The Earth is the third, and largest, of the terrestrial planets of the inner Solar System. It is only in the last few hundred years, however, that we have come to think of the Earth as just another planet, like the ones we see in the sky. Earth is very special because it is the only planet we know of that has the right concentrations and abundances of chemicals that support life. Surface Earth is composed mainly of rock but its surface is quite varied. The main features visible from space are the deep, blue oceans of salty water, surrounding the green and brown land masses.
Water covers two thirds of the planet's surface.
On the continents, some parts are covered with sandy soil and some are covered with vegetation. They also have networks of rivers and streams. At the polar regions the Earth has white ice caps whose size varies with the seasons. The surface of the Earth is geologically very active. It is broken up into large crustal plates, which move slowly and push against each other, forming mountains and causing earthquakes.