| A | B |
|---|
| asthenosphere | A weak zone of the mantle directly below the lithosphere. Extends from 100-700 km. |
| continental drift | A theory that the continents are rafted about. Has been replaced by plate tectonics. |
| continental volcanic arc | Mountains formed in part by magma associated with the subduction of ocenaic crust below a continent. |
| convergent boundary | A boundary where two plates move together. |
| deep-ocean trench | A narrow, elongated depression on the floor of the ocean |
| divergent boundary | A region where the plates are moving apart. |
| hot spot | A concentration of heat in the mantle capable of producing magma. |
| lithosphere | The rigid outer layer of the Earth, including crust and upper mantle. |
| mid-oceanic ridge | A continuous mountain ridge on the floor of all major ocean basins. |
| normal polarity | A magnetic field that is the same as that which exists at present. |
| paleomagnetism | The natural remnant magnetism in rocks. |
| Pangaea | The proposed supercontinent that began to break aprt 200 mybp. |
| plate | One of many rigid sections of the lithosphere that moves as a unit. |
| plate tectonics | The theory that Earth's plates interact in various ways. |
| polar wandering | The apparent movement of the poles due to continents moving. |
| reverse polarity | A magneticfield opposite to that which exists today |
| rift | A region of Earth's crust along which divergence happens. |
| seafloor spreading | The process of producing new seafloor between two divergent plates. |
| transform fault boundary | A boundary where two plates slide past one another, neither creating nor destroying crust. |
| subduction zone | A long, narrow zone where one plate descends beneath another. |
| volcanic island arc | A chain of islands created by one ocean slab subducting beneath another. |
