crust

The outer layer of the Earth, which varies in thickness between 6 and 48 kilometres, and floats on and surrounds the mantle. It comprises oceanic crust and continental crust, and the thick continental crust and much thinner oceanic crust are separated from the mantle below by the Mohorovicic discontinuity. The crust is made largely of oxygen (47%) and silicon (28%), with much smaller amounts of aluminium (8%), iron (5%), calcium (4%), sodium (3%), potassium (3%), and magnesium (2%). It is effectively the Earth's outer skin, occupying much less than 1% of the volume of the planet. All of the Earth's landforms (mountains, plains, and plateaux) are contained within it, along with the oceans and seas. Whilst the crust appears to be solid, it is subject to repeated movement (including bending, folding, and breaking) associated with the movement of material on the mantle below.