The thin crust of the Earth, like the shell of an egg, is all that protects the surface and continents from the hot molten rock inside. Deep inside the Earth at the center is the core. Between the surface of the Earth and the core is the mantle. It is the continents, or rather tectonic plates underneath the Earth's surface that move on top of this mantle. These eight major tectonic plates are 100~200 km thick and create the Earth's crust. The movement of continents relative to each other is referred to as continental drift. Understanding how and why this is happening has important consequences for everyday lives.