subduction		deep valley that forms where two plates move apart
constructiveforce		theory that the pieces of Earth's lithosphere are in constant motion, driven by convection currents in the mantle
divergentboundary		name of the single landmass that broke apart 200 million years ago and gave rise to today's continents
seafloorspreading		soft layer of the mantle on which the lithosphere floats
convergentboundary		the undersea mountain chain where new ocean floor is produced; a divergent plate boundary
asthenosphere		process by which molten material adds new oceanic crust to the ocean floor
lithosphere		force that slowly wears away mountains and other features on the surface of the Earth
riftvalley		plate boundary where two plates move toward each other
Pangaea		plate boundary where two plates move past each other in opposite directions
platetectonics		force that builds up mountains and landmasses on Earth's surface
midoceanridge		transfer of heat by movements of a heated fluid
transformboundary		movement of energy from a warmer object to a cooler object
destructiveforce		plate boundary where two plates move away from each other
heattransfer		process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary
convection		rigid layer made up of the uppermost parth of the mantle and the crust