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.
Before Now
Before Now
Pangaea: the super continent that formed 300 million years ago and that began to break up beginning 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.
Lithosphere: the solid, outer layer of Earth that consists of the crust and rigid upper part of the mantle.
Mid-ocean ridge: a long. undersea mountain chain that has a steep, 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: the process by which Earth's crust breaks apart; can occur within continental crust or oceanic crust.
Subduction: the region along a plate boundary where one plate moves under another plate