| Term | Definition |
|---|
| continental drift | Wegener's hypothesis that all continents were once connected in a single large landmass that broke apart about 200 millions years ago and drifted slowly to their current positions |
| Pangaea | large, ancient landmass that was composed of all the continents joined together |
| seafloor spreading | Hess's theory that new seafloor is formed when magma is forced upward tward the surface at a mid-ocean ridge |
| plate tectonics | 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 athenosphere |
| lithosphere | ridgid layer of Earth about 100 km thick, made of the crust and part of the upper mantle |
| asthenoshere | plastic-like layer of Earth on which the lithospheric plates float and move around |
| convection current | current in Earth's mantle that transfers heat in Earth's interior and is driving force for the plate tectonics |
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