Earth's core, mantle, and crust
Geology is the study of Earth. Geologists believe Earth is comprised of a core, mantle, and crust. If you imagine the sphere-shaped Earth were cut in half as you might cut a melon, it’s easy to visualize.
The core is at the center of the sphere. The inner part of the core is thought to be solid. The outer core is believed to be very hot – so hot that it is molten: When solid substances such as rock or metal become hot enough, they melt into a liquid.
The thick layer surrounding Earth’s core is the mantle. The mantle is probably cooler than the outer core, but it is still hot enough to be partially molten.
The thin, outer layer is the crust. We know about the crust because we live on it. Compared to the mantle and core, the crust is very cool and solid. The continental land masses and the ocean floor both form Earth’s crust.