Beyond the outer core lies the mantle, a 1,800-mile-thick layer of viscous molten rock on which Earth's outermost layer, the crust, rests. On land, the continental crust is an average of 19 miles ...

This thermal energy is contained in the rock and fluids beneath Earth’s crust. It can be found from shallow ground to several miles below the surface, and even farther down to the extremely hot ...