Plate Tectonics Plate tectonics is the theory that the lithosphere (the outer part of solid Earth) is divided into a small number of plates that float on and travel independently over the Earth's mantle. Much of the Earth's seismic activity and volcanism, along with mountain-building processes, occurs at the boundaries of these plates. The surface of the Earth is composed of about a dozen large plates and several small ones. Within each plate the rocks …showed first 75 words of 1927 total…

…showed last 75 words of 1927 total…in any detail the implications of the plate-tectonic theory for the evolution of continental orogenic belts; most thought had been devoted to the oceans. In 1969 John Dewey of the University of Cambridge outlined an analysis of the Caledonian-Appalachian orogenic belts in terms of a complete plate-tectonic cycle of events, and this provided a model for the interpretation of other pre-Mesozoic (Paleozoic and Precambrian) belts. For a detailed discussion of plate-tectonic theory and its far-reaching effects,