| A | B |
|---|
| crust | the layer of rock that is the outer layer of the Earth |
| mantle | the layer of hot material between the Earth's crust and outer core |
| inner core | a ball of solid metal in the center of the Earth |
| outer core | a layer of liquid metal that surrounds the inner core of the Earth |
| Pangaea | the one large land mass that broke apart 200 million years ago and formed the continents |
| continental drift | the theory that the continents slowly move across Earth's surface |
| subduction | the process where some of the Earth's crust sinks back down into the mantle |
| sea-floor spreading | the process where molten material rises to the surface of the Earth and forms new crust on the ocean floor |
| plate tectonics | the theory that the Earth's surface is broken into pieces, called plates, that are in constant motion |
| transform boundary | a plate boundary where two plates slide past each other in the opposite direction |
| divergent boundary | a plate boundary where two plates move apart from each other |
| convergent boundary | a plate boundary where two plates move towards each other |
