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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 Rock of continents (“fit” together) 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 German scientist who proposed “continental drift.” Named his supercontinent Pangaea Pangaea Fig. 17-1 How do the continents drift? http://videos.howstuffworks.com/hs w/21687-plate-tectonics-volcanoesand-earthquakes-video.htm Sea-floor spreading Sonar Fig. 17-5 Uses echo-sounding to measure depth of ocean floor – Discovered underwater mtn chains – And trenches Magnetometer: magnetic fields detects changes in Ocean floor Age of ocean sediments Youngest rockscloser to ridges New crust forms at ridges Oldest are farther away Crust is destroyed at trenches Plate tectonics Fig. 17-13 Plate boundaries Divergent: move apart Convergent: Transform: push together slide past each other Divergent (move apart) Fig. 17-14 Most found on seafloor, but also the East African Rift Valley Formation Atlantic of new crust Ocean grows about 1” a year 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 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 Continental-continental Fig. 17-15c Both plates are too buoyant to sink Forms Ex. a mtn range instead Himalayas Transform (slide past) Fig. 17-17 Crust faults Most Most is fractured, generally forms occur in oceans famous example is San Andreas Fault in CA San Francisco earthquake 1989 Google Video Possible causes of plate motions Mantle Push The convection and pull of the plates (gravity) End! References
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