Earth's interior is characterized by gradual increases in temperature, pressure and density. Heat continually flows outward into space. The temperature and pressure greatly affect the mechanical behavior or strength of earth materials. Plate tectonics - a recent theory in the Geological Sciences describing the dynamic processes. Plates move relative to one another as they slide over the asthenosphere through a combination of gravitational forces and thermal convection in the mantle.
Plates form from molten rock which wells up to the earth's surface at divergent plate boundaries .
Plates are either consumed where one slides beneath another, or form mountain belts where one collides with another at convergent plate boundaries . Regions where oceanic lithosphere is being consumed are called subduction zones . Plates slide past one another at transform plate boundaries . The Rock Cycle - describes many of the interrelationships observed in geology.