Famous "Blue Marble" photograph of Earth, taken from Apollo 17. Orbital characteristics Epoch J2000 Aphelion 152,097,701 km 1.0167103335 AU Perihelion 147,098,074 km 0.9832898912 AU Semi-major axis 149,597,887.5 km 1.0000001124 AU Eccentricity 0.016710219 Orbital period 365.256366 days 1.0000175 yr Average orbital speed 29.783 km/s 107,218 km/h Inclination Reference (0) 7.25° to Sun's equator Longitude of ascending node 348.73936° Argument of perihelion 114.20783° Satellites 1 (the Moon) Physical characteristics Mean radius 6,371.0 km[1] Equatorial radius 6,378.1 km[2] Polar radius 6,356.8 km[2] Flattening 0.0033528[2] Circumference 40,075.02 km (equatorial) 40,007.86 km (meridional) 40,041.47 km (mean) Surface area 510,072,000 km²[3] 148,940,000 km² land  (29.2 %) 361,132,000 km² water (70.8 %) Volume 1.0832073×1012 km³ Mass 5.9736×1024 kg Mean density 5.5153 g/cm³ Equatorial surface gravity 9.780327 m/s²[4] 0.99732 g Escape velocity 11.186 km/s  40,270 km/h Sidereal rotation period 0.997258 d 23h 56m 04.09054s[4] Equatorial rotation velocity 465.11 m/s Axial tilt 23.439281° Albedo 0.367 Surface temp.    Kelvin    Celsius min mean max 184 K 287 K 331 K -89 °C 14 °C 57.7 °C Adjectives Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure 101.3 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)[5] Earth (pronounced /'???/)[6] is the third planet from the Sun and is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the Earth, Planet Earth, the World, and Terra.[7] Home to millions of species,[8] including humans, Earth is the only place in the universe where life is known to exist. Scientific evidence indicates that the planet formed 4.54 billion years ago,[9][10][11][12] and life appeared on its surface within a billion years. Since then, 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 radiation, permitting life on land.[13] Earth's outer surface is divided into several rigid segments, or tectonic plates, that gradually migrate across the surface over periods of many millions of years. About 71% of the surface is covered with salt-water oceans, the remainder consisting of continents and islands; liquid water, necessary for all known life, is not known to exist on any other planet's surface.[14][15] Earth'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 outer space, including the Sun and the Moon. At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis. This length of time is a sidereal year, which is equal to 365.26 solar days.[16] The Earth's axis of rotation is tilted 23.4° away from the perpendicular to its orbital plane,[17] 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. A cometary bombardment during the early history of the planet played a role in the formation of the oceans.[18] Later, asteroid impacts caused significant changes to the surface environment.