| A | B |
|---|
| crust | outermost, least dense layer of Earth |
| continental crust | thicker, less dense type of crust |
| oceanic crust | thinner, more dense type of crust |
| mantle | layer of Earth made up of magma that "flows" like asphalt |
| lithosphere | layer made up of the crust and upper part of the mantle |
| asthenosphere | plasticlike layer made up of the lower part of the mantle |
| outer core | layer of Earth made up of liquid nickel and iron |
| inner core | densest layer of Earth made of solid nickel and iron |
| plates | pieces of the Earth's crust |
| convection currents | process in which magma is heated, rises, then cools and sinks and causes the plates to move |
| continental drift | theory that all continents were once connected in a single, large landmass that broke apart and drifted slowly to their current positions |
| seafloor spreading | theory that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge |
| plate tectonics | theory that Earth's crust and upper mantle are broken into plates that float and move around on a plastic-like layer of the mantle |
| divergent boundary | point where two plates move away from each other |
| convergent boundary | point where two plates move towards each other |
| transform boundary | point where two plates slide past each other |
| earthquake | vibrations produced by the breaking of rock |
| normal fault | break in rock caused by tension forces, where rock above the fault surface moves down relative to the rock below the fault surface |
| reverse fault | break in rock caused by compression forces, where rock above the fault surface moves upward relative to the rock below the fault surface |
| strike-slip fault | break in rock caused by shear forces, where rocks move past each other without much vertical movement |
| seismic waves | waves generated by an earthquake |
| focus | point inside Earth where seismic waves are first released |
| primary waves | fastest waves in which particles in rocks move in the same direction as the wave |
| secondary waves | waves in which particles in rocks move perpindicular to the direction of the wave |
| surface waves | backward, rolling and side-to-side swaying waves caused when energy reaches Earth's surface |
| epicenter | point on Earth's surface above the focus |
| Richter scale | measures the magnitude of an earthquake |
| Mercalli scale | measures the intensity of an earthquake |
| volcano | opening in Earth that erupts gases, ash, and lava |
| vent | opening in which magma flows out of |
| crater | steep-walled depression around a volcano's vent |
| hot spot | unusually hot spot between mantle and core that forces magma to the surface |
| shield volcano | broad, gently sloping volcano formed by quiet eruptions of basaltic lava |
| cinder cone volcano | steep-sided, loosely packed volcano formed when tephra falls to the ground |
| composite volcano | built by alternating explosive and quiet eruptions that produce layers of tephra and lava |
