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 approximately 4.54 billion years ago by accretion from the solar nebula, 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 biotic 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. The planet is expected to continue supporting life for another 500 million to 2.3 billion years.
Earth's crust 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 onesidereal 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 billionyears 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 and 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 (193 United Nations recognized 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.
Designations
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| Alternate name(s) | Terra | |||||||||
Orbital characteristics
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| 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) 994 artificial (as of 31 December 2011) | |||||||||
Physical characteristics
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| Mean radius | 6,371.0 km | |||||||||
| Equatorialradius | 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 km2
148,940,000 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 |
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Atmosphere
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| 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) | |||||||||
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