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

2. Mantle: The thickest layer of the Earth, located beneath the crust. It's mostly solid but can behave like a very viscous fluid over long periods. The mantle is responsible for plate tectonics.

3. Outer Core: A liquid layer composed primarily of iron and nickel. It's responsible for generating the Earth's magnetic field.

4. Inner Core: A solid sphere of iron and nickel at the Earth's center. It's extremely hot and under immense pressure.