Earth
the Earth the only planet that has an atmosphere containing 21 percent oxygen. It is the only planet that has liquid water on its surface, and It is the only planet in the solar system that has life. The Earth is the only inner planet (Mercury, Venus, earth and mars) to have one large satellite, the moon. Mars has two very tiny moons. Mercury and Venus have none. The Earth is fragile. Its surface is split into plates (tectonic plates) which float on a rocky mantle – the layer between the surface of the earth, its crust, and its hot liquid core. The inside of the Earth is active and Earthquakes, volcanoes and mountain building takes place along the boundaries of the tectonic plates.