Unit 7 Vocabulary Continental Drift - A hypothesis that originally proposed that the continents had once been joined to form a super continent; The supercontinent broke into pieces, which drifted into their present day positions. Pangaea - The proposed supercontinent that 200 million years ago began to break apart and form the present landmasses. Plate Tectonics - The theory that proposes that Earth’s outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanos, mountains, and the crust itself. Plate - One of numerous rigid sections of the lithosphere that moves as a unit over the material of the asthenosphere.

Divergent Boundary - This type of boundary occurs when two plates move apart. Convergent Boundary - This type of boundary occurs when two plates move together. Transform Fault Boundary - These are margins where two plates grind past each other without the production or destruction of the lithosphere.

Oceanic Ridge - An oceanic ridge is a continuous elevated zone on the floor of all the major ocean basins and vary in width from 1000 to 4000 kilometers. The rifts at the crests of ridges represent divergent plate boundaries.