Earth's structure. Diagram of the internal structure of the Earth. Below the Earth's crust, a zone of near-molten rock called the mantle extends down to 2885 kilometres (km). The Mantle consists of three layers: the lithosphere, the asthenosphere, and the mesosphere. Beneath the mantle is the nickel-iron outer core. It is about 7000 km across. The outer core (orange) is molten and the inner core (red) is solid. The temperature at the core may be over 5000 degrees Celsius.