| Question |
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| Answer |
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| continental drift |
wegener's hypothesis that all continents were once connected in a single large landmass that broke apart about 200 million years ago and drifted slowly to their current positions |
| pangea |
large, ancient landmass that was composed of all the continents joined together |
| seafloor spreading |
Hess's theory that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge |
| plate tectonics |
theory the earth's crust and upper mantle are broken into plates that float and move around on a plastic like layer of the mantle |
| plate |
a large section of earth's oceanic or continental crust and rigid upper mantle that moves around on the asthenosphere |
| convection current |
current in earth's mantle that transfers heat in earth's interior and is the driving force for plate tectonics |
| earthquake |
vibrations produced when rocks break along a fault |
| primary waves |
seismic wave that moves rock particles back-and-forth in the same direction that the wave travels |
| secondary waves |
seismic wave that moves rock particles at right angles to the direction of the wave |
| surface waves |
seismic wave that move rock particles up-and-down in a backward rolling motion and side-to-side in a swaying motion |
| epicenter |
point on earth's surface directly above an earthquake's focus |
| seismograph |
instrument used to register earthquake waves and record the time that each arrived |
| volcano |
opening in earth's surface that erupts sulfurous gases,ash,and lava; can form at earth's plate boundaries, where plates move apart or together, and at hot spots |
| vent |
opining where magma is forced up and flows out onto earth's surface as lava, forming a volcano |
| crater |
steep-walled depression around a volcano's vent |
| hot spot |
the result of an unusually hot area at the boundary between earth's mantle and core that forms volcanoes when melted rock is forced upward and breaks through the crust |
| 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 |
volcano builtby alternating explosive and quiet eruptions that produce layers of tephra and lava; found mostly where earth's plates come together and one plate sinks below the other |
| tephra |
bits of rock or solidified lava dropped from the air during an explosive volcanic eruption;ranges in size from volcanic ash to volcanic bombs and blocks |
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