The Lithosphere of the Earth
The layer under the Earth's crust is called the lithosphere. The lithosphere and crust seem to be separate from the rest of the Earth's interior, and float on top of the warmer interior layers of the Earth the way a rubber tire can float on the surface of a swimming pool. The lithosphere and crust together comprise the surface of the Earth.
Underneath the surface, the Earth just keeps getting hotter and hotter.