The theory of plate tectonics emerged as the great unifying model of earth dynamics in the latter third of the 20th Century. An indication of the lithosphere s segmented nature is the world-wide pattern of earthquakes. As seen in this seismisity map , the earthquakes are not randomly distributed. Rather, they cluster together along lines. Compare this map to the map of known plate boundaries .
Plates can move over the molten rock of the asthenosphere.
Interactions between plates occur along plate boundaries. Plates can move apart, come together, or slide past each other. The key to understanding plate tectonics is understanding the types of boundaries and what happens at each. Plates move apart. Rising hot rock pushes crust upwards.