Plate Tectonics: A theory of global tectonics in which the lithosphere is divided into a number of crustal plates, each of which moves on the plastic asthenosphere more or less independently to collide with, slide under, or move past adjacent plates.
Continental Drift: The lateral movement of continents resulting from the motion of crustal plates.
Pangaea: The hypothetical landmass that existed when all continents were joined, from about 300 to 200 million years ago.
Asthenosphere: The region below the lithosphere, variously estimated as being from fifty to several hundred miles (eighty-five to several hundred kilometers) thick, in which the rock is less rigid than that above and below but rigid enough to transmit transverse seismic waves.
Lithosphere: the solid portion of the earth (distinguished from atmosphere, hydrosphere ).
Mid-Oceanic ridge: A is a Mid-Oceanic ridge general term for an underwater mountain system that consists of various mountain ranges (chains), typically having a valley known as a rift running along its spine, formed by plate tectonics.
Rift valleys: A subsea chasm extending along the crest of a mid-ocean ridge, locus of the magma upwellings that accompany seafloor spreading.
Subduction: Geology . the process by which collision of the earth's crustal plates results in one plate's being drawn down or overridden by another, localized along the juncture (subduction zone) of two plates.