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Seismic Waves
Vibrations that travel through Earth carrying the energy released during an earthquake.
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Pressure
The force exerted on a surface divided by the area over which the force is exerted.
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Crust
The crust is a layer of solid rock that includes both dry land and the ocean floor.
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Basalt
Oceanic crust consists mostly of rocks such as basalt. Basalt is dark rock with a fine texture.
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Granite
Continental crust, the crust that forms the continents, consists mainly of rocks such as granite. Granite is a rock that usually is a light color and has a coarse texture.
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Mantle
The layer of hot, solid material between Earths crust and core.
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Lithosphere
A rigid layer made up of the uppermost part of the mantle and the crust.
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Asthenosphere
The soft layer of the mantle on which the lithosphere floats.
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Outer Core
A layer of molten iron and nickel that surrounds the inner core of Earth.
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Inner Core
A dense sphere of solid iron and nickel at the center of Earth.
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Radiation
The transfer of energy through space.
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Conduction
The transfer of heat within a material or between materials that are touching.
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Convection
The transfer of heat by movement of a fluid.
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convection current
The movement of a fluid, caused by differences in temperature, that transfers heat from one part of the fluid to another.
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Density
The amount of mass in a given space; mass per unit volume.
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Continental Drift
The hypothesis that the continents slowly move across Earth’s surface.
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Pangaea
The name of the single landmass that broke apart 200 million years ago and gave rise to today’s continents.
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Fossil
A trace of an ancient organism that has been preserved in rock.
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Mid-ocean Ridge
An undersea mountain chain where new ocean floor is produced; a divergent plate boundary.
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Sonar
A device that determines the distance of an object under water by recording echoes of sound waves.
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Sea-floor Spreading
The process by which molten material adds new oceanic crust to the ocean floor.
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Deep-Ocean Trench
A deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.
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Subduction
The process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.
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Plate
A section of the lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust.
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Scientific Theory
A well-tested concept that explains a wide range of observations.
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Plate Tectonics
The theory that pieces of Earth_tm)s lithosphere are in constant motion, driven by convection currents in the mantle.
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Fault
A break in Earth’s crust where masses of rock slip past each other.
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Divergent Boundary
A plate boundary where two plates move away from each other.
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Rift Valley
A deep valley that forms where two plates move apart.
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Convergent Boundary
A plate boundary where two plates move toward each other.
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Transform Boundary
A plate boundary where two plates move past each other in opposite directions.
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