The crust of the Earth is made up of plates with different kinds of margins. In mid-ocean, there are constructive plate margins, where magma wells up from the Earth's interior, forming new crust. On continent–continent margins, mountain ranges are flung up by the collision of two continents. At an ocean–continent destructive margin, ocean crust is forced under the denser continental crust, forming an area of volcanic instability.

Inside the Earth. The surface of the Earth is a thin crust about 6 km/4 mi thick under the sea and 40 km/25 mi thick under the continents. Under the crust lies the mantle, about 2,900 km/1,800 mi thick and with a temperature of 1,500–3,000°C/2,700–5,400°F. The outer core is about 2,250 km/1,400 mi thick, of molten iron and nickel. The inner core is probably solid iron and nickel, at about 5,000°C/9,000°F.

The Earth photographed by the Apollo 17 spacecraft in December 1972. This photograph extends from the Mediterranean to the Antarctic ice cap. Almost the entire coastline of Africa is visible and the Arabian Peninsula can be seen off the northeast edge of Africa. Asia is on the horizon to the northeast.

The Earth photographed by the crew of Apollo 17 on their way to the Moon. It was the first Apollo lunar trajectory that allowed photography of the south pole. Much of Africa and the Mediterranean are cloud-free, whereas large swathes of cloud dominate the southern Atlantic and Indian oceans.

The Earth rising above the Moon's horizon, as seen from the Apollo 11 spacecraft in July 1969.

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.

earth

Electrical connection between an appliance and the ground. In the event of a fault in an electrical appliance, for example, involving connection between the live part of the circuit and the outer casing, the current flows to earth, causing no harm to the user.
In most domestic installations, an earth is created by a connection to a metal water-supply pipe buried in the ground

Source  :  http://encyclopedia.farlex.com/