Chapter 7 Continental Drift & Plate Tectonics

I continental drift

hypothesis that continents are in constant motion

fossil

naturally preserved remains, imprints, or traces of organisms

Pangaea

ancient supercontinent, made up of all the land of today's continents

magnetic reversal

event in which the magnetic field reverses direction

mid-ocean ridge

mountain range located on the seafloor under the oceans

normal polarity

today's magnetic field; magnets orient themselves to point north

reversed polarity

in the opposite direction, and the north end of the magnetic field is close to the present-day south pole; still a magentic field in which magnets orient to point north

seafloor spreading

new oceanic crust forms at a mid-ocean ridge as old oceanic crust moves away

convection

circulation of material caused by differences in temperature and density

convergent plate boundary

area where two plates collide

divergent plate boundary

area where two plates separate

transform plate boundary

area where two plates slide past each other

lithosphere

cold, rigid outermost rock layer of Earth

plate tectonics

theory that Earth's surface is made of rock plates that move with respect to each other

ridge push

force created by rising mantle of ocean ridges that creates potential for plates to move away from the ridge

slab pull

force created by sinking of a plate, or slab, that pulls on the rest of the plate

subduction

sinking of a denser plate below a more buoyant plate at a convergent plate boundary

asthenosphere

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

rift valley

A deep valley that forms where two plates move apart

basal drag

when convection currents in the asthenosphere drag the lithosphere

plates

slabs of crust and upper mantle