| A | B |
|---|
| lithosphere | The layer of earth that makes up tectonic plates. |
| convection current | The movement of matter due to differences in density. |
| continental drift | The hypothesis that the continents were once connected, but broke apart and drifted to where they are now. |
| Pangaea | The name of the single landmass that broke apart 200 million years ago and gave rise to today's continents |
| mid-ocean ridge | An underwater mountain chain formed when tectonic plates separate. |
| sea-floor spreading | Theory that new seafloor is formed when plates separate. |
| subduction zone | The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary |
| plate | A section of the lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust |
| plate tectonics | The theory that pieces of Earth's lithosphere are in constant motion, driven by convection currents in the mantle |
| divergent boundary | A plate boundary where two plates move away from each other |
| convergent boundary | A plate boundary where two plates move toward each other |
| transform boundary | A plate boundary where two plates move past each other in opposite directions |
