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The theory that states that piecesof Earth’s lithosphere are inconstant, slow motion, driven byconvection currents in the mantle.
• The theory of plate tectonicsexplains the formation,movement, and subduction ofEarth’s plates.
Forces that causes Earth’s plates to move.• The plates of the lithosphere float on top of the Asthenosphere.• Convection currents rise in the Asthenosphere and spread outbeneath the lithosphere.• Convection current forces drag the overlying plates along. Thecurrents cools and sinks deeper into the mantle.• Scientist think that the downward movement may provide theforce that causes the subduction of plates carrying oceanic crust.
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.
Places where two plates meet.
There are three types of plate boundaries.1. Transform Boundary2. Divergent Boundary3. Convergent Boundary
Two plates slip past eachother, moving in oppositedirections.
Earthquakes occur frequently along this boundary.
The SanAndreasfault inCalifornia isan exampleof atransformboundary.
Two plates move away fromeach other.
• When divergent boundarydevelop on land, two of Earth’splates slide apart.• A rift valley forms along thedivergent valley.• Ex. The Great Rift Valley ineast Africa is about 3,000kilometers long.
Two plates move towards each other.
• When plates converge, it results in a collision. • Collisions happen between:1. Oceanic crust to oceanic crust2. Oceanic crust to continental crust3. Continental crust to continental crust
Plate Movement• The plates move at about 1-10centimeters per year.• The North American and Eurasianplates move at about 2.5 cm/year.
Plate Movement• Pangaea existed about 260 millionyears ago.• Approximately 225 million years agoPangaea began to break apart.