Plate Tectonics

Most geologists believe convective cells in the earth's interior are the driving force for plate motion. If you have ever seen a rapidly boiling pot of water, then you know about convection cells. In the center of the pot, bubbles rise to the surface and push water to the sides. Along the sides, the water cools and descends back down to the bottom of the pot to be heated again.

In a similar way, convection cells in the mantle bring molten rock to the surface along MORs where it forms new ocean crust. Below the crust, pressure is exerted on the bottom of the plates by the convection cell, helping to push the plates along, and causing divergence. At the trenches, the cells may also exert a downward force on the descending plates, helping to pull them down into the mantle.