1. 8. 2 Continents change position over time

2. Learning Goals Students will: -explain how the continental drift hypothesis was developed. -explain evidence for plate movement that scientists have gathered from observations of the sea floor. -describe how scientists developed the theory of plate tectonics.

3. 3-Minute Warm-Up Draw a diagram showing and labeling Earth’s four layers. Identify the lithosphere and asthenosphere on your diagram.

4. Continents join together and split apart Mapmakers noticed that eastern coast of S. America and western coast of Africa fit together Alfred Wegner –Hypothesized that Earth’s continents were once joined in a single mass –They gradually moved apart –People didn’t believe him at first continental drift—the hypothesis that Earth’s continents move

5. Evidence of Continental Drift Fossils (pg. 271) –Fossils found in S. America and Africa and no where else

6. Climate – Ancient climate zones show tropical plants on Greenland, which is now mostly ice. Rocks with deep ice scratches can be found in South Africa, which is now a warm climate.

7. Geology –Rocks found in today’s continents matched rocks are found in different areas and different continents

8. Pangaea and Continental Drift Supercontinent of all continents together was called Pangaea—“all lands” Pangaea—a supercontinent that included all of the landmasses on Earth. Wegener could not explain how it moved, so people rejected his hypothesis

9. Plate Tectonics The theory of plate tectonics explains how plates and their continents move Wegner’s idea was pushed aside, until scientists discovered that tectonic plates move

10. Evidence from the Sea Floor mid-ocean ridges—a long line of sea-floor mountains where new ocean crust is formed by volcanic activity. (underwater mountain ranges) Sea-floor spreading –Ridges form along cracks in the crust –Molten rock rises from these cracks –As the sea floor spreads (pulls apart) the old crust is pulled away, making room for new material http://emvc.geol.ucsb.edu/3_downloads/M1GTect/eSoAtlCutGlobeMovi es/SoAtlantic_CutGlobe.movhttp://emvc.geol.ucsb.edu/3_downloads/M1GTect/eSoAtlCutGlobeMovi es/SoAtlantic_CutGlobe.mov http://emvc.geol.ucsb.edu/3_downloads/M3RegTect/bNoCentAtlantic/N oCent_Atlantic.movhttp://emvc.geol.ucsb.edu/3_downloads/M3RegTect/bNoCentAtlantic/N oCent_Atlantic.mov

11. Age of the sea floor –Scientists discovered that the rocks that were further from the ridge were older, so this was evidence of sea-floor spreading http://emvc.geol.ucsb.edu/3_downloads/M3RegTect/aSoAtlanti c/SoAtlanticY.movhttp://emvc.geol.ucsb.edu/3_downloads/M3RegTect/aSoAtlanti c/SoAtlanticY.mov

12. Ocean trenches –Because the sea floor was spreading and increasing, scientists wondering why the Earth did not grow –Reason it did not grow is because there are places where denser oceanic crust is sinking into the asthenosphere http://emvc.geol.ucsb.edu/3_downloads/M3RegTect/dNoPacific/NoPPacific.mov http://emvc.geol.ucsb.edu/3_downloads/M1GTect/eSoAtlCutGlobeMovies/SoAtlantic_ CutGlobe.movhttp://emvc.geol.ucsb.edu/3_downloads/M1GTect/eSoAtlCutGlobeMovies/SoAtlantic_ CutGlobe.mov

13. Causes of Plate Movement Tectonic plates rest on the asthenosphere (layer of soft, hot rock) Convection currents within Earth helps to move the plates convection—the transfer of heat by the movement of a material convection current—a motion that transfers heat energy to a material Moves very slowly, a few centimeters a year Push and pull motion

15. Putting the theory together theory of plate tectonics—the theory that states that Earth’s lithosphere is made up of huge plates that move over the surface of Earth. Scientists combine their knowledge of Earth’s plates, sea floor spreading and the asthenosphere to create the theory of plate tectonics Plates can move apart, push together, or scrape past each other Plate movements cause great change— earthquake, volcanoes, and mountains appear where tectonic plates meet

16. Earth’s tectonic plates. Arrows indicate the direction of movement.

18. http://emvc.geol.ucsb.edu/3_downlo ads/M1GTect/aPangaeaMovies/Pang aea.movhttp://emvc.geol.ucsb.edu/3_downlo ads/M1GTect/aPangaeaMovies/Pang aea.mov

19. Questions What evidence did Alfred Wegner use to hypothesize his theory of continental drift? What does Pangaea mean? What is evidence that the sea floor is spreading? Why doesn’t the Earth grow because of sea floor spreading? In what ways do plates move?