PLATE TECTONICS chapter 7

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PLATE TECTONICSchapter 7
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Interior of Earth

• Core
• Inner
• Solid Fe under pressure
• Outer
• Liquid Fe
• Mantle
• Solid plastic
• Crust
• Solid brittle
• Si, O2

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Plates

• Lithosphere- rigid
• Asthenosphere- rock that flows
• Ocean plate- basalt, dense, thin
• Continental plate- granite, less dense, thick

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What is a plate?
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How do we know what is inside the earth?
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core

• Outer- no S waves liquid
• Magnetic field flip supports liquid outer core
• Overall density based on orbit
• Magnetic field iron

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Mantle

• Tomography- look at how temp. differs
• Volcanoes give us a peek

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Crust

• Directly sample (drill cores)
• Sonograms (sound waves)

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What moves the plates?

• Convection currents

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ALFRED WEGENERFather of Plate Tectonics

• 1880-1930

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• Studied Greenlands weather
• meteorologist

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EVIDENCE FOR CONTINENTAL DRIFT

• Shapes of continents
• Identical fossils separated by oceans
• glacial deposits in tropics
• Mt. ranges with exact geology separated by oceans

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EVIDENCE FOR CONTINENTAL DRIFT

• Shapes of continents

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Same rock layers match across continents
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Ancient climates
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No one believed him- why not?

• Didnt know what moved the plates (still
  questionable)
• Didnt know where the edge of plates were

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• Last photo of Wegner
• Died lost in Greenland- 1930

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NEW EVIDENCE

• Sonar (1960s)- mapped ocean floor
• age of ocean floor is young
• Mirror images of ages on each side of ridges

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More new evidence

• Pattern of earthquakes- outline edges of plates

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Maybe Wegner was right!

• New theory (1968) called
• PLATE TECTONIC THEORY
• Included
• new way plates move
• new ocean evidence

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Plate tectonics explains so much!

• Location of
• Volcanoes
• Earthquakes
• Igneous rocks
• Metamorphic rocks
• Mountains
• Folds and faults

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PLATE BOUNDARIES

• Where plates meet

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DIVERGENT

• Move apart
• rifts
• most under the sea- Mid Ocean Ridge, Red Sea
• some continental- East African rift

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Divergent boundaries
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Fissure eruption
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CONVERGENT BOUNDARIES

• Move together

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Ocean-ocean

• Volcanoes form on ocean floor- create island arcs
  (volcanoes off coast)
• trenches

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Japan
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Ocean-continental (subduction)

• trenches
• composite volcanoes
• Volcanoes form on continent

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Mt. St. Helens
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Continental-continental

• Folded mountains- non-volcanic!

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Himalayas

• Mt. Everest

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TRANSFORM(strike-slip)

• Plates slide past each other
• shallow earthquakes

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San Andreas Fault
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What moves the plates?

• Convection currents

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Who gives a schist?

• Predict earthquake areas
• Source for geothermal energy
• Find areas of mineral resources
• Predict future?

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