A Brief History. Indianapolis, IN and Cambridge, England: Hackett Publishing Company. p. 53. ISBN 978-0-87220-575-8.</ref><ref>Garwood, Christine (2008). Flat earth : the history of an infamous idea (1st ed.). New York: Thomas Dunne Books. pp. 26–31. ISBN 978-0-312-38208-7. OCLC 184822945.</ref> Earth was generally believed to be the center of the universe until the 16th century, when scientists first concluded that it was a moving object, one of the planets of the Solar System.<ref name="arnett20060716" />

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

Notes

<references group="n" responsive="0"><ref name="Aoki">The ultimate source of these figures, uses the term "seconds of UT1" instead of "seconds of mean solar time".—Aoki, S.; Kinoshita, H.; Guinot, B.; Kaplan, G. H.; McCarthy, D. D.; Seidelmann, P. K. (1982). "The new definition of universal time". Astronomy and Astrophysics. 105 (2): 359–361. Bibcode:1982A&A...105..359A.</ref>

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

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

<ref name="hill_radius">For Earth, the Hill radius is <math>R_H = a\left ( \frac{m}{3M} \right )^{\frac{1}{3</references>

</math>, where m is the mass of Earth, a is an astronomical unit, and M is the mass of the Sun. So the radius in AU is about <math>\left ( \frac{1}{3 \cdot 332,946} \right )^{\frac{1}{3}} = 0.01</math>.</ref>

<ref name="jaes41_3_379">Including the Somali Plate, which is being formed out of the African Plate. See: Chorowicz, Jean (October 2005). "The East African rift system". Journal of African Earth Sciences. 43 (1–3): 379–410. Bibcode:2005JAfES..43..379C. doi:10.1016/j.jafrearsci.2005.07.019.</ref>

<ref name="solar_energy">Aphelion is 103.4% of the distance to perihelion. Due to the inverse square law, the radiation at perihelion is about 106.9% of the energy at aphelion.</ref>

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

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

}}

References

<references group="" responsive="1"><ref name="aaa428_261">Laskar, J.; et al. (2004). "A long-term numerical solution for the insolation quantities of the Earth". Astronomy and Astrophysics. 428 (1): 261–285. Bibcode:2004A&A...428..261L. doi:10.1051/0004-6361:20041335.</ref>

<ref name="ab2003">Staff (September 2003). "Astrobiology Roadmap". NASA, Lockheed Martin. Archived from the original on 12 March 2012. Retrieved 10 March 2007.</ref>

<ref name="abedon1997">Abedon, Stephen T. (31 March 1997). "History of Earth". Ohio State University. Archived from the original on 29 November 2012. Retrieved 19 March 2007.</ref>

<ref name="age_earth1">See:

Dalrymple, G. Brent (1991). The Age of the Earth. California: Stanford University Press. ISBN 978-0-8047-1569-0.
Newman, William L. (9 July 2007). "Age of the Earth". Publications Services, USGS. Retrieved 20 September 2007.
Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Geological Society, London, Special Publications. 190 (1): 205–221. Bibcode:2001GSLSP.190..205D. doi:10.1144/GSL.SP.2001.190.01.14. S2CID 130092094. Retrieved 20 September 2007.</ref>

<ref name="aj136_5_1906">McCarthy, Dennis D.; Hackman, Christine; Nelson, Robert A. (November 2008). "The Physical Basis of the Leap Second". The Astronomical Journal. 136 (5): 1906–1908. Bibcode:2008AJ....136.1906M. doi:10.1088/0004-6256/136/5/1906.</ref>

<ref name="ajes38_613">Armstrong, R. L. (1991). "The persistent myth of crustal growth" (PDF). Australian Journal of Earth Sciences. 38 (5): 613–630. Bibcode:1991AuJES..38..613A. CiteSeerX 10.1.1.527.9577. doi:10.1080/08120099108727995.</ref>

<ref name="Allen294">Allen, Clabon Walter; Cox, Arthur N. (2000). Arthur N. Cox (ed.). Allen's Astrophysical Quantities. Springer. p. 294. ISBN 978-0-387-98746-0. Retrieved 13 March 2011.</ref>

<ref name="Allen296">Allen, Clabon Walter; Cox, Arthur N. (2000). Arthur N. Cox (ed.). Allen's Astrophysical Quantities. Springer. p. 296. ISBN 978-0-387-98746-0. Retrieved 17 August 2010.</ref>

<ref name="amnat163_2_192">Hillebrand, Helmut (2004). "On the Generality of the Latitudinal Gradient" (PDF). American Naturalist. 163 (2): 192–211. doi:10.1086/381004. PMID 14970922. S2CID 9886026.</ref>

<ref name="angular">Williams, David R. (10 February 2006). "Planetary Fact Sheets". NASA. See the apparent diameters on the Sun and Moon pages. Retrieved 28 September 2008.</ref> <ref name="arnett20060716">Arnett, Bill (16 July 2006). "Earth". The Nine Planets, A Multimedia Tour of the Solar System: one star, eight planets, and more. Retrieved 9 March 2010.</ref>

<ref name="arwps4_265">Hunten, D. M.; Donahue, T. M (1976). "Hydrogen loss from the terrestrial planets". Annual Review of Earth and Planetary Sciences. 4 (1): 265–292. Bibcode:1976AREPS...4..265H. doi:10.1146/annurev.ea.04.050176.001405.</ref>

<ref name="asp2002">Guinan, E. F.; Ribas, I. (2002). Benjamin Montesinos, Alvaro Gimenez and Edward F. Guinan (ed.). Our Changing Sun: The Role of Solar Nuclear Evolution and Magnetic Activity on Earth's Atmosphere and Climate. ASP Conference Proceedings: The Evolving Sun and its Influence on Planetary Environments. San Francisco: Astronomical Society of the Pacific. Bibcode:2002ASPC..269...85G. ISBN 978-1-58381-109-2.</ref>

<ref name="asu_highest_temp">"World: Highest Temperature". WMO Weather and Climate Extremes Archive. Arizona State University. Retrieved 6 September 2020.</ref>

<ref name="asu_lowest_temp">"World: Lowest Temperature". WMO Weather and Climate Extremes Archive. Arizona State University. Retrieved 6 September 2020.</ref>

<ref name="atmosphere">Staff (8 October 2003). "Earth's Atmosphere". NASA. Archived from the original on 27 April 2020. Retrieved 21 March 2007.</ref>

<ref name="berger2002">Berger, Wolfgang H. (2002). "The Earth's Climate System". University of California, San Diego. Retrieved 24 March 2007.</ref>

<ref name="bgsa119_1_140">Wilkinson, B. H.; McElroy, B. J. (2007). "The impact of humans on continental erosion and sedimentation". Bulletin of the Geological Society of America. 119 (1–2): 140–156. Bibcode:2007GSAB..119..140W. doi:10.1130/B25899.1. S2CID 128776283.</ref> <ref name="bouvier_wadhwa2010">Bouvier, Audrey; Wadhwa, Meenakshi (September 2010). "The age of the Solar System redefined by the oldest Pb–Pb age of a meteoritic inclusion". Nature Geoscience. 3 (9): 637–641. Bibcode:2010NatGe...3..637B. doi:10.1038/ngeo941.</ref>

<ref name="bradley_2011">Bradley, D.C. (2011). "Secular Trends in the Geologic Record and the Supercontinent Cycle". Earth-Science Reviews. 108 (1–2): 16–33. Bibcode:2011ESRv..108...16B. CiteSeerX 10.1.1.715.6618. doi:10.1016/j.earscirev.2011.05.003. S2CID 140601854.</ref>

<ref name="britt2000">Britt, Robert (25 February 2000). "Freeze, Fry or Dry: How Long Has the Earth Got?". Space.com. Archived from the original on 5 June 2009.</ref>

<ref name=bromberg2008>Bromberg, Irv (1 May 2008). "The Lengths of the Seasons (on Earth)". Sym545. University of Toronto. Archived from the original on 18 December 2008. Retrieved 8 November 2008.</ref>

<ref name="brown_mussett1981">Brown, Geoff C.; Mussett, Alan E. (1981). The Inaccessible Earth (2nd ed.). Taylor & Francis. p. 166. ISBN 978-0-04-550028-4. Note: After Ronov and Yaroshevsky (1969).</ref>

<ref name="brown_wohletz2005">Brown, W. K.; Wohletz, K. H. (2005). "SFT and the Earth's Tectonic Plates". Los Alamos National Laboratory. Retrieved 2 March 2007.</ref>

<ref name="burton20021129">Burton, Kathleen (29 November 2002). "Astrobiologists Find Evidence of Early Life on Land". NASA. Archived from the original on 11 October 2011. Retrieved 5 March 2007.</ref>

<ref name=campbelwh>Campbell, Wallace Hall (2003). Introduction to Geomagnetic Fields. New York: Cambridge University Press. p. 57. ISBN 978-0-521-82206-0.</ref>

<ref name=canup_asphaug2001b>Canup, R.; Asphaug, E. I. (2001). "Origin of the Moon in a giant impact near the end of the Earth's formation". Nature. 412 (6848): 708–712. Bibcode:2001Natur.412..708C. doi:10.1038/35089010. PMID 11507633. S2CID 4413525.</ref>

<ref name=cazenave_ahrens1995>Cazenave, Anny (1995). "Geoid, Topography and Distribution of Landforms" (PDF). In Ahrens, Thomas J (ed.). Global Earth Physics: A Handbook of Physical Constants. AGU Reference Shelf. Vol. 1. Washington, DC: American Geophysical Union. Bibcode:1995geph.conf.....A. doi:10.1029/RF001. ISBN 978-0-87590-851-9. Archived from the original (PDF) on 16 October 2006. Retrieved 3 August 2008.</ref>

<ref name=Choi>Choi, Charles Q. (27 July 2011). "First Asteroid Companion of Earth Discovered at Last". Space.com. Retrieved 27 July 2011.</ref>

<ref name=christou_asher2011>Christou, Apostolos A.; Asher, David J. (31 March 2011). "A long-lived horseshoe companion to the Earth". Monthly Notices of the Royal Astronomical Society. 414 (4): 2965–2969. arXiv:1104.0036. Bibcode:2011MNRAS.414.2965C. doi:10.1111/j.1365-2966.2011.18595.x. S2CID 13832179. See table 2, p. 5.</ref>

<ref name=climate_zones>Staff. "Climate Zones". UK Department for Environment, Food and Rural Affairs. Archived from the original on 8 August 2010. Retrieved 24 March 2007.</ref>

<ref name=cmp134_3>Bowring, Samuel A.; Williams, Ian S. (1999). "Priscoan (4.00–4.03 Ga) orthogneisses from northwestern Canada". Contributions to Mineralogy and Petrology. 134 (1): 3–16. Bibcode:1999CoMP..134....3B. doi:10.1007/s004100050465. S2CID 128376754.</ref>

<ref name=cordoba2004>de Córdoba, S. Sanz Fernández (21 June 2004). "Presentation of the Karman separation line, used as the boundary separating Aeronautics and Astronautics". Fédération Aéronautique Internationale. Archived from the original on 15 January 2010. Retrieved 21 April 2007.</ref>

<ref name="Cox2000">Allen, Clabon Walter; Cox, Arthur N. (2000). Arthur N. Cox (ed.). Allen's Astrophysical Quantities (4th ed.). New York: AIP Press. p. 244. ISBN 978-0-387-98746-0. Retrieved 17 August 2010.</ref>

<ref name="Deuss_2014">Deuss, Arwen (2014). "Heterogeneity and Anisotropy of Earth's Inner Core". Annu. Rev. Earth Planet. Sci. 42 (1): 103–126. Bibcode:2014AREPS..42..103D. doi:10.1146/annurev-earth-060313-054658.</ref>

<ref name="Dhuime_etal_2018">Dhuime, B.; Hawksworth, C.J.; Delavault, H.; Cawood, P.A. (2018). "Rates of generation and destruction of the continental crust: implications for continental growth". Philosophical Transactions A. 376 (2132). Bibcode:2018RSPTA.37670403D. doi:10.1098/rsta.2017.0403. PMC 6189557. PMID 30275156.</ref> <ref name=duennebier1999>Duennebier, Fred (12 August 1999). "Pacific Plate Motion". University of Hawaii. Retrieved 14 March 2007.</ref> <ref name="earth_fact_sheet">Williams, David R. (16 March 2017). "Earth Fact Sheet". NASA/Goddard Space Flight Center. Retrieved 26 July 2018.</ref>

<ref name=epsl121_1>Vlaar, N; Vankeken, P.; Vandenberg, A. (1994). "Cooling of the Earth in the Archaean: Consequences of pressure-release melting in a hotter mantle" (PDF). Earth and Planetary Science Letters. 121 (1–2): 1–18. Bibcode:1994E&PSL.121....1V. doi:10.1016/0012-821X(94)90028-0. Archived from the original (PDF) on 19 March 2012.</ref>

<ref name="espenak_meeus20070207">Espenak, Fred; Meeus, Jean (7 February 2007). "Secular acceleration of the Moon". NASA. Archived from the original on 2 March 2008. Retrieved 20 April 2007.</ref>

<ref name="fisher19960205">Fisher, Rick (5 February 1996). "Earth Rotation and Equatorial Coordinates". National Radio Astronomy Observatory. Archived from the original on 18 August 2011. Retrieved 21 March 2007.</ref>

<ref name=fitzpatrick2006>Fitzpatrick, Richard (16 February 2006). "MHD dynamo theory". NASA WMAP. Retrieved 27 February 2007.</ref> <ref name="geerts_linacre97">Geerts, B.; Linacre, E. (November 1997). "The height of the tropopause". Resources in Atmospheric Sciences. University of Wyoming. Retrieved 10 August 2006.</ref>

<ref name="GeolSoc">"The Crust and Lithosphere". London Geological Society. 2012. Retrieved 25 October 2020.</ref>

<ref name=gould1994>Gould, Stephen J. (October 1994). "The Evolution of Life on Earth". Scientific American. 271 (4): 84–91. Bibcode:1994SciAm.271d..84G. doi:10.1038/scientificamerican1094-84. PMID 7939569. Retrieved 5 March 2007.</ref>

<ref name="Harrison 2002">Harrison, Roy M.; Hester, Ronald E. (2002). Causes and Environmental Implications of Increased UV-B Radiation. Royal Society of Chemistry. ISBN 978-0-85404-265-4.</ref>

<ref name="hbcp2000">Various (2000). David R. Lide (ed.). Handbook of Chemistry and Physics (81st ed.). CRC Press. ISBN 978-0-8493-0481-1.</ref>

<ref name="heat loss">Sclater, John G; Parsons, Barry; Jaupart, Claude (1981). "Oceans and Continents: Similarities and Differences in the Mechanisms of Heat Loss". Journal of Geophysical Research. 86 (B12): 11535. Bibcode:1981JGR....8611535S. doi:10.1029/JB086iB12p11535.</ref>

<ref name=hess5_4_569>Bounama, Christine; Franck, S.; Von Bloh, W. (2001). "The fate of Earth's ocean". Hydrology and Earth System Sciences. 5 (4): 569–575. Bibcode:2001HESS....5..569B. doi:10.5194/hess-5-569-2001. S2CID 14024675.</ref> <ref name=hydrologic_cycle>Various (21 July 1997). "The Hydrologic Cycle". University of Illinois. Retrieved 24 March 2007.</ref>

<ref name="IERS2004">International Earth Rotation and Reference Systems Service (IERS) Working Group (2004). "General Definitions and Numerical Standards" (PDF). In McCarthy, Dennis D.; Petit, Gérard (eds.). IERS Conventions (2003) (PDF). Frankfurt am Main: Verlag des Bundesamts für Kartographie und Geodäsie. p. 12. ISBN 978-3-89888-884-4. Retrieved 29 April 2016.</ref>

<ref name=IERS>Staff (13 March 2021). "Useful Constants". International Earth Rotation and Reference Systems Service. Retrieved 8 June 2022.</ref>

<ref name=jas22_3_225>Berkner, L. V.; Marshall, L. C. (1965). "On the Origin and Rise of Oxygen Concentration in the Earth's Atmosphere". Journal of the Atmospheric Sciences. 22 (3): 225–261. Bibcode:1965JAtS...22..225B. doi:10.1175/1520-0469(1965)022<0225:OTOARO>2.0.CO;2.</ref>

<ref name=jas31_4_1118>Liu, S. C.; Donahue, T. M. (1974). "The Aeronomy of Hydrogen in the Atmosphere of the Earth". Journal of the Atmospheric Sciences. 31 (4): 1118–1136. Bibcode:1974JAtS...31.1118L. doi:10.1175/1520-0469(1974)031<1118:TAOHIT>2.0.CO;2.</ref>

<ref name=jessey>Jessey, David. "Weathering and Sedimentary Rocks". California State Polytechnic University, Pomona. Archived from the original on 3 July 2007. Retrieved 20 March 2007.</ref>

<ref name=jg31_3_267>Pollack, Henry N.; Hurter, Suzanne J.; Johnson, Jeffrey R. (August 1993). "Heat flow from the Earth's interior: Analysis of the global data set". Reviews of Geophysics. 31 (3): 267–280. Bibcode:1993RvGeo..31..267P. doi:10.1029/93RG01249.</ref>

<ref name=kennish2001>Kennish, Michael J. (2001). Practical handbook of marine science. Marine science series (3rd ed.). Boca Raton, Florida: CRC Press. p. 35. doi:10.1201/9781420038484. ISBN 978-0-8493-2391-1.</ref>

<ref name=kious_tilling1999>Kious, W. J.; Tilling, R. I. (5 May 1999). "Understanding plate motions". USGS. Retrieved 2 March 2007.</ref>

<ref name=kring>Kring, David A. "Terrestrial Impact Cratering and Its Environmental Effects". Lunar and Planetary Laboratory. Retrieved 22 March 2007.</ref>

<ref name=layers_earth>Staff. "Layers of the Earth". Volcano World. Oregon State University. Archived from the original on 11 February 2013. Retrieved 11 March 2007.</ref>

<ref name=lin2006>Lin, Haosheng (2006). "Animation of precession of moon orbit". Survey of Astronomy AST110-6. University of Hawaii at Manoa. Retrieved 10 September 2010.</ref>

<ref name=liungman2004>Liungman, Carl G. (2004). "Group 29: Multi-axes symmetric, both soft and straight-lined, closed signs with crossing lines". Symbols – Encyclopedia of Western Signs and Ideograms. New York: Ionfox AB. pp. 281–282. ISBN 978-91-972705-0-2.</ref>

<ref name=michon2006>Scott, Michon (24 April 2006). "Earth's Big heat Bucket". NASA Earth Observatory. Retrieved 14 March 2007.</ref>

<ref name=milbert_smith96>Milbert, D. G.; Smith, D. A. "Converting GPS Height into NAVD88 Elevation with the GEOID96 Geoid Height Model". National Geodetic Survey, NOAA. Retrieved 7 March 2007.</ref>

<ref name="moon_fact_sheet">Williams, David R. (1 September 2004). "Moon Fact Sheet". NASA. Retrieved 21 March 2007.</ref>

<ref name="moran2005">Moran, Joseph M. (2005). "Weather". World Book Online Reference Center. NASA/World Book, Inc. Archived from the original on 13 December 2010. Retrieved 17 March 2007.</ref>

<ref name=mullen2002>Mullen, Leslie (11 June 2002). "Salt of the Early Earth". NASA Astrobiology Magazine. Archived from the original on 30 June 2007. Retrieved 14 March 2007.</ref> <ref name=nasa20051201>Astrophysicist team (1 December 2005). "Earth's location in the Milky Way". NASA. Archived from the original on 1 July 2008. Retrieved 11 June 2008.</ref>

<ref name=natsci_oxy4>Morris, Ron M. "Oceanic Processes". NASA Astrobiology Magazine. Archived from the original on 15 April 2009. Retrieved 14 March 2007.</ref>

<ref name="ngdc2006">Sandwell, D. T.; Smith, Walter H. F. (7 July 2006). "Exploring the Ocean Basins with Satellite Altimeter Data". NOAA/NGDC. Archived from the original on 15 July 2014. Retrieved 21 April 2007.</ref>

<ref name="NIST2008">The international system of units (SI) (PDF) (2008 ed.). United States Department of Commerce, NIST Special Publication 330. p. 52. Archived from the original (PDF) on 5 February 2009.</ref>

<ref name=noaa20070307>Mueller, R. D.; et al. (7 March 2007). "Age of the Ocean Floor Poster". NOAA. Retrieved 14 March 2007.</ref>

<ref name=ocean23_2_112>Charette, Matthew A.; Smith, Walter H. F. (June 2010). "The Volume of Earth's Ocean". Oceanography. 23 (2): 112–114. doi:10.5670/oceanog.2010.51. hdl:1912/3862.</ref>

<ref name="OWID_2019">Ritchie, H.; Roser, M. (2019). "Land Use". Our World in Data. Retrieved 26 October 2020.</ref>

<ref name="OWID_urbanization_2019">Ritchie, H.; Roser, M. (2019). "What share of people will live in urban areas in the future?". Our World in Data. Retrieved 26 October 2020.</ref>

<ref name=physorg20100304>Staff (4 March 2010). "Oldest measurement of Earth's magnetic field reveals battle between Sun and Earth for our atmosphere". Phys.org. Retrieved 27 March 2010.</ref>

<ref name="Pidwirny 2006_8">Pidwirny, Michael (2 February 2006). "Surface area of our planet covered by oceans and continents.(Table 8o-1)". University of British Columbia, Okanagan. Retrieved 26 November 2007.</ref>

<ref name="Pidwirny2006_7">Pidwirny, Michael (2006). "Fundamentals of Physical Geography (2nd Edition)". University of British Columbia, Okanagan. Retrieved 19 March 2007.</ref>

<ref name=pnas1_24_9576>Li, King-Fai; Pahlevan, Kaveh; Kirschvink, Joseph L.; Yung, Yuk L. (2009). "Atmospheric pressure as a natural climate regulator for a terrestrial planet with a biosphere" (PDF). Proceedings of the National Academy of Sciences. 106 (24): 9576–9579. Bibcode:2009PNAS..106.9576L. doi:10.1073/pnas.0809436106. PMC 2701016. PMID 19487662. Retrieved 19 July 2009.</ref>

<ref name=pnas71_12_6973>Morgan, J. W.; Anders, E. (1980). "Chemical composition of Earth, Venus, and Mercury". Proceedings of the National Academy of Sciences. 77 (12): 6973–6977. Bibcode:1980PNAS...77.6973M. doi:10.1073/pnas.77.12.6973. PMC 350422. PMID 16592930.</ref>

<ref name=podp2000>Meschede, Martin; Barckhausen, Udo (20 November 2000). "Plate Tectonic Evolution of the Cocos-Nazca Spreading Center". Proceedings of the Ocean Drilling Program. Texas A&M University. Retrieved 2 April 2007.</ref>

<ref name=ps20_5_16>Senne, Joseph H. (2000). "Did Edmund Hillary Climb the Wrong Mountain". Professional Surveyor. 20 (5): 16–21. Archived from the original on 17 July 2015. Retrieved 16 July 2015.</ref>

<ref name=psc>Staff. "Paleoclimatology – The Study of Ancient Climates". Page Paleontology Science Center. Archived from the original on 4 March 2007. Retrieved 2 March 2007.</ref>

<ref name=ptrsl360_1795_1227>Alfè, D.; Gillan, M. J.; Vočadlo, L.; Brodholt, J.; Price, G. D. (2002). "The ab initio simulation of the Earth's core" (PDF). Philosophical Transactions of the Royal Society. 360 (1795): 1227–1244. Bibcode:2002RSPTA.360.1227A. doi:10.1098/rsta.2002.0992. PMID 12804276. S2CID 21132433. Retrieved 28 February 2007.</ref>

<ref name=rahmstorf2003>Rahmstorf, Stefan (2003). "The Thermohaline Ocean Circulation". Potsdam Institute for Climate Impact Research. Retrieved 21 April 2007.</ref>

<ref name=reilly20091022>Reilly, Michael (22 October 2009). "Controversial Moon Origin Theory Rewrites History". Discovery News. Archived from the original on 9 January 2010. Retrieved 30 January 2010.</ref>

<ref name=sa282_6_90>Doolittle, W. Ford; Worm, Boris (February 2000). "Uprooting the tree of life" (PDF). Scientific American. 282 (6): 90–95. Bibcode:2000SciAm.282b..90D. doi:10.1038/scientificamerican0200-90. PMID 10710791. Archived from the original (PDF) on 15 July 2011.</ref>

<ref name=sadava_heller2006>Sadava, David E.; Heller, H. Craig; Orians, Gordon H. (2006). Life, the Science of Biology (8th ed.). MacMillan. p. 1114. ISBN 978-0-7167-7671-0.</ref>

<ref name=sample2005>Sample, Sharron (21 June 2005). "Sea Surface Temperature". NASA. Archived from the original on 27 April 2013. Retrieved 21 April 2007.</ref>

<ref name=sanders20031210>Sanders, Robert (10 December 2003). "Radioactive potassium may be major heat source in Earth's core". UC Berkeley News. Retrieved 28 February 2007.</ref>

<ref name=sci293_5531_839>Catling, David C.; Zahnle, Kevin J.; McKay, Christopher P. (2001). "Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth". Science. 293 (5531): 839–843. Bibcode:2001Sci...293..839C. CiteSeerX 10.1.1.562.2763. doi:10.1126/science.1061976. PMID 11486082. S2CID 37386726.</ref>

<ref name=science164_1229>Hurley, P. M.; Rand, J. R. (June 1969). "Pre-drift continental nuclei". Science. 164 (3885): 1229–1242. Bibcode:1969Sci...164.1229H. doi:10.1126/science.164.3885.1229. PMID 17772560.</ref>

<ref name=science246_4926_103>Richards, M. A.; Duncan, R. A.; Courtillot, V. E. (1989). "Flood Basalts and Hot-Spot Tracks: Plume Heads and Tails". Science. 246 (4926): 103–107. Bibcode:1989Sci...246..103R. doi:10.1126/science.246.4926.103. PMID 17837768. S2CID 9147772.</ref>

<ref name=science299_5607_673>Rona, Peter A. (2003). "Resources of the Sea Floor". Science. 299 (5607): 673–674. doi:10.1126/science.1080679. PMID 12560541. S2CID 129262186.</ref>

<ref name=science310_5756_1947>Harrison, T. M.; Blichert-Toft, J.; Müller, W.; Albarede, F.; Holden, P.; Mojzsis, S. (December 2005). "Heterogeneous Hadean hafnium: evidence of continental crust at 4.4 to 4.5 ga". Science. 310 (5756): 1947–1950. Bibcode:2005Sci...310.1947H. doi:10.1126/science.1117926. PMID 16293721. S2CID 11208727.</ref>

<ref name=sciweek2004>Staff (2004). "Stratosphere and Weather; Discovery of the Stratosphere". Science Week. Archived from the original on 13 July 2007. Retrieved 14 March 2007.</ref> <ref name=seidelmann1992>Seidelmann, P. Kenneth (1992). Explanatory Supplement to the Astronomical Almanac. Mill Valley, CA: University Science Books. p. 48. ISBN 978-0-935702-68-2.</ref>

<ref name=seligman2008>Seligman, Courtney (2008). "The Structure of the Terrestrial Planets". Online Astronomy eText Table of Contents. cseligman.com. Retrieved 28 February 2008.</ref>

<ref name=shayler_vis2005>Shayler, David; Vis, Bert (2005). Russia's Cosmonauts: Inside the Yuri Gagarin Training Center. Birkhäuser. ISBN 978-0-387-21894-6.</ref>

<ref name=Stanley_2016>Stanley, S. M. (2016). "Estimates of the magnitudes of major marine mass extinctions in earth history". Proceedings of the National Academy of Sciences of the United States of America. 113 (42): E6325–E6334. Bibcode:2016PNAS..113E6325S. doi:10.1073/pnas.1613094113. PMC 5081622. PMID 27698119. S2CID 23599425.</ref>

<ref name=stern2005>Stern, David P. (8 July 2005). "Exploration of the Earth's Magnetosphere". NASA. Archived from the original on 14 February 2013. Retrieved 21 March 2007.</ref>

<ref name="sun_future">Sackmann, I.-J.; Boothroyd, A. I.; Kraemer, K. E. (1993). "Our Sun. III. Present and Future". Astrophysical Journal. 418: 457–468. Bibcode:1993ApJ...418..457S. doi:10.1086/173407.</ref>

<ref name="sun_future_schroder">Schröder, K.-P.; Connon Smith, Robert (2008). "Distant future of the Sun and Earth revisited". Monthly Notices of the Royal Astronomical Society. 386 (1): 155–163. arXiv:0801.4031. Bibcode:2008MNRAS.386..155S. doi:10.1111/j.1365-2966.2008.13022.x. S2CID 10073988.
See also Palmer, Jason (22 February 2008). "Hope dims that Earth will survive Sun's death". NewScientist.com news service. Archived from the original on 15 April 2012. Retrieved 24 March 2008.</ref>

<ref name=tanimoto_ahrens1995>Tanimoto, Toshiro (1995). "Crustal Structure of the Earth" (PDF). In Thomas J. Ahrens (ed.). Global Earth Physics: A Handbook of Physical Constants. AGU Reference Shelf. Vol. 1. Washington, DC: American Geophysical Union. Bibcode:1995geph.conf.....A. doi:10.1029/RF001. ISBN 978-0-87590-851-9. Archived from the original (PDF) on 16 October 2006. Retrieved 3 February 2007.</ref>

<ref name=tp322_19>De Smet, J.; Van Den Berg, A.P.; Vlaar, N.J. (2000). "Early formation and long-term stability of continents resulting from decompression melting in a convecting mantle" (PDF). Tectonophysics. 322 (1–2): 19–33. Bibcode:2000Tectp.322...19D. doi:10.1016/S0040-1951(00)00055-X. hdl:1874/1653.</ref>

<ref name="T&S 137">Turcotte, D. L.; Schubert, G. (2002). "4". Geodynamics (2 ed.). Cambridge, England: Cambridge University Press. p. 137. ISBN 978-0-521-66624-4.</ref>

<ref name=ucs>"UCS Satellite Database". Nuclear Weapons & Global Security. Union of Concerned Scientists. 1 September 2021. Retrieved 12 January 2022.</ref>

<ref name=usno>"Selected Astronomical Constants, 2011". The Astronomical Almanac. Archived from the original on 26 August 2013. Retrieved 25 February 2011.</ref>

<ref name=USNO_TSD>"Leap seconds". Time Service Department, USNO. Archived from the original on 12 March 2015. Retrieved 23 September 2008.</ref>

<ref name=vazquez_etal2006>Vázquez, M.; Rodríguez, P. Montañés; Palle, E. (2006). "The Earth as an Object of Astrophysical Interest in the Search for Extrasolar Planets" (PDF). Lecture Notes and Essays in Astrophysics. 2: 49. Bibcode:2006LNEA....2...49V. Archived from the original (PDF) on 17 August 2011. Retrieved 21 March 2007.</ref>

<ref name=VSOP87>Simon, J.L.; et al. (February 1994). "Numerical expressions for precession formulae and mean elements for the Moon and planets". Astronomy and Astrophysics. 282 (2): 663–683. Bibcode:1994A&A...282..663S.</ref>

<ref name=ward_brownlee2002>Ward, Peter D.; Brownlee, Donald (2002). The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World. New York: Times Books, Henry Holt and Company. ISBN 978-0-8050-6781-1.</ref>

<ref name="watersource">Morbidelli, A.; et al. (2000). "Source regions and time scales for the delivery of water to Earth". Meteoritics & Planetary Science. 35 (6): 1309–1320. Bibcode:2000M&PS...35.1309M. doi:10.1111/j.1945-5100.2000.tb01518.x.</ref>

<ref name="WGS-84-2">Humerfelt, Sigurd (26 October 2010). "How WGS 84 defines Earth". Home Online. Archived from the original on 24 April 2011. Retrieved 29 April 2011.</ref>

<ref name="Williams1994">Williams, James G. (1994). "Contributions to the Earth's obliquity rate, precession, and nutation". The Astronomical Journal. 108: 711. Bibcode:1994AJ....108..711W. doi:10.1086/117108. ISSN 0004-6256. S2CID 122370108.</ref>

<ref name=williams_santosh2004>Rogers, John James William; Santosh, M. (2004). Continents and Supercontinents. Oxford University Press US. p. 48. ISBN 978-0-19-516589-0.</ref>

<ref name=zeilik1998>Zeilik, Michael; Gregory, Stephen A. (1998). Introductory Astronomy & Astrophysics (4th ed.). Saunders College Publishing. p. 56. ISBN 978-0-03-006228-5.</ref>

<ref name=earthmass>"Planetary Physical Parameters". Jet Propulsion Laboratory. 2008. Retrieved 11 August 2022.</ref>

<ref name=Narottam2008>Gaan, Narottam (2008). Climate Change and International Politics. Kalpaz Publications. p. 40. ISBN 978-81-7835-641-9.</ref></references>

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