deep ocean trenches
a deep valley along the ocean floor through which oceanic crust slowly sinks towards the mantle
mid-ocean ridge
the undersea mountain chain where new ocean floor is produced; a divergent plate boundary
convection current
the movement of a fluid, caused by differences in temperature, that transfers heat from one part of the fluid to another.
asthenosphere
the soft layer of the mantle on which the lithosphere floats
lithosphere
a rigid layer made up of the uppermost part of the mantle and the crust.
continental drift
the hypothesis that the continents slowly move across Earth's surface.
convergent boundary
a plate boundary where two plates move toward each other.
subduction
the process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.
magnetic stripes
magnetized stripes that hold a record of reversals in Earth's magnetic field; it occurs on the ocean floor
sea-floor spreading
the process by which molten material adds new oceanic crust to the ocean floor
rift valleys
a deep valley that forms where two plates move apart.
divergent boundary
a plate boundary where tow plates move away from each other
transform boundary
a plate boundary where two plates move past each other in opposite directions
fault
a break in Earth's crust where slabs of rock slip past each other
pangaea
the name of the single landmass that broke apart 200 million years ago and gave rise to today's continents
plates
a section of the lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust.