Plate Tectonics~ the theory that explains how large pieces of the lithosphere, called plates, move and change shape.
continental drift~the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations.
Pangaea~the supercontinent that formed 300 million years ago and that began to breakup 250 million years ago.
Asthenosphere~the solid, plastic layer of the mantle beneath the lithosphere; made of mantle rock that flows very slowly, which allows tectonic plates to move on top of it.
Litosphere~the solid, outer layer of earth that consists of the crust and the rigid upper part of the mantle.
Mid-Ocean ridge~a long, undersea mountain chain that has a step, narrow valley at its center, that forms as magma rises from the asthenosphere, and that creates new oceanic lithosphere (sea floor) as tectonic plates move apart.
Rift valley~a long narrow valley resulting from the subsidence of land between two parallel faults, often associated with volcanism.
Subduction~the process by which collision of the earths crustal plates results in one plates being drawn down or overridden by another, localized along