1. Crust: This is the outermost layer, the one we live on. It's relatively thin, ranging from about 3-5 miles (5-8 km) thick under the oceans (oceanic crust) to around 25 miles (40 km) thick under the continents (continental crust).

2. Mantle: This is the thickest layer, extending about 1800 miles (2900 km) below the crust. It's primarily made of solid rock but can behave like a very viscous fluid over long periods due to immense heat and pressure.

3. Outer Core: This layer is about 1400 miles (2200 km) thick and is made mostly of liquid iron and nickel. The movement of the outer core creates Earth's magnetic field.

4. Inner Core: The innermost layer, about 750 miles (1220 km) thick, is mostly solid iron and nickel. Despite the immense pressure and heat, it remains solid due to the extreme pressure.