Chapter 8 - Plate Tectonics

1. Chapter 8 - Plate Tectonics http://sos.noaa.gov/datasets/Land/paleo.html Animations On the move…

2. Plate Tectonics: the rocky history of an idea • Ever notice that the shore lines of South America and Africa seem to fit together?

3. Antonio Snider-Pellegrini's Illustration of the closed and opened Atlantic Ocean (1858).

4. Continental Drift: a theory • In 1912, Alfred Wegener proposed the idea of “continental drift.” • The continents were once part of a single land mass and they drifted to their present locations.

5. Continental Drift • Wegener named the supercontinent Pangea (meaning “all lands” in Greek) • The vast ocean that surrounded Pangea was named Panthalassa.

6. Evidence used to support the Continental Drift Theory • The continents shapes match • The plants & animals (fossils) match • The rocks match • The ice matches • The climates don’t match

7. The shorelines of the continents appear to fit together like a jigsaw puzzle.

8. The plant & animal fossils match • Fossils of the same kind were found on several different continents. Ex: Mesosaurus & Glossopteris

9. The rock matches • Rocks of the same age, same types and structure are found on widely separated continents

10. The rock matches • When the continents are reassembled, the mountain chains form a continuous belt. • Ex: The Appalachianand Caledonian mountain ranges align.

11. The ice matches

12. The ice matches

13. The ice matches • Glacial striations on rocks show that glaciers moved across continents Scratches from a glacier.

14. Climate Change This frozen land must have been situated closer to the equator in the past, in a warmer climate where, swampy vegetation could grow. • The discovery of fossils of tropical plants in the form of coal deposits in Antarctica.

15. Climate Change • Glacial till & striations found in deserts. Moraine and till

16. St. Mary Lake, Glacier National Park.

17. Bridal Veil Falls in Yosemite National Park flowing from a hanging valley New Zealand's Franz Joseph glacier

18. Yeager Rock, a 400 ton erratic sitting on top of glacial till on the Waterville Plateau, Washington.

19. Although plenty of evidence supports Wegener’s Continental Drift theory, it was not accepted by the scientific world at the time. Pretend you are a skeptical scientist. • Would Wegener’s evidence be enough to convince you that the continents are moving? • What could you argue against this theory? • What is Wegener missing?

20. The mystery… • How does it work? • What causes the motion? • Do continents just plow through the ocean? These questions weren’t answered until decades later after Wegener’s death.

21. …solved • Beginning in the 1950’s new evidence emerged to support the old theory and helped develop a new one… Plate Tectonics

22. Imagine an Earth without water

23. Plate Tectonics…in general: • The Earth’s solid surface is broken up into pieces called plates that “float” on top of the gooey part of the mantle.

25. Plate Tectonics: a beginning • To understand the relatively new idea of Plate Tectonics, we have to review the layers of the Earth.

26. Crust – 2 types • Ocean crust • Thin, dark in color • More dense • Mostly made of Basalt • Continental crust • Thick, light in color • Less dense • All rock types

27. Inside Earth:

28. Tectonic Plates are made from the Earth’s broken lithosphere. • The lithosphere consists of the crust and the upper solid part of the mantle.

29. The lower pliable part of the mantle is the asthenosphere. • The lithospheric plates move over the slow flowingasthenosphere.

31. New Evidence used to develop Plate Tectonics • Ocean floor mapping led to the discovery of… • Seafloor spreading • Magnetic Reversals • Locations of Earthquakes and Volcanoes

32. Ocean Floor Map

33. Mid-Ocean Ridges • Mid-Ocean Ridges are chains of volcanic mountains on the ocean floor with a deep central valley called a rift zone. Mid-ocean ridges are the sights of Seafloor Spreading.

34. Seafloor Spreading • occurs where oceanic plates are moving apart. Magma rises through the rift and spreads out at the surface building new sea floor.

35. As magma cools & hardens it pushes ocean floor away from the ridge forming new ocean crust. • Old rock is destroyed in a trench.

36. Age of rocks increase away from the rift zone http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm

37. More evidence… • Magnetic reversals recorded in rocks along the mid-ocean ridges support Seafloor Spreading and Plate Tectonics. • The direction of the Earth’s magnetic field are preserved in the new rock formed at the ridges. • The poles switch and are seen in a pattern of bands paralleling mid-ocean ridges. http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm

39. Earthquakes mark plate boundaries

41. Locations of Earthquakes & Volcanoes • Do not occur randomly. • Actually mark the locations of plate boundaries. • Occur when plates are pushing towards, pulling away, or sliding past each other.

42. Remember…convection is the motion of boiling water

43. What drives the plates? Mantle Convection

44. Plate Boundaries…are where two plates meet • 3 types of motions Divergent Convergent Transform Fault http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm

45. Divergent Boundaries • Plates are moving apart and new crust is created. • Land or Ocean crust splits. • A rift valley over land forms when continental crust splits. • A mid-ocean ridge forms when ocean crust splits.

46. Divergent – Continent splits

47. Divergent – Rift Valley • Example: East African Rift Zone

48. Divergent Boundaries • Ex: Mid-Atlantic Ridge & Eastern Pacific Rise

49. Divergent Boundaries

50. Convergent Boundaries • Plates are moving towards each other. • Ocean  Continent • Ocean  Ocean • Continent  Continent