Earth's structure. Illustration of a section of the Earth, showing its internal structure. Below the Earth's crust, a zone of near-molten rock called the mantle extends down to 2890 kilometres (km). Beneath the mantle is the nickel-iron outer core, which is about 7000 km across. The outer core is molten and the inner core (red) is solid. The internal pressures at different depths are shown in gigapascals (GPa). The temperature at the core may be over 5000 degrees Celsius.