Earth

Third planet from the Sun. It is almost spherical, flattened slightly at the poles, and is composed of five concentric layers: inner core, outer core, mantle, crust, and atmosphere. About 70% of the surface (including the north and south polar ice caps) is covered with water. The Earth is surrounded by a life-supporting atmosphere and is the only planet on which life is known to exist.

Mean distance from the Sun
149,500,000 km/92,860,000 mi

Equatorial diameter
12,755 km/7,920 mi

Circumference
40,070 km/24,900 mi

Rotation period
23 hours 56 minutes 4.1 seconds

Year
(complete orbit, or sidereal period) 365 days 5 hours 48 minutes 46 seconds. The Earth's average speed around the Sun is 30 kps/18.5 mps. The plane of its orbit is inclined to its equatorial plane at an angle of 23.5°; this is the reason for the changing seasons

Atmosphere
nitrogen 78.09%; oxygen 20.95%; argon 0.93%; carbon dioxide 0.03%; and less than 0.0001% neon, helium, krypton, hydrogen, xenon, ozone, and radon

Surface
land surface 150,000,000 sq km/57,500,000 sq mi (greatest height above sea level 8,872 m/29,118 ft Mount Everest); water surface 361,000,000 sq km/139,400,000 sq mi (greatest depth 11,034 m/36,201 ft Mariana Trench in the Pacific). The interior is thought to be an inner core about 2,600 km/1,600 mi in diameter, of solid iron and nickel; an outer core about 2,250 km/1,400 mi thick, of molten iron and nickel; and a mantle of mostly solid rock about 2,900 km/1,800 mi thick. The crust and the uppermost layer of the mantle form about twelve major moving plates, some of which carry the continents. The plates are in constant, slow motion, called tectonic drift

Satellite
the Moon

Age
4.6 billion years. The Earth was formed with the rest of the Solar System by consolidation of interstellar dust. Life began 3.5–4 billion years ago.