fossil - remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in rock, superposition - layers of rock are dated by oldest on bottom and youngest on top, plate tectonics - theory that explains how the surface of the Earth changes, seafloor spreading - formation of new areas of oceanic crust, density - mass/volume, lithosphere - solid outer crust, asthenosphere - molten upper portion of the mantle, convection currents - circulating currents in the mantle move the plates above, slab pull - subducting slabs are pulled by gravity to the center of the Earth, divergent boundaries - plates separate, rift valleys - large elongated depression with steep walls; Continental - Continental divergent, mid ocean ridges - ridge system situated in the middle of an ocean basin; Oceanic - Oceanic divergent causing ocean basin to widen, convergent boundaries - plates collide; Continental - Continental convergent causes mountains to form, subduction zones - occur when a more dense oceanic plate is forced down into the mantle; Continental - Oceanic convergent; in the ocean they form deep ocean trenches and volcanoes, volcanic island arcs - a belt of volcanoes formed above a subducting oceanic tectonic plate, ocean trenches - long, narrow depressions on the seafloor; deep chasms, transform boundaries - plates pass by each other; area where faults and earthquakes form,

7th gr Changing Earth

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