| A | B |
|---|
| crust | the thin, outermost layer of the Earth |
| 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, uppermost part of the mantle |
| asthenosphere | the partially molten layer of the upper mantle on which the tectonic plates of the lithosphere move |
| mesosphere | literally, the "middle sphere"-the ridid, lower part of the mantle between the asthenosphere and the outer core |
| outer core | the liquid layer of the Earth's core between the mesosphere and the inner core |
| inner core | the solid, dense, spherical center of the Earth |
| tectonic plates | huge pieces of the lithosphere that move around on top of the asthenosphere |
| continental drift | the theory that continents can drift apart from one another and that they have done so in the past |
| sea-floor spreading | the process by which new oceanic crust forms at mid-ocean ridges as tectonic plates are pulled away from each other |
| plate tectonics | the theory that the Earth's lithosphere is divided into tectonic plates that move around on top of the asthenosphere |
| convergent boundary | the boundary between two colliding tectonic plates |
| subduction zone | the region where an oceanic plate sinks down into the asthenosphere at a convergent boundary, usually between continental and oceanic plates |
| divergent boundary | the boundary between two tectonic plates that are sliding past each other horizontally |
| transform boundary | the boundary between two tectonic plates that are sliding past each other horizontally |
| stress | the amount of force per unit area placed on a given material |
| compression | stress that occurs when opposing forces apply pressure to a given material |
| tension | stress that occurs when opposing forces stretch a material |
| folding | the bending of rock layers due to stress caused by movements in the Earth's crust |
| fault | a break in the Earth's crust along which two blocks of the crust slide relative to each other due to tectonic forces |
| 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 |
