Plate Boundaries It is apparent that most of what we observe on the surface of the earth and at shallow depth is related in some way to plate tectonics. The beaches along the eastern margin of North America are the result of the weathering, erosion, and breakdown of a huge mountain range (the Appalachian Mountains) over the last 300 million years. The Appalachians were formed during the collision of continents to form a mega continent called Pangaea. The volcanic mountains that form the western margin of North America are the result of subduction of oceanic crust under continental crust. The subduction results is frictional heating and partial melting of material being dragged down into the mantle.
The plates move very slowly but constantly, and this moment is called tectonics; thus the theory of moving lithospheric plates is what you called PLATE TECTONICS