Structure of the Earth. Cutaway computer illustration showing the internal structure of the Earth. From the centre outwards, the five layers shown are: inner and outer core (yellow), inner and outer mantle (orange and red), and crust. The core is around 15% of the volume of the Earth, and the mantle is around 80%. The crust is a thin (5-70 kilometres thick) rock layer over the 12,756-kilometre-diameter Earth. The core is heavy iron and nickel metal that sank to Earth's centre. The inner core is solid, but the liquid outer core generates the Earth's magnetic field. The mantle is molten rock, and the inner mantle is more fluid than the outer mantle due to higher temperatures, which exceed 6000 degrees Celsius in the core.