It's the outermost layer, and the one we live on. It's relatively thin compared to the other layers, ranging from about 3-5 miles (5-8 km) thick under the oceans to 25 miles (40 km) thick under the continents.

There are two types of crust:

* Oceanic crust: Thinner and denser, made mostly of basalt.

* Continental crust: Thicker and less dense, made mostly of granite.