Earth [%PREMIUM_LINK%] (ûrth) Pronunciation Key |
The third planet from the Sun and the densest planet in the solar system. Earth is a terrestrial or inner planet consisting of a thin outer crust, an intermediate mantle, and a dense inner core. It has an atmosphere composed primarily of nitrogen and oxygen and is the only planet on which water in liquid form exists, covering more than 70 percent of its surface. It is also the only planet on which life is known to have evolved, occupying the relatively thin region of water, land, and air known as the biosphere. Earth has a single, relatively large natural satellite, the Moon. See more at atmosphere, core, crust, mantle. See Table at solar system.
Electricity See ground.