Computer illustration showing Earth's internal structure. The core consists of an inner region and an outer region. The mantle consists of the mesosphere, the athenosphere, and the lower part of the lithosphere. The crust is the upper part of the lithosphere. The crust is around 40 kilometres thick in the continents, and as little as 5 kilometres thick in the deep ocean. The mantle is a viscous layer of rock some 2900 kilometres deep. The outer core is a liquid composed of molten iron and nickel. Convection currents in these metals are responsible for producing the Earth's magnetic field. The outer core is around 2250 kilometres thick. Below it is the solid inner core which is a hot, solid sphere of iron and nickel, some 1200 kilometres in radius, at a temperature of around 5500 degrees Celsius.