| A | B |
|---|
| continental drift | the idea that the continents slowly moved over Earth's surface to their present locations |
| Pangaea | the name of the single landmass that may have existed long ago and broke apart giving rise to today's continents |
| mid-ocean ridge | an undersea mountain chain where new ocean floor may be produced |
| subduction | the process by which ocean floor sinks beneath a deep-ocean trench and back into the mantle |
| sea-floor spreading | the process by which molten material adds new oceanic crust to the ocean floor |
| deep-ocean trench | a deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle |
| plate tectonics | the theory that pieces of Earth's lithosphere are in constant motion, driven by convection currents in the mantle |
| fault | a break in Earth's crust where rocks have slipped past each other |
| divergent boundary | place where two plates move apart, or diverge |
| convergent boundary | place where two plates come together, or converge |
| rift valley | a deep valley that forms where two plates move apart; a deep valley that may form along a divergent boundary |
| transform boundary | place where two plates slip past each other; moving in opposite directions |
