| A | B |
|---|
| seismic waves | vibrations that travel through Earth carrying the energy released during an earthquake. |
| pressure | the force exerted on a surface divided by the area over which the force is exerted. |
| crust | the layer of rock that forms Earth's outer surface |
| mantle | the layer of hot, solid material between Earth's crust and core. |
| lithosphere | a rigid layer made up of the uppermost part of the mantle and the crust. |
| asthenosphere | the soft layer of the mantle on which the lithosphere floats. |
| outer core | a layer of molten iron and nickel that surrounds the inner core of Earth. |
| inner core | a dense sphere of solid iron and nickel at the center of Earth. |
| radiation | the direct transfer of energy by electromagnetic waves. |
| conduction | the direct transfer of thermal energy from one substance to another that it is touching. |
| convection | the transfer of heat by movement of a fluid. |
| density | the amount of mass of a substance in a given volume. |
| convection current | the movement of a fluid, caused by differences in temperatures, that transfers heat from one part of the fluid to another. |
| continental drift | the hypothesis that the continents slowly move across Earth's surface. |
| Pangaea | the name of the single landmass that broke apart 200 million years ago and gave rise to today's continents. |
| fossil | a trace of an ancient organism that has been preserved in rock. |
| mid-ocean ridge | an undersea mountain chain where new ocean floor is produced; a divergent plate boundary. |
| sonar | a device that determines the distance of an object under water by recording echoes of sound waves. |
| sea-floor spreading | the process by which molten material adds new oceanic crust to the ocean floor. |
| deep-ocean trench | a deep valley along the ocean floor beneath which oceanic crust slowly sinks into the mantle. |
| subduction | the process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary. |
| plate | a section of the lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust. |
| plate tectonics | the theory that pieces of Earth's lithosphere are in constant motion, driven by convection currents in the mantle. |
| fault | a break or crack in Earth's lithosphere along which the rocks move. |
| spreading boundary | a plate boundary where two plates move away from each other. Also called a divergent boundary. |
| rift valley | a deep valley that forms where two plates move apart. |
| colliding boundary | a plate boundary where two plates move toward each other. Also called a convergent boundary. |
| sliding boundary | a plate boundary where two plates move past each other in opposite directions. |
