| A | B |
|---|
| mid-Atlantic ridge | a midocean ridge in the Atlantic Ocean |
| molten rock | liqid rocks |
| Pangaea | the single giant landmass that existed more that 200 million years ago, and that gave rise to the present-day continents |
| Ring of Fire | the earthquake and volcano zone that encircles the Pacific Ocean |
| convergent boundary | a plate boundary at which plates come together |
| divergent boundary | a plate boundary at which the plates move apart |
| mantle | the layer of Earth that extends from the bottom of the crust to the core |
| fault | a brake or crack along which rocks move |
| magma | molten rock beneath the Earth's surface |
| ocean floor spreading | the process in which old ocean floor is pushed away from a midocean ridge by the formation of a new ocean floor |
| convection currents | a movement of material caused by differences in temperature |
| hot spots | a column of sizzling rock thatrises from the mantle |
| trench | a V-shaped valley on the ocean floorwhere old ocean floor is subducted |
| lithospheric plate | plates that are made up of the crust and upper mantle |
| seismograph | an instrument that detects and measures sesmic waves |
| Ricther Scale | the scale used to measure the strength of earthquakes |
