| A | B |
|---|
| crust | the thin, outermost layer of the Earth, or the uppermost part of the lithosphere |
| mantle | the layer of the Earth between the crust and the core |
| core | the central, spherical part of the Earth below the mantle |
| lithosphere | the outermost, rigid layer of the Earth that consists of the crust and the rigid upper part of the mantle |
| asthenosphere | the soft layer of the mantle on which pieces of the lithosphere move |
| mesosphere | literally, the "middle sphere"-the strong, lower part of the mantle between the asthenosphere and the outer core |
| outer core | the liquid layer of the Earth's core that lies beneath the mantle and surrounds the inner core |
| inner core | the solid, dense center of the Earth |
| tectonic plate | a piece of the lithosphere that moves around on top of the asthenosphere |
| continental drift | the theory that continents can drift apart from one another and have done so in the past |
| sea-floor spreading | the process by which new oceanic lithosphere is created at mid-ocean ridges as older materials are pulled away from the ridge |
| plate tectonics | the theory that the Earth's lithosphere is devided into tectonic plates that move around on top of the asthenoshere |
| convergent boundary | the boundary between two colliding tectonic plates |
| subduction zone | the region where an oceanic plate sinks down into the asthenosphere at the convergent boundary, usually between continental and oceanic plates |
| divergent boundary | the boundary between two tectonic plates that are moving away from each other |
| transform boundary | the boundary between two tectonic plates that are sliding past each other horizontally |
| stress | the amount of force per unit area that is put on a given material |
| compression | the type of stress that occurs when an object is squeezed |
| tension | the type of stress that occurs when forces act to stretch an object |
| folding | the bending of rock layers due to stress in the Earth's crust |
| fault | a break in the Earth's crust along which two blocks of the crust slide relative to one another |
| normal fault | a fault in which the hanging wall moves down relative to the footwall |
| reverse fault | a fault in which the hanging wall moves up relative to the footwall |
| strike-slip fault | a fault in which the two fault blocks move past each other horizontally |
