1. Crust: This is the outermost layer, the one we live on. It's relatively thin, ranging from 3-5 miles thick under the oceans (oceanic crust) to 25 miles thick under the continents (continental crust). It's mostly composed of rocks like granite and basalt.

2. Mantle: This is the thickest layer, extending about 1800 miles down. It's mostly solid rock, but it's incredibly hot and can flow very slowly over long periods. This flow drives the movement of tectonic plates.

3. Outer Core: This layer is about 1400 miles thick and is composed mostly of liquid iron and nickel. It's incredibly hot, and the movement of this liquid metal generates Earth's magnetic field.

4. Inner Core: This is the Earth's center, a solid ball of mostly iron and nickel. It's incredibly hot, even hotter than the outer core, but the immense pressure keeps it from melting.

Let me know if you'd like to learn more about any of these layers!