ools down when exposed to the cooled environment outside; the layer of cooled magma forms the lithosphere. When magma flows out from the ridges, the crust is fractured and a new ocean floor is built spreading perpendicularly away from the ridge. Because of this constant upwelling, the ocean is relatively shallow in these areas. Sea floor spreading and continental drift are the products of this continual upwelling. The cooled magma will, in time, sink back down into the Earth in the deep ocean trenches. The mantle sinking down produces subduction zones. The deepest part of the ocean resides in these areas. There are three types of boundaries where plates meet: divergent boundaries -- the upwelling of magma; convergent boundaries where the plates collide producing mountains, volcanoes, and earthquakes; and transform boundaries -- lateral m!
             ovement. Transform plates are caused by fracture zones. When a rift opens from the upwelling of magma it causes a crack in the crust. As new magma rises to the surface, the crack increases caused by the pressure, resulting in a horizontal faulting. The fractured plate pieces travel in the same direction as the original plate was traveling -- away from the ocean ridge.
             During the early 1900's, a theory of a 'super-continent' was developed by Alfred Wegener. He was ridiculed for his ideas that continental drift produced the present positions of the continents from a single 'super-continent' called Pangea. This theory is widely accepted today, however. There was abundant evidence for Wegener to believe in the existance of Pangea. The shape of the continents could be pieced together like a giant jigsaw puzzle suggesting that the continents were once 'glued' together. The fossils found on the continents were not distinct to that particular land, but were also found in lands that were separated by thousands of kilometers of water. Fossils indicated that identical species existed in different continents. ...