| A | B |
|---|
| crust | the Earth's outermost layer |
| mantle | the layer directly beneath the Earth's crust |
| core | the Earth's innermost layer |
| lithosphere | the cool, solid portion of Earth that includes all the crust and part of the upper mantle |
| asthenosphere | a zone of partially melted rock in the upper mantle of the Earth |
| plate tectonics | the theory scientists use to explain the movements of the plates on the Earth's surface |
| divergent boundary | a boundary where crustal plates move away from each other |
| convergent boundary | a boundary where crustal plates collide with each other |
| transform fault boundary | a boundary where crustal plates grind past each other |
| mid-ocean ridge | the place where plates of the Earth's crust along the ocean floor are being split apart and molten rock pushes up to form new ocean floor and a mountain range |
| rift | a deep ocean valley formed where two crustal plates move apart |
| sea-floor spreading | a process in which magna is slowly pushed up through cracks in a rift and then cools to form new sea floor |
| earthquake | the sudden movement of rock along a fault which releases energy vibrations |
| focus | the point in the Earth's crust where the first major movement of an earthquake fault occurs |
| epicenter | the point on the Earth's surface directly above the focus of an earthquake |
| P wave | a primary wave or "push-pull" wave of released energy in the Earth's surface that causes a back-and forth vibration in the same direction that the wave moves |
| S wave | a slower kind of energy wave released by an earthquake that causes vibrations at right angles to the wave's direction of travel |
| surface wave | an energy wave from an earthquake that travels only at the surface and moves less quickly than P waves and S waves but makes the ground roll and sway |
| Richter scale | a scale that measures the amount of energy released during an earthquake |
| volcano | a mountain that may form around an opening in the Earth's surface where an eruption or molten rock occurs |
