| A | B |
|---|
| CRUST | The layer of rock that forms Earth's outer surface. |
| MANTLE | The layer of hot, solid material between Earth's crust and core. |
| OUTER CORE | A layer of molten iron and nickel that surrounds the inner core of Earth. |
| CONVECTION CURRENT | The movement of a fluid, caused by differences in temperature, that transfers heat from one part of the fluid to another. |
| PANGAEA | The name of the single landmass that broke apart 225 million years ago and gave rise to today's continents. |
| CONTINENTAL DRIFT | The hypothesis that the continents slowly move across Earth's surface. |
| FOSSIL | The preserved remains or traces of living things. |
| MID-OCEAN RIDGE | The undersea mountain chain where new ocean floor is produced; a divergent plate boundary. |
| SEA-FLOOR SPREADING | The process by which molten material adds new oceanic crust to the ocean floor. |
| TRENCH | A deep valley along the ocean floor through which oceanic crust slowly sinks toward the mantle. |
| SUBDUCTION | 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. |
| TRANSFORM BOUNDARY | A plate boundary where two plates move past each other in opposite direction. |
| DIVERGENT BOUNDARY | A plate boundary where two plates move away from each other. |
| RIFT VALLEY | A deep valley that forms where two plates move apart. |
| CONVERGENT BOUNDARY | A plate boundary where two plates move toward each other. |
| ALFRED WEGENER | Proposed theory in 1915 that earths continents were moving |
