About 250 million years ago, the entire land mass of the Earth formed a single super-continent called Pangaea which has since broken apart. Its pieces drifted away from one another to form the continents. In the Jurassic period Pangaea broke into two masses, Gondwana which formed Africa, India, Australia and South America, and Laurasia which included what is now North America, Asia, Europe, Iceland and Greenland.
Geologist Alfred Wegener proposed the theory of continental drift in 1915 and it became widely accepted among the geoscientific community in the 1960s when the concept of sea floor spreading was developed. According to the University of California Museum of Paleontology, at this time scientists found that mid-oceanic ridges were areas where new crust was forming by magma released as the sea floor spread and old crust submerged back into the Earth's core in deep ocean trenches. This movement also causes the movement of continental plates at a rate of between one-third of an inch and 4 inches annually.
Three types of tectonic boundaries are created by plate movement. Convergent boundaries occur when plates move into one another, crumpling the crust or forcing one plate to lift above another. This type of plate movement is what produced the Mariana Trench, the Andes and Himalayas. Divergent boundaries occur when two plates are pushed apart by magma from the mantle rising to the surface. A divergent plate boundary is also present in Africa's Great Rift Valley. When two plates grind past each other it is called a transform boundary or lateral slipping, an example of which is California's San Andreas Fault.
Earthquakes and volcanic activity are the result of tectonic movements. The breaking up of rocks inside continental plates causes earthquakes along the plates' fault lines where sufficient strain energy has built up. Earthquakes also occur along convergent and transform plate boundaries. Volcanoes appear where divergent plate boundaries form on continents as well as on convergent boundaries as a result of the melting of old crust.