Red Space Rocket

The earth is not just a large ball of identical rock. Beneath our feet are a number of different layers and they behave differently. Once big difference between the surface and the layers below in that inside the earth high pressures and high temperatures are what is normal.

Here is a link to a lot more information to explain how this all works.

Structure of the Earth – Wikipedia, the free encyclopedia

The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core.