Earth

Earth is the third planet from the Sun in the Solar System. It is the only planet known to have life on it.

Earth

The Blue Marble, the first full-view photograph of the planet taken by Apollo 17 astronauts in 1972
Designations
Adjectives	Earthly, terrestrial, terran, tellurian
Orbital characteristics
Epoch J2000[1]
Aphelion	152100000 km[2] (94500000 mi; 1.017 AU)
Perihelion	147095000 km[2] (91401000 mi; 0.98327 AU)
Semi-major axis	149598023 km[3] (92955902 mi; 1.00000102 AU)
Eccentricity	0.0167086[3]
Orbital period	365.256363004 d[4] (1.00001742096 yr)
Average orbital speed	29.78 km/s[5] (107200 km/h; 66600 mph)
Mean anomaly	358.617°
Inclination	7.155° to the Sun's equator; 1.57869°[6] to invariable plane; 0.00005° to J2000 ecliptic
Longitude of ascending node	−11.26064°[5] to J2000 ecliptic
Argument of perihelion	114.20783°[5]
Satellites	1 natural satellite: the Moon 5 quasi-satellites >1 800 operational artificial satellites[7] >16 000 space debris[8]
Physical characteristics
Mean radius	6371.0 km (3958.8 mi)[9]
Equatorial radius	6378.1 km (3963.2 mi)[10][11]
Polar radius	6356.8 km (3949.9 mi)[12]
Flattening	0.0033528[13] 1/298.257222101 (ETRS89)
Circumference	40075.017 km equatorial (24901.461 mi)[11] 40007.86 km meridional (24859.73 mi)[14][15]
Surface area	510072000 km2 (196940000 sq mi)[16][17][18] 148940000 km2 land (57510000 sq mi; 29.2%) 361132000 km2 water (139434000 sq mi; 70.8%)
Volume	260 billion cubic miles [19]
Mass	5.97237×1024 kg (1.31668×1025 lb)[20] (3.0×10−6 M☉)
Mean density	5.514 g/cm3 (0.1992 lb/cu in)[5]
Surface gravity	9.807 m/s2 (1 g; 32.18 ft/s2)[21]
Moment of inertia factor	0.3307[22]
Escape velocity	11.186 km/s[5] (40270 km/h; 25020 mph)
Sidereal rotation period	0.99726968 d[23] (23h 56m 4.100s)
Equatorial rotation velocity	0.4651 km/s[24] (1674.4 km/h; 1040.4 mph)
Axial tilt	23.4392811°[4]
Albedo	0.367 geometric[5] 0.306 Bond[5]
Surface temp. min mean max Kelvin 184 K[25] 288 K[26] 330 K[27] Celsius −89.2 °C 14.9 °C 56.9 °C Fahrenheit −128.5 °F 58.7 °F 134.3 °F
Atmosphere
Surface pressure	101.325 kPa (at MSL)
Composition by volume	78.08% nitrogen (N 2; dry air)[5] 20.95% oxygen (O 2) 0.934% argon 0.0408% carbon dioxide[28] ~ 1% water vapor (climate variable)

The Earth formed about 4.6 billion years ago.^[29][30]

It is one of four rocky planets on the inner side of the Solar System. The other three are Mercury, Venus, and Mars.

The large mass of the Sun keeps the Earth in orbit through the force of gravity.^[31] Earth also turns around in space, so that different parts face the Sun at different times. Earth goes around the Sun once (one year) for every 365​¹⁄₄ times it turns around (one day).

Earth is the only planet in the Solar System that has a large amount of liquid water on its surface.^[32][33][34] About 71% of the surface of Earth is covered by liquid or frozen water.^[35] Because of this, people sometimes call it the blue planet.^[36]

Because of its water, Earth is home to millions of species of plants and animals which need water to survive.^[37][38] The things that live on Earth have changed its surface greatly. For example, early cyanobacteria changed the air and gave it oxygen. The living part of Earth's surface is called the "biosphere".^[39]

1. ↑ All astronomical quantities vary, both in time (secularly) and frequency (periodically). The quantities given are the values at the instant J2000.0 of the secular variation, ignoring all periodic variations.
2. ↑ ^{2.0 2.1} 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.
3. ↑ ^{3.0 3.1} Simon, J.L.; Bretagnon, P.; Chapront, J.; Chapront-Touzé, M.; Francou, G.; Laskar, J. (February 1994). "Numerical expressions for precession formulae and mean elements for the Moon and planets". Astronomy and Astrophysics. 282 (2): 663–83. Bibcode:1994A&A...282..663S.
4. ↑ ^{4.0 4.1} Cite error: The named reference IERS was used but no text was provided for refs named (see the help page).
5. ↑ ^{5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7} Williams, David R. (16 March 2017). "Earth Fact Sheet". NASA/Goddard Space Flight Center. Retrieved 26 July 2018.
6. ↑ Allen, Clabon Walter; Cox, Arthur N. (2000). Allen's Astrophysical Quantities. Springer. p. 294. ISBN 978-0-387-98746-0. Retrieved 13 March 2011.
7. ↑ "UCS Satellite Database". Nuclear Weapons & Global Security. Union of Concerned Scientists. 10 August 2018. Retrieved 27 September 2018.
8. ↑ 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.
9. ↑ Lide, David R. (2000). David R. Lide (ed.). Handbook of Chemistry and Physics (81st ed.). CRC. ISBN 978-0-8493-0481-1.
10. ↑ "Selected Astronomical Constants, 2011". The Astronomical Almanac. Archived from the original on 26 August 2013. Retrieved 25 February 2011.
11. ↑ ^{11.0 11.1} World Geodetic System (WGS-84). Available online Archived 2020-03-11 at the Wayback Machine from National Geospatial-Intelligence Agency.
12. ↑ 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.
13. ↑ 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). Dennis D. McCarthy, Gérard Petit, IERS Convertions Centre. Frankfurt am Main: Verlag des Bundesamts für Kartographie und Geodäsie. p. 12. ISBN 978-3-89888-884-4. Retrieved 29 April 2016.
14. ↑ Humerfelt, Sigurd (26 October 2010). "How WGS 84 defines Earth". Archived from the original on 24 April 2011. Retrieved 29 April 2011.
15. ↑ Earth's circumference is almost exactly 40,000 km because the metre was calibrated on this measurement—more specifically, 1/10-millionth of the distance between the poles and the equator.
16. ↑ Pidwirny, Michael (2 February 2006). "Surface area of our planet covered by oceans and continents.(Table 8o-1)". Fundamentals EBook. University of British Columbia, Okanagan. Retrieved 26 November 2007.
17. ↑ Staff (24 July 2008). "World". The World Factbook. Central Intelligence Agency. Archived from the original on 5 January 2010. Retrieved 5 August 2008.
18. ↑ 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 2015-03-26 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 shields of Antarctica and Greenland are counted as land, even though much of the rock that supports them lies below sea level.
19. ↑ "Earth's facts". factshungry. 10 May 2021. Archived from the original on 31 May 2021. Retrieved 24 May 2021.
20. ↑ Luzum, Brian; Capitaine, Nicole; Fienga, Agnès; Folkner, William; Fukushima, Toshio; et al. (August 2011). "The IAU 2009 system of astronomical constants: The report of the IAU working group on numerical standards for Fundamental Astronomy". Celestial Mechanics and Dynamical Astronomy. 110 (4): 293–304. Bibcode:2011CeMDA.110..293L. doi:10.1007/s10569-011-9352-4. ISSN 0923-2958. S2CID 122755461.
21. ↑ The international system of units (SI) (PDF) (2008 ed.). United States Department of Commerce, National Institute of Standards and Technology Special Publication 330. p. 52. Archived from the original (PDF) on 3 June 2016. Retrieved 13 June 2019.
22. ↑ 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.
23. ↑ Allen, Clabon Walter; Cox, Arthur N. (2000). Allen's Astrophysical Quantities. Springer. p. 296. ISBN 978-0-387-98746-0. Retrieved 17 August 2010.
24. ↑ 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.
25. ↑ "World: Lowest Temperature". WMO Weather and Climate Extremes Archive. Arizona State University. Archived from the original on 16 June 2010. Retrieved 7 August 2010.
26. ↑ Kinver, Mark (10 December 2009). "Global average temperature may hit record level in 2010". BBC. Retrieved 22 April 2010.
27. ↑ "World: Highest Temperature". WMO Weather and Climate Extremes Archive. Arizona State University. Archived from the original on 4 January 2013. Retrieved 7 August 2010.
28. ↑ "Trends in Atmospheric Carbon Dioxide: Recent Global CO
    2 Trend". Earth System Research Laboratory. National Oceanic and Atmospheric Administration. 26 July 2018. Archived from the original on 26 July 2018.
29. ↑ 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 28 July 2009.
30. ↑ Dalrymple G. Brent 2004. Ancient Earth, ancient skies: the age of Earth and its cosmic surroundings. Stanford. p26, table 3.1
31. ↑ See Formation and evolution of the Solar System for an account
32. ↑ name="Gomes">R. Gomes H.F.; et al. (2005). "Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets" (PDF). Nature. 435 (7041): 466–469. Bibcode:2005Natur.435..466G. doi:10.1038/nature03676. PMID 15917802. S2CID 4398337.
33. ↑ A. Morbidelli J.; et al. (2000). "Source regions and timescales for the delivery of water to the Earth". Meteoritics & Planetary Science. 35 (6): 1309–1320. Bibcode:2000M&PS...35.1309M. doi:10.1111/j.1945-5100.2000.tb01518.x. ISSN 1086-9379. S2CID 129817341.
34. ↑ "Rover reveals Mars was once wet enough for life". Microsoft. Archived from the original on 10 February 2004. Retrieved 28 July 2009.
35. ↑ The source of the water is not known for sure, but we do know water is in some meteorites. "Winchcombe meteorite bolsters Earth water theory" [1]
36. ↑ Blue Planet is a poetic title for the Earth used in movies, in cheap paper books, in poetry, and in government reports (such as the European Space Agency's Exploring the water cycle of the Blue Planet)
37. ↑ May, Robert M. (1988). "How many species are there on Earth". Science. 241 (4872). Harvard University: 1441–1449. Bibcode:1988Sci...241.1441M. doi:10.1126/science.241.4872.1441. PMID 17790039. S2CID 34992724. Retrieved 28 July 2009.
38. ↑ Purves, William Kirkwood (2001). Life, the science of biology. Macmillan. p. 455. ISBN 978-0-7167-3873-2.
39. ↑ "Origins of life on Earth". Space.com. Archived from the original on 28 July 2009. Retrieved 28 July 2009.