| 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 landmass |
| 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 | theory that Earth's crust and upper mantle moves around on the asthenosphere |
| plate | a large section of Earth's oceanic or continental crust and rigid upper mantle that moves around on the astenosphere |
| lithosphere | rigid layer of Earth about 100km thick, made of the crust and a part of the upper mantle |
| asthenosphere | plastic like layer of Earth on which the lithosphereic plates float and move around |
| convection current | current in Earth's mantle that transfers heat in Earth's interior and is the driving force for plates tectonics |
| plate boundaries | where Earth's plates come together |
| divergent boundary | boundary between plates that are moving apart from one another |
| convergent boundaries | boundaries between Earth's plates that are moving together |
| subduction zone | where oceanic plates and continental plates collide, the oceanic plate is pushed beneath the continental plate |
| transform boundary | where two plates slide past one another |
| SONAR | device that uses sound waves to determine the depth of ocean and to map out the bottom of the ocean floor |
| mid-ocean ridge | area where new ocean floor is formed when lava erupts through cracks in the Earth's surface |
| Rift Valley | a large valley shaped by plates that are pulling apart |
| controversial | arguable, questionable |
