Think of Earth as a giant ball with a core at its center and a mantle around that. Both layers of rock are extremely hot—hot enough to keep the rock in a liquid state.
The outermost layer of Earth is called the crust, and it’s made up of several enormous slabs, called tectonic plates. The plates fit together like a giant jigsaw puzzle, but they are constantly moving—a few inches every year. As the plates move, mountains are formed.