Earth is round, like an orange. Oranges have a skin and Earth has a skin, too. We call this skin Earth’s crust. Under the crust, there is very hot rock.
Earth’s crust has different pieces. These pieces move very, very slowly. Millions of years ago, the pieces moved and made mountains. Under mountains, the crust is thick, but under the ocean, it’s thinner. When two pieces of the crust move and meet, there can be earthquakes.
A volcano is a hole in Earth’s crust. When a volcano erupts, hot rock flies out from under the ground, and melted rock pours out over the ground. Volcanoes under the ocean sometimes make new islands. In 1963, a volcano in the Atlantic Ocean made a new island called Surtsey.
There are many different rocks in Earth’s crust. They are millions of years old. The rocks are often different colors. In the Painted Desert in Arizona in the USA, you can see the different rocks.