Sedimentary rocks may be found anywhere on Earth. When sedimentary rocks are heated and squeezed, they become metamorphic rocks. Igneous rocks have a volcanic origin. Over a very long time, rocks get recycled, in two ways. When marine sediments are raised above sea level, they get weathered, and the pieces carried down to the sea. On a much longer time-scale continental plates may collide. Then one plate goes under the other (is subducted), and all its material is recycled, emerging much later.