In geology, a theory that explains the distribution of continents, earthquakes, volcanoes,, mountains and other geologic phenomena in terms of the formation, movement, and destruction of tectonic plates. These plates move in response to forces deep within the Earth. Because continents, such as North America, often ride piggy-back on plates, their movement is referred to as continental drift.
Note: Earthquakes and volcanoes tend to occur at the boundaries between plates: the San Andreas Fault is on such a boundary.
Note: New plate material is constantly created by the process of sea floor spreading, and old material is destroyed when two plates collide and one plate moves under the other.