Tectonics

Tectonics, branch in geology that studies the earth's structural deformations, the forces involved, and the resulting forms. The most popular theory used to explain the origin of tectonic forces is the plate tectonic theory, developed in the 1960s. This theory holds that the movement of the rigid plates that line the surface of the earth's outer shell (either aigainst one other or away from one another) produces the crustal deformations in the earth. A second theory contends thet the earth originated from molten rock, which cooled as it shrunk; this shrinking in turn produced the tectonic forces. A third theory maintains that the earth began as a cold mass, and as it warmed it produced forces that fractured the crust.

See also: Volcano.