1. Chapter 7Plate Tectonics

2. Section 7-1 Earth’s Interior The Earth is composed of 4 layers:

3. Video How do we know what’s inside Earth?

4. Earth’s Interior

5. Crust- Earth’s “outer skin” 3-40 miles thick. Made of solid rock. Thickest on continents (continental crust), thinnest below ocean (oceanic crust) Mantle- largest layer, plastic-like and able to flow Outer core- liquid iron and nickel. Inner core- solid iron and nickel because of extreme pressure.

6. History of Plate Tectonics Alfred Wegener- German scientist, believed continents were once joined and moved to present locations. Proposed theory of Continental Drift in 1912. Stated Pangaea broke apart over 200 million years ago.

7. Wegener and Pangaea

8. Evidence of Wegener 1. Puzzle-like fit of continents. South America and Africa look to fit. 2. Fossil Clues- Same fossils found on South America and Africa Mesosaurus- alligator-like fossil Glossopteris- fern- like fossil

9. Evidence Con’t 3. Rock Clues- Similar rock types of same age found in mountains of England and Eastern U.S. 4. Glacial Clues- Evidence of glaciers exist in areas that are too warm for them now Wegener died in 1930, scientific community made a joke of his work.

13. Seafloor Spreading 1960- Harry Hess took Wegener’s work and proposed theory of Seafloor Spreading. Hot, molten material is forced upward and pulls apart the crust. Lava fills in rift to create new seafloor.

14. Seafloor spreading

15. Mid-Atlantic Ridge How do we know seafloor looks like this? Sonar waves, satellites, GPS Mid-Atlantic Ridge discovered during WWII while Navy was mapping ocean floor

16. Evidence for Seafloor Spreading 1. Age of rocks. Glomar Challenger, a seafloor drilling ship sampled rocks along ocean ridge. Rocks get older moving away from the Mid-Atlantic ridge.

17. Evidence Con’t 2. Magnetic Clues- a magnetometer showed that the rocks along the mid-atlantic ridge had a reversal in magnetic polarity.

18. Magnetic evidence

19. Earth’s Magnetic Field Generated by the circulation of the core of the Earth Protects us from harmful rays of the Sun Rocks on seafloor record past events of magnetic reversal.

20. Theory of Plate Tectonics Plate Tectonics-states that Earth’s crust and upper mantle are broken into sections called plates. 12 major plates, move at an average of 1 inch per year. Lithosphere-crust and upper mantle plates are composed of. The lithosphere floats on top of the a plastic-like layer called the Asthenosphere

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22. What causes the Plates to Move? Convection Currents- A heating cycle in the mantle in which mantle material rises and cools

24. Divergent- 2 pieces of continental crust Causes EQ’s, rift valleys, volcanoes Examples are Iceland, Great rift valley, and Red Sea Plate Boundary Types

25. Divergent- 2 pieces of oceanic crust Examples are Mid-Atlantic Ridge,East Pacific Rise. EQ’s and mid-ocean ridges occur

26. Plate Boundaries Convergent- 2 pieces of continental crust Causes Earthquakes, mountain building. Forms the Himalayan Mts.

27. Convergent- 1 piece of continental crust, one piece of oceanic crust Causes Earthquakes, volcanic mountains, trenches Magma generated along subduction Zone. Area where crust melts into mantle. Andes mountains, Mt St. Helens

28. Convergent- 2 pieces of oceanic crust Causes EQ’s, volcanic island arcs, trenches Formed Japan, Philippines, Marianna Trench

29. Transform boundary Causes Earthquakes Formed San Andreas Fault