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Earth   "The Blue Marble" photograph of Earth, taken from Apollo 17 Alternate name(s) Terra Epoch J2000.0 Aphelion 152,098,232 km 1.01671388 AU Perihelion 147,098,290 km 0.98329134 AU Semi-major axis 149,598,261 km 1.00000261 AU Eccentricity 0.01671123 Orbital period 365.256363004 days 1.000017421 yr Average orbital speed 29.78 km/s 107,200 km/h Mean anomaly 357.51716° Inclination 7.155° to Sun's equator 1.57869° to invariable plane Longitude of ascending node 348.73936° Argument of perihelion 114.20783° Satellites 1 natural (The Moon) 8,300+ artificial (as of 1 March 2001 (2001 -03-01)) Mean radius 6,371.0 km Equatorial radius 6,378.1 km Polar radius 6,356.8 km Flattening 0.0033528 Circumference 40,075.017 km (equatorial) 40,007.86 km (meridional) Surface area 510,072,000 km2148,940,000 km2 land (29.2 %) 361,132,000 km2 water (70.8 %) Volume 1.08321×1012 km3 Mass 5.9736×1024 kg Mean density 5.515 g/cm3 Equatorial surface gravity 9.780327 m/s2 0.99732 g Escape velocity 11.186 km/s Sidereal rotation period 0.99726968 d 23h 56m 4.100s Equatorial rotation velocity 1,674.4 km/h (465.1 m/s) Axial tilt 23°26'21".4119 Albedo 0.367 (geometric) 0.306 (Bond) Surface temp.    Kelvin    Celsius min mean max 184 K 287.2 K 331 K -89.2 °C 14 °C 57.8 °C Surface pressure 101.325 kPa (MSL) Composition 78.08% nitrogen (N2) 20.95% oxygen (O2) 0.93% argon 0.038% carbon dioxide About 1% water vapor (varies with climate) Earth (or the Earth) is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet, or by its Latin name, Terra.Earth formed 4.54 billion years ago, and life appeared on its surface within one billion years. The planet is home to millions of species, including humans. Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land. The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist during this period. The planet is expected to continue supporting life for at least another 500 million years.Earth's outer surface is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the hydrosphere. Earth's poles are mostly covered with solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap). The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.Earth interacts with other objects in space, especially the Sun and the Moon. At present, Earth orbits the Sun once every 366.26 times it rotates about its own axis, which is equal to 365.26 solar days, or one sidereal year. The Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt, and gradually slows the planet's rotation. Between approximately 3.8 billion and 4.1 billion years ago, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment.Both the mineral resources of the planet, as well as the products of the biosphere, contribute resources that are used to support a global human population. These inhabitants are grouped into about 200 independent sovereign states, which interact through diplomacy, travel, trade, and military action. Human cultures have developed many views of the planet, including personification as a deity, a belief in a flat Earth or in the Earth as the center of the universe, and a modern perspective of the world as an integrated environment that requires stewardship. Cite error: There are tags on this page, but the references will not show without a {{Reflist|group=note}} template or a tag; see the help page. Cite error: There are tags on this page, but the references will not show without a {{Reflist}} template or a tag; see the help page.
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