| A | B |
|---|
| fossil | an imprint or mold of an ancient organism |
| Pangaea | a giant landmass that existed more than 200 million years ago |
| theory of continental drift | the continents were once joined together and have since drifted apart |
| mid-ocean ridge | an undersea mountain range where new ocean floor is produced |
| ocean-floor spreading | old ocean floor is pushed away from the mid-ocean ridge by the formation of new ocen floor |
| Alfred Wegener | responsible for the continent drift theory |
| trench | a V-shaped valley on the ocean floor where the old ocean floor is subducted |
| subduction | the crust plunges back into the mantle and melts |
| theory of plate tectonics | links the ideas of continental drift and ocean-floor spreading and explains how the Earth has changed over time |
| plate | a moving irregular slab that makes up the Earth's lithospere |
| tectonics | a branch of geology that deals with the movements that shpae the Earth's crust |
| lithosphere | the topmost solid part of the Earth |
| divergent boundary | a plate boundary where plates move apart |
| convergent boundary | a plate boundaryat which plate come together or collide with one another |
| strike-slip boundary | a plate boundary where two plates slip past one another horizontally |
| convection current | a movement of material caused by differences in temperature |
| Harry Hess | developed the theory of sea-floor spreading |
