The theory concerning the structure of the earth and the processes occurring which explain the configuration of the continents and the location of earthquakes and volcanic activity. There are three types of plate margins, or boundaries between plates, depending on the two types of crusts that are interacting: oceanic with oceanic, continental with continental, or continental with oceanic. The rift valleys of the atlantic are an example of an oceanic margin where divergence has occurred, while oceanic convergence is illustrated by a striking example in the pacific. There, subduction of the philippine plate by the pacific plate has created the mariana trench, which at 36,198 ft. (10,911 m) is the deepest depression on earth.