The Earth is made up of four main layers: the crust, the mantle, the outer core, and the inner core. The crust is the thin, solid outer layer where we live. Beneath it lies the mantle, a thick layer of hot, semi-solid rock that flows slowly over time. Below the mantle, the outer core is a liquid layer composed mainly of iron and nickel. It generates the Earth's magnetic field. At the center is the inner core, a solid sphere made of iron and nickel, with temperatures as high as 5,700 degrees Celsius (10,300 degrees Fahrenheit).