2.3 theory of plate tectonics
TRANSCRIPT
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The Theory of Plate Tectonics
• Is a theory of why and how the continents move.
• The cold, hard, rigid, outer shell of the earth consist of two types of crust. –Oceanic Crust
• Material on the ocean floor
–Continental Crust• Crust that makes up land masses
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Plates
• Continental Crust–Is more buoyant and not as dense as oceanic
crust. It is comprised mainly of granitic rock.
• Oceanic Crust–Is denser than continental crust because it is
crushed by the massive weight of water that is on it. It is mainly comprised of basaltic and sedimentary rock.
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The Theory of Plate Tectonics
• The oceanic and continental crust make up the lithosphere.–Thin outer shell of the earth
• Below the lithosphere lies the asthenosphere, a layer of molten rock, that is melted and flows (like putty) under pressure.
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The Theory of Plate Tectonics
• According to the theory, the lithosphere is broken into plates that ride (or float) on the asthenosphere.–Like blocks of wood floating on water.
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Lithospheric Plate Boundaries
• Some plates move toward each other, others are moving apart, and some are simply sliding past one another.
• This constant movement is what has created our earth’s major surface.–Mountain Ranges–Deep-ocean Trenches
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Karaoke Moment
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Practice...The wheels on the bus go
round and roundround and roundround and round,
The wheels on the bus go round and round
all through the town.
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Convection Cells
The mantle of the earthGoes round and round,Round and roundRound and round,
The mantle of the earth Goes round and roundAll underground
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Spreading CentersThe convection cells formSpreading centers Spreading centersSpreading centers,
The convection cells formSpreading centersCreating rift valleys
Rift Valley
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Subduction ZonesWhen plates come together One slides down, One slides down,One slides down.
When plates come together One slides
down,We call it a subduction
zone.
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Transform FaultPlates slide past each other at transform faultsTransform faultsTransform faults,
Plates slide past each other at transform faultsand we live next to one!
San Andreas Fault
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Divergent Boundaries• Plates are moving apart from each other
• We also term these sites spreading centers.
• Form what is known as a rift valley.
It is at divergent plate boundaries where new crust is created.
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Convergent Boundaries
• Plates are pushing into neighboring plates.
• Usually a subduction zone occurs. That is when oceanic crust crashes into and slides under continental crust.
• 3 convergent boundaries can occur:–continental/oceanic crust collision–oceanic/oceanic collision–continental/continental collision
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Transform Boundaries
• Formed when two plates grind past each other.
• Example:–San Andreas Fault
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Causes of Plate Motion
• Many scientist believe that the movement of plates is do to convection cells, movement caused by hot and cooler spots in the mantle. So, the mantle is churning.
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Microplate Terrains Theory
–Each terrain has 3 characteristics • Rocks and fossils unique to it’s terrain• Major fault at every boundary• Different magnetic properties