1. Crust: The thin, rocky outer layer of the Earth. It's divided into oceanic crust (thinner and denser) and continental crust (thicker and less dense).

2. Mantle: The thickest layer, made up of hot, dense rock. It's mostly solid, but behaves like a very viscous fluid over long periods.

3. Outer Core: A liquid layer of iron and nickel. The movement of this layer is what generates Earth's magnetic field.

4. Inner Core: A solid ball of iron and nickel at the center of the Earth. The immense pressure from all the layers above is so great that it keeps the core solid despite extremely high temperatures.