| A | B |
|---|
| crust | outermost layer of the Earth |
| mantle | layer of the Earth between the crust and the core |
| core | extends from the bottom of the mantle to the center of the Earth |
| lithosphere | outermost rigid layer of the Earth made up of the crust and the rigid upper part of the mantle |
| asthenosphere | soft layer of the mantle on which pieces of the lithosphere move |
| mesosphere | "middle sphere" or the strong lower part of the mantle |
| outer core | liquid layer of the Earth's core that lies beneath the mantle and surrounds the inner core |
| inner core | solid, dense center of our planet that extends from the bottom of the outer core to the center of the Earth |
| tectonic plates | pieces of the lithosphere that move around on top of the asthenosphere |
| continental drift | 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 as older materials are pulled away |
| 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 formed when two tectonic plates push into one another |
| divergent boundary | the boundary formed when two tectonic plates move away from each other |
| transform boundary | the boundary formed when two tectonic plates slide past each other |
| subduction zone | the region where oceanic plates sink down into the asthenosphere |
| 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 | stress that occurs when forces act to stretch an object |
| folding | when rock layers bend due to stress in the Earth's crust |
| fault | the surface along which rocks break and slide past each other |
| normal fault | occur when tectonic forces cause tension that pulls rocks apart |
| reverse fault | occurs when tectonic forces cause compression that push rocks together |
| strike-slip faults | occur when opposing forces cause rock to break and move horizontally |
| relative dating | determining whether an object or event is older or younger than other objects or events |
| superposition | principle that states that younger rocks lie above older rocks in undisturbed sequences |
| geologic column | an ideal sequence of rock layers that contains all the known fossils and rock formations on Earth arranged from oldest to youngest |
| unconformity | surface that represents a missing part of the geologic column |
| disconformity | exists where part of a sequence of parallel rock layers is missing |
| nonconformity | exists where sedimentary rock layers lie on top of an eroded surface of non-layered igneous or metamorphic rock |
| angular unconformity | exists between horizontal rock layers and rock layers that are tilted or folded. |
