Here's why:

* Continental crust is the layer that makes up the continents. It's primarily composed of granitic rocks and is generally thicker than oceanic crust, ranging from 30-70 kilometers (19-43 miles) thick.

* Oceanic crust makes up the ocean floor and is primarily composed of basaltic rocks. It's thinner than continental crust, averaging about 7 kilometers (4 miles) thick.

Let me know if you have any other questions about the Earth's structure!