Earth is made up of four main layers: the crust, mantle, outer core, and inner core. The crust is the thin, solid outer layer where we live. Below it lies the mantle, a thick layer of hot, semi-solid rock that flows slowly over time. Beneath the mantle is the outer core, which is liquid and composed mainly of iron and nickel. The innermost layer, the inner core, is solid and extremely hot, also made primarily of iron. Together, these layers play a crucial role in Earth's geology and magnetic field.