The theory that states that piecesof Earth’s lithosphere are inconstant, slow motion, driven byconvection currents in the mantle.
• The theory of platetectonics explains theformation, movement,and subduction ofEarth’s plates.
Forces that causes Earth’s plates to move.• The plates of the lithospherefloat on top of the Asthenosphere.• Convection currents rise in theAsthenosphere and spread outbeneath the lithosphere.
Forces that causes Earth’s plates to move (continued).•Convection current forces drag theoverlying plates along. The currents cooland sink deeper into the mantle.• Scientist think that the downwardmovement may provide the force thatcauses the subduction of plates carryingoceanic crust.
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Slab Push Hypothesis• Magma rising along the mid oceanicridge exerts a force that pushes an oceanicplate away from the ridge.• The force of gravity causes platemovement by pulling cooler, denseroceanic plates down toward the mantle.• Slab push and pull work together withconvection currents to move the plates.
The earth’s surface is madeup of about nine large plates & several smaller plates.
• When a divergent boundarydevelops on land, two ofEarth’s plates slide apart.• A rift valley forms along thedivergent valley.• Ex. The Great Rift Valley ineast Africa is about 3,000kilometers long.