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Plate Tectonics. Earth Science Ch. 17. Plate tectonics. Earth’s crust is “broken” into many plates There are 7 large plates Plates move 1-10 cm per year HowStuffWorks Videos "Continental Drift". Plates. Possible evidence for moving plates. Shape of continents (“fit” together)

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Plate tectonics

Plate Tectonics

Earth Science Ch. 17


Plate tectonics1
Plate tectonics

  • Earth’s crust is “broken” into many plates

  • There are 7 large plates

  • Plates move 1-10 cm per year

  • HowStuffWorks Videos "Continental Drift"



Possible evidence for moving plates
Possible evidence for moving plates

  • Shape of continents (“fit” together)

  • Rock formations-p. 444

  • Fossil evidence: Fig. 17-2

    • Similar fossils found on opposite sides of oceans

  • Ancient climate evidence (coal on antarctica, glacial deposits in africa)


Alfred wegener
Alfred Wegener

  • German scientist who proposed “continental drift.”

  • Named his supercontinent

  • Pangaea



How do the continents drift
How do the continents drift?

  • http://videos.howstuffworks.com/hsw/21687-plate-tectonics-volcanoes-and-earthquakes-video.htm

  • Sea-floor spreading


Sonar fig 17 5
Sonar Fig. 17-5

  • Uses echo-sounding to measure depth of ocean floor

    • Discovered underwater mtn chains

    • And trenches

  • Magnetometer: detects changes in magnetic fields



Age of ocean sediments
Age of ocean sediments

  • Youngest rocks-closer to ridges

  • New crust forms at ridges

  • Oldest are farther away

  • Crust is destroyed at trenches



Plate boundaries
Plate boundaries

  • Divergent: move apart

  • Convergent: push together

  • Transform: slide past each other


Divergent move apart fig 17 14
Divergent (move apart) Fig. 17-14

  • Most found on seafloor, but also the East African Rift Valley

  • Formation of new crust

  • Atlantic Ocean grows about 1” a year


Convergent come together fig 17 15a b c
Convergent (come together)Fig. 17-15a,b,c

  • 3 types-depends on crust types

  • Ocean-ocean

  • Ocean-continental

  • Continental-continental


Ocean ocean fig 17 15a
Ocean-ocean Fig. 17-15a

  • One ocean plate subducts, or goes underneath the other ocean plate

  • A trench forms

  • Crust is destroyed here


Continent ocean fig 17 15b more dense ocean plate sinks
Continent-ocean Fig. 17-15b-more dense ocean plate sinks


Continental continental fig 17 15c
Continental-continentalFig. 17-15c

  • Both plates are too buoyant to sink

  • Forms a mtn range instead

  • Ex. Himalayas


Transform slide past fig 17 17
Transform (slide past) Fig. 17-17

  • Crust is fractured, generally forms faults

  • Most occur in oceans

  • Most famous example is San Andreas Fault in CA



Possible causes of plate motions
Possible causes of plate motions

  • Mantle convection

  • Push and pull of the plates (gravity)

  • The End!



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