1. Chapter 17 Plate Tectonics

2. Drifting Continents: Early Observations Cartographers were the first people to notice matching continents Antonio Snider-Pelligrini (1858)

3. Alfred Wegener German meteorologist/climatologist 1912: proposed the idea of continental drift –Continents started as “Pangea” 200 million years ago –Slowly moving apart to present positions

4. Evidence for Continental Drift Matching coastlines Matching rock formations/mineral deposits separated by oceans Climate evidence: fossil ferns Glossopteris) found in Antarctica, South America, and India Matching fossils on widely separated continents (Cynognathus, Lystrasaurus, Mesosaurus)

5. Fossil Evidence

6. Flaws of Continental Drift Did not explain the immense forces required to move continents long distances No evidence of continents “plowing through” the ocean crust Continental Drift was rejected until the early 1960s, when these flaws were resolved

7. Seafloor Spreading Technology advances in the 1940s and 1950s led to more detailed ocean floor mapping Magnetometer: detects changes in magnetic fields Sonar: found mid-ocean ridges and deep sea trenches Interesting patterns in age of rock samples

8. Magnetic Patterns and Seafloor Spreading

9. Age of Ocean Crust and Seafloor Spreading

10. Sediment Depth and Seafloor Spreading Evidence for seafloor spreading corrected a flaw of Wegener’s model of continental drift Continents ride along while ocean crust moves away from mid ocean ridges

11. Types of Plate Boundaries: Divergent Plates moving apart Mid-ocean ridge On land: rift valley

12. Types of Plate Boundaries: Convergent Continent-continent Ocean-continent Ocean-ocean

13. Types of Plate Boundaries: Transform Plates slide horizontally past each other

14. What Causes Plates to Move?