| A | B |
|---|
| Continental drift | Wegener’s hypothesis that all continents were once connected in a single large landmass that broke apart about 200 million years ago and drifted slowly to their current positions |
| Pangaea | Large ancient land mass that was composed of all the continents joined together |
| Crust | The rocky outer layer of Earth; 10 to 50 km thick |
| Mantle | The layer of Earth composed of solid and partially molten rock that is rich in magnesium and iron and is located between the crust and the core; 2,900 km thick |
| Lithosphere | Rigid layer of Earth about 100 km thick, made of the crust and a part of the upper mantle |
| Asthenosphere | The plastic-like layer of the mantle on which the lithospheric plates float and move around |
| Seafloor spreading | Hess’s theory that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge |
| Plate tectonics | The theory that Earth’s crust and upper mantle are broken into plates that float and move around on a plastic-like layer of the mantle |
| Plate | A large section of Earth’s oceanic or continental crust and rigid upper mantle that moves around on the asthenosphere |
| Convection current | Movement in Earth’s mantle that transfers heat in Earth’s interior and is the driving force for plate tectonics |
| Divergent boundary | A boundary between tectonics plates that are moving away from each other |
| Convergent boundary | A boundary between tectonic plates that are moving toward each other |
| Subduction zone | The area along a convergent boundary where a dense oceanic plate sinks beneath a less dense continental plate |
| Transform boundary | A boundary between tectonic plates that are sliding past one another |
