| Term | Definition |
|---|
| crust | Earth's outermost layer, which varies in thickness from about 5km to 60km and is separated from the mantle by the Moho Discontinuity |
| epicenter | point of Earth's surface directely above an earthquake's focus |
| focus | in an earthquake, the point beneath Earth's surface where energy release occurs |
| inner core | very dense, solid center od the Earth that is made of mostly iron with smaller amounts of oxygen, silicon, sulfur, or nickel |
| magnitude | measure of the energy released by an earthquake |
| mantle | largest layer inside Earth, lying directly above the outer core and that is made mostly of silicon, oxygen, magnesium, and iron |
| normal fault | break in rock due to tension forces, where rock above the fault surface moves downward in relation to rock below the fault surface |
| outer core | liquid core that surrounds Earth's solid inner core, and that is made mostly of iron |
| primary waves | waves that travel outward from an Earthquake's focus and cause particles in rocks to move back and forth in the same direction the wave is moving |
| reverse fault | break in rock due to compression forces, where rocks above the fault surface move upward and over the rocks below the fault surface |
| secondary waves | waves that travel outward from an earthquke's focus and move through Earth by causing particles in rocks to vibrate at right angles to the direction of the wave |
| seismic waves | energy waves that are produced at and travel outward from the earthquake's focus |
| seismograph | device used by seimologists to record primary, secondary, suface waves from earthquakes |
| seismologist | scientist who studiesearthquakes and seismic waves |
| strike-slip fault | break in rock due to shearing forces, where rocks on either side of the fault suface move past each other with little upward or downward movement |
| athenosphere | plastic-like layer below the lithosphere |
| continental drift | hypothesis proposed by Alfred Wegener that the states that continents have moved slowly to their current locations on Earth |
| convection current | cycle of heating, rising, cooling, and sinking that is thought to be the force behind plate tectioncs |
| lithosphere | rigid, outermost layer of Earth that is about 100km thick, and is composed of the crust and part of the upper mantle |
| pangaea | single large landmass made up of all the continents connected together that broke apart 200 million years ago |
| plate | surface along which rocks break and move |
| plate tectonics | theory that Earth's crust and upper mantle are broken into sections that move around on a plastic-like layer of the mantle |
| seafloor spreading | theory that magma from below Earth's crust is forced upward toward the surface at a mid-ocean ridge, flows from the cracks as the seafloor spreads apart and bcomes solid as it cools, forming new seafloor |
| surface waves | waves of energy that reach Earth's surface during an earthquake, travel outward from the epicenter, and move rock particles up and down, and side to side |
| tsunami | powerful seismic sea wave that can travel thousands of kilometers in all directions and that begins over an earthquake focus |
| batholith | largest intrusive igneous rock bodies that form when magma cools underground before reaching Earth's surface |
| caldera | large opening formed when the top of a volcano collapes |
| cinder cone volcano | steep-sided volcano made of loosely packed tephra |
| composite volcano | a volacano formed by alternating layers of tephra and lava and that is found mostly where Earth's plates come together |
| crater | steep-walled depression around a volcano's vent |
| dike | intrusive igneous rock body formed when magma is squeezed into a vertical crack that cuts across rock layers and hardens |
| hot spot | location in the mantle that is hotter than any other areas and that melts rock, which is forced up toward the crust as magma |
| shield volcano | a broad volcano with gently sloping sides |
| sill | intrusive igneous rock body formed when magma is squeezed into a horizontal crack that cuts across rock layers and hardens |
| volcanic neck | solid, igneous core of a volcano left behind when a volacno stops erupting |
| vent | an opening on Earth's surface where magma is forced up and flows out as lava |
| volcano | opening in Earth's surface that often forms a mountain when layers of lava and volcanic ash erupt and build up |
| earthquake | vibrations caused by breaking rocks along faults |
| fault | surface along which rocks break and move |
| tephra | bits of rock or solified lava dropped from the air |
| fossils | remains or traces of a once living organism reserved by rock |
| pertified remains | fossils that form when some or all of the original materials that made up the organisms are replaced with minerals |
| carbonaceous film | fossil formed when the remains of a once living organism are subjected to heat and pressure, leaving only a thin film of carbon behind |
| mold | fossil formed when an organism is buried, decays, and leaves behind a hollow place in rock |
| cast | fossil formed when sediments fill in a mold and harden into rock |
| index fossil | fossil of a species that existed on Earth for only a short time, were abundant, and were widespread geographically |
| principle of superposition | states that for undisturbed layers of rock, older rocks lie underneath younger and younger rocks |
| relative dating | method to determine the order of events and relative age of rocks by examining the position of rocks in a sequence |
| unconformity | gaps in the rock layers due to erosion, nondeposition, or both |
| absolute dating | process that uses the properties of atoms in rocks and other objects to determine their exact ages, in years |
| radioactive decay | release of nuclear particles and energy from unstable atomic nuclei |
| half-life | time needed for one half-life the mass of a sample of a radioactive isotope to decay |
| uniformitarianism | states that Earth processes happening today are similar to those that happened in the past |
| radioactive dating | process to determine the absolute ages of rocks by measuring the amounts of parent and daughter materials in a rock |
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