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Earth's outermost layer, which varies in thickness from about 5km to 60km and is separated from the mantle by the Moho Discontinuity


point of Earth's surface directely above an earthquake's 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


measure of the energy released by an earthquake


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


device used by seimologists to record primary, secondary, suface waves from earthquakes


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


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


rigid, outermost layer of Earth that is about 100km thick, and is composed of the crust and part of the upper mantle


single large landmass made up of all the continents connected together that broke apart 200 million years ago


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


powerful seismic sea wave that can travel thousands of kilometers in all directions and that begins over an earthquake focus


largest intrusive igneous rock bodies that form when magma cools underground before reaching Earth's surface


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


steep-walled depression around a volcano's vent


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


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


an opening on Earth's surface where magma is forced up and flows out as lava


opening in Earth's surface that often forms a mountain when layers of lava and volcanic ash erupt and build up


vibrations caused by breaking rocks along faults


surface along which rocks break and move


bits of rock or solified lava dropped from the air


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


fossil formed when an organism is buried, decays, and leaves behind a hollow place in rock


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


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


time needed for one half-life the mass of a sample of a radioactive isotope to decay


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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