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Plate Tectonics

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

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  1. Plate Tectonics Earth Science Ch. 17

  2. 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"

  3. Plates

  4. 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)

  5. Alfred Wegener • German scientist who proposed “continental drift.” • Named his supercontinent • Pangaea

  6. Pangaea Fig. 17-1

  7. How do the continents drift? • http://videos.howstuffworks.com/hsw/21687-plate-tectonics-volcanoes-and-earthquakes-video.htm • Sea-floor spreading

  8. 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

  9. Ocean floor

  10. Age of ocean sediments • Youngest rocks-closer to ridges • New crust forms at ridges • Oldest are farther away • Crust is destroyed at trenches

  11. Plate tectonics Fig. 17-13

  12. Plate boundaries • Divergent: move apart • Convergent: push together • Transform: slide past each other

  13. 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

  14. Convergent (come together)Fig. 17-15a,b,c • 3 types-depends on crust types • Ocean-ocean • Ocean-continental • Continental-continental

  15. Ocean-ocean Fig. 17-15a • One ocean plate subducts, or goes underneath the other ocean plate • A trench forms • Crust is destroyed here

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

  17. Continental-continentalFig. 17-15c • Both plates are too buoyant to sink • Forms a mtn range instead • Ex. Himalayas

  18. 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

  19. San Francisco earthquake 1989 - Google Video

  20. Possible causes of plate motions • Mantle convection • Push and pull of the plates (gravity) • The End!

  21. References

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