Diagram showing the interior of the planet Earth. The outermost layer is the crust. Its depths varies greatly, from about 5 miles (8 km) under the oceans, to about five times this under the continents. Underneath the crust is the thick mantle, down to a depth of about 1800 miles (2900 km). It is a solid but pliable shell of olivine - a compound made from iron, magnesium, oxygen and silicon. Lastly there is the two-part core: a liquid outer core (yellow) and a solid inner core (white). Both parts are made of nickel-iron.