Earth is the fifth largest planet in the solar system, third in order of distance from the Sun. It is the largest of its planetary system's terrestrial planets and the only place in the universe known to support life.
The most prominent features of the earth's climate are its two large polar regions, two relatively narrow temperate zones, and a wide equatorial tropical to subtropical region. Precipitation patterns vary widely according to location, ranging from several meters of water per year to less than a millimeter. About 70 percent of the surface is covered by salt-water oceans. The remainder consists of continents and islands, with the vast majority of the inhabited land in the Northern Hemisphere.
Earth has evolved through geological and biological processes that have left traces of the original conditions. The outer surface is divided into several tectonic plates that gradually migrate across the surface over geologic time spans, which at least several times have changed relatively quickly. The interior of the planet remains active, with a thick layer of molten Earth mantle and an iron-filled core that generates a magnetic field