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.
QuickTime™ and a decompressorare needed to see this picture.
Forces that causes Earth’s plates to move.
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 transform boundary.
The SanAndreasfault inCalifornia isan exampleof atransformboundary.
Two plates move away fromeach other.
• 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.
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
This can happen where oceanic crust meets oceanic crust.
This can happen where oceanic crust meets continental crust.
This can happen where continental crust meets continental crust.
Plate Movement• The plates move at about 1-10centimeters per year.• The North American andEurasian plates move at about 2.5cm/year.
Plate Movement• Pangaea existed about260 million years ago.• Approximately 225million years ago Pangaeabegan to break apart.