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Vocabulary - Volcanoes, Earthquakes, Plate Tectonics, and Fossils

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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