Earth's internal structure. Cutaway artwork showing the different layers that make up the structure of the Earth. The external layer (crust) shows the Earth's surface topography and atmosphere, including land, water and clouds. The crust extends downwards for around 35 kilometres. The mantle is divided into the external mantle (light orange), composed of solid rock (600 kilometres) and the internal mantle, composed of semi-molten rock (dark orange, 2300 kilometres). The outer core (orange) is a liquid layer of iron and nickel, around 2160 kilometres thick. The inner core (centre) is a liquid sphere of iron-nickel alloy, with a radius of 1320 kilometres.