plate tectonics

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A theory that explains the global distribution of geological phenomena such as seismicity, volcanism, continental drift, and mountain building in terms of the formation, destruction, movement, and interaction of the earth's lithospheric plates.
• noun The dynamics of plate movement.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Geol.) A geological theory which holds that the crust of the earth (the lithosphere) is divided into a small number of large separate plates which float and move slowly around on the more plastic asthenosphere, breaking apart and moving away from each other at points where magma upwells from below, and, driven by such upwellings and other currents on the athenosphere, sliding past each other, colliding with each other, and in some cases being submerged (subducted) one below the other. This theory is now widely accepted, and explains many geological phenomena such as the clustered locations of earthquakes, mountain building, volcanism, and the similarities observed between the geology of continents, such as South America and Africa which are now far apart, but, according to the theory, were once joined together. The motions of such tectonic plates are very slow, typically only several centimeters per year, but over tens and hundreds of millions of years, cause very large changes in the relative positions of the continents. The consequence of such movement of plates is called continental drift.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun geology The large-scale movement of tectonic plates that contributes to continental drift.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the branch of geology studying the folding and faulting of the earth's crust