2 (g.d.a.)  How Plates move

The theory of plate tectonics (tek tahn iks) states that pieces of Earth’s lithosphere are in slow, constant motion, driven by convection currents in the mantle.  Geologists think that movement of convection currents in the mantle is the major force that causes plate motion. During subduction, gravity pulls one edge of a plate down into the mantle. The rest of the plate also moves. These changes include volcanoes, mountain ranges, and deep-ocean trenches.