| A | B |
|---|
| continental drift | hypothesis that states that continents have moved slowly to their current locations on Earth |
| Pangaea | single, large landmass made up of all the continents connected together that broke apart about 200 million years ago |
| seafloor spreading | theory that magma from below Earth's crust is forced upward toward the surface at a mid-ocean ridge, flows from the cracks as the seafloor spreads apart, and becomes solid as it cools, forming new seafloor |
| plate | sections of Earth's lithosphere that are composed of oceanic crust, continental crust, and rigid upper mantle and that move around on a plasticlike layer of the mantle |
| asthenosphere | plastic-like layer below the lithosphere |
| lithosphere | rigid, outermost layer of Earth that is about 100 km thick, and is composed of the crust and part of the upper mantle |
| convection current | cycle of heating, rising, cooling, and sinking that is thought to be the force behind plate tectonics |
| Alfred Wegner | Suggested that all the continents were joined together at some point in the past. In 1912 proposed the idea of continental drift. |
| Harry Hess | In the 1960's this scientist formulated the seafloor spreading theory. |
| magnetometer | a sensitive instrument that records magnetic data |
| Glomar Challenger | research ship that drilled for rocks in the seafloor so that scientists could study the age of the rocks |
| divergent boundary | the boundary between 2 plates that are moving apart |
| convergent boundary | the boundary between 2 plates that are moving together (colliding) |
| subduction zone | the area where an oceanic plate is pushed down into the upper mantle |
| transform boundary | the boundary between 2 plates whre the plates are sliding past one another; they move either in opposite directions or in the same direction at different rates |
