Earth, the largest rocky planet, was formed about 4.5 billion years ago. The Earth's interior is divided into four layers which is typical of rocky planets. It is cool on the surface but very hot deep inside the planet. The center, or core, is as hot as 9000 degrees F.
The Earth's surface is unique from the other planets because it is the only one with liquid water. Water helps to make surface features such as rivers, lakes and oceans. The moving plates of the Earthís surface form other surface features such as mountains, earthquakes and volcanoes.