The theory of plate tectonics, formerly known as continental drift, is a working model that describes the movement of the continents and sea floor across the surface of the Earth. The theory explains many anomalous facts about Earth's geology, such as the present arrangement of landmasses.
Plate tectonics is the underlying theory of modern geology. It explains many discoveries that cannot be understood outside of the context of an active crust. The theory's model of action proposes that the entire crust of the Earth is broken into large plates. These plates grind against each other at their margins as subterranean currents push them around the surface. In some places, dense sea floor slides under the lighter, more buoyant continental rock, while in other places the sea floor is spreading, which creates new crust.
This theory explains the massive mid-ocean ridge formations as zones of sea floor spread, and the so-called ring of fire around the Pacific Ocean as the result of subduction in the sea floor. The theory also provides a ready explanation for the jigsaw shape of the continents, as well as providing an understanding of how some mineral deposits can run out to the edge of the continental shelf, stop at the ocean and start back up again on a different continent thousands of miles away.