| A | B |
|---|
| Asthenosphere | A subdivision of the mantle situated below the lithosphere. |
| Continental drift theory | A theory that originally proposed that the continents are rafted about. |
| Continental volcanic arc | Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. |
| Convergent boundary | A boundary in which two plates move together, causing one of the slabs of |
| Deep-ocean trench | A narrow, elongated depression on the floor of the ocean. |
| Divergent boundary | A region where the rigid plates are moving apart, typified by the mid-oceanic ridges. |
| Hot spot | A concentration of heat in the mantle capable of producing magma which, in turn, extrudes onto Earth's surface. |
| lithosphere | The rigid outer layer of the earth, including the crust and upper mantle. |
| Mid-ocean ridge | A continuous mountainous ridge on the floor of all the major ocean basins |
| Normal polarity | A magnetic field that is the same as that which exists at present. |
| Paleomagnetism | The permanent magnetization acquired by rock that can be used to determine the location of the magnetic poles and the latitude of the rock at the time it became magnetized. |
| Pangaea | The proposed supercontinent that 200 million years ago began to break apart and form the present landmasses. |
| Plate | One of numerous rigid sections of the lithosphere that moves as a unit over the material of the asthenosphere. |
| Plate tectonics | The theory that proposes that Earth's outer shell consists of individual plates |
| Polar wandering | either the magnetic poles migrated greatly through time or the continents had gradually shifted their positions. |
| Reverse polarity | A magnetic field opposite to that which exists at present |
| Rift zone | A region of Earth' s crust along which divergence is taking place. |
| Seafloor spreading | The process of producing new seafloor between two diverging plates. |
| Subduction zone | A long, narrow zone where one lithospheric plate descends beneath another. |
| Transform boundary | A boundary in which two plates slide past one another without creating or |
| Volcanic island arc | A chain of volcanic islands generally located a few hundred kilometers from a trench where active subduction of one oceanic slab beneath another is occurring. |
