1. Crust: This is the outermost layer, the thin, solid, and rocky shell we live on. It is relatively brittle and divided into oceanic crust (thinner and denser) and continental crust (thicker and less dense).

2. Mantle: This is the thickest layer, extending from the crust to the core. It is mostly solid, but behaves like a very viscous fluid over geological time. The mantle is responsible for plate tectonics and volcanic activity.

3. Core: This is the Earth's innermost layer, composed of a solid inner core and a liquid outer core. The core is primarily composed of iron and nickel, and its extreme heat generates Earth's magnetic field.