divergent		The soft layer of the mantle on which the lithosphere floats.
crust		_____ drift - The hypothesis that the continents drift slowly across the Earth's surface.
pangea		The process by which molten material adds new oceanic crust to the ocean floor.
midoceanridge		_____ boundary - A plate boundary where two plates move away from each other.
convergent		A deep valley where two plates move apart.
wegener		A break in the Earth's crust where masses of rock slip past each other.
riftvalley		The layer of rock that forms Earth's outer surface.
mantle		The force exerted on a surface divided by the area over which the force is exerted.
plate		A dark, dense igneous rock with a fine texture, found in oceanic crust.
deepoceantrench		Vibrations that travel through the Earth carrying the energy released during an earthquake.
granite		A section of lithosphere that carries pieces of continental and oceanic crust.
fault		He formulated the theory of continental drift.
continental		A rigid layer made up of the uppermost part of the mantle and the crust.
lithosphere		The name of the single landmass that broke apart 200 million years ago and became the continents.
transform		The theory that pieces of Earth's lithosphere are in constant motion driven by the convection currents in the mantle.
pressure		Remains of an ancient plant or animal.
seafloorspreading		Dense sphere of solid iron and nickel at the center of the Earth.
fossil		_____ boundary - a plate boundary where two plates move past each other in opposite directions.
platetectonics		Light-colored igneous rock found in continental crust.
core		____ boundary - a plate boundary where two plates move toward each other.
basalt		A deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.
asthenosphere		An undersea mountain chain where new ocean floor is produced.
sonar		A device that determines the distance of an object under water by recording echoes of sound waves.
seismicwaves		Layer of hot, solid material between Earth's crust and core.