continental drift and sea-floor spreading, Plate tectonics terms

rift valley

A deep valley where two plates move apart

deep-ocean trench

deep under water canyon formed as oceanic plate sinks into the mantle

mid-ocean ridge

An undersea mountain chain where new ocean floor is made

lithosphere

A rigid layer made up of the uppermost part of the mantle and the crust.

asthenosphere

The soft layer of the mantle on which the lithosphere floats.

convection current

a current caused by the rising of heated fluid and sinking of cooled fluid

sea-floor spreading

the creation and movement of new oceanic crust at mid-ocean ridges

subduction

process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle

Pangaea

large, ancient landmass that was composed of all the continents joined together

divergent boundary

where plates move apart or separate

transform boundary

where plates slip or slide past each other

convergent boundary

where plates move together (collide, crash)

plate

a large piece of Earth's lithosphere that is in constant, slow motion due to convection currents in the mantle

continental drift

The hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations

earthquake

The shaking that results from the movement of rock beneath Earth's surface.

fault

A break in the earth's crust

plate tectonics

A theory stating that the earth's surface is broken into plates that move.

seismic waves

a wave in the earth produced by an earthquake