| 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. |
| basalt | A dark, dense, igneous rock with a fine texture, found in oceanic crust |
| granite | A usually light-colored igneous rock that is found in continental crust |
| 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 transfer of energy through space |
| conduction | The transfer of heat within a material or between materials that are touching. |
| convection | The transfer of heat by movement of a fluid |
| density | The amount of mass in a given space; mass per unit volume |
| convection current | The movement of a fluid, caused by differences in temperature, 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 toward 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. |
| scientific theory | A well-tested concept that explains a wide range of observations. |
| plate tectonics | The theory that pieces of Earth_tm)s lithosphere are in constant motion, driven by convection currents in the mantle. |
| fault | A break in Earth’s crust where masses of rock slip past each other |
| divergent boundary | A plate boundary where two plates move away from each other. |
| rift valley | A deep valley that forms where two plates move apart |
| convergent boundary | A plate boundary where two plates move toward each other. |
| transform boundary | A plate boundary where two plates move past each other in opposite directions. |
