1. Plate Tectonics

2. lithosphere asthenosphere mesosphere

3. Lithosphere (hard) Asthenosphere (soft) Mesosphere

4. Earth formed 4.6 bya • Inner Core- 4300oC • mostly iron core • inner part is so compressed that it is solid • Outer Core- 3700oC • iron and sulfur • liquid • Crust • floats on top of lithosphere • continental crust (granite) • 20 to 70 km thick • oceanic crust (basalt) • ~ 8 km thick • Mantle- 1000oC • mesosphere • Solid • ~ 2300 km thick • asthenosphere • Soft • ~3000 km thick • lithosphere • hard • ~100 km thick

5. Principles of plate tectonics • The Earth is composed of a mosaic of thin rigid plates (pieces of lithosphere) that move horizontally with respect to one another • Plates interact with each other along their plate boundaries • Plate boundaries associated with tectonic activity (mountain building, earthquakes, active volcanoes)

6. Continental Drift Theory Alfred Wegener • Proposed Theory of Continental Drift (1915) • Failed to provide a mechanism

7. Evidence for Continental Drift • continental shape • similar geology • fossil evidence (animal and plant) • volcano and earthquake zone • paleomagnetism

9. Objections to the continental drift model • Wegener envisioned continents plowing through ocean basins • Wegener did not provide a plausible mechanism to explain how the continents could have drifted apart • Most Earth scientists rejected continental drift because it was • Too far-fetched • Contrary to the laws of physics Lacked technology

10. Jigsaw Puzzle Evidence for continental drift • Matching coastlines on different continents

11. Similar Geology Evidence for continental drift • Matching mountain ranges across oceans Today 300 million years ago

12. Evidence for continental drift • Glacial ages and climate evidence

13. Fossil Evidence

14. Fossil Evidence Distribution of fossils such as Mesosaurus Mesosaurus

15. Permian 225 mya Triassic 200 mya Jurassic 135 mya Cretaceous 65 mya Present Day

16. Marie Tharp

17. Marie Tharp's "World Ocean Floor Map” 1977

18. Evidence for plate tectonics • Pattern of worldwide earthquakes (left) matches plate boundaries (right)

19. Plate Tectonics &

20. Hess- Convection Cell Theory

22. The 3 types of plate boundaries • Divergent • Convergent • Transform

23. Divergent plate boundaries • The Mid-Atlantic Ridge is a divergent plate boundary where sea floor spreading occurs

24. Divergent plate boundaries • Iceland sits atop a divergent plate boundary where continental rifting occurs

25. Divergent plate boundaries • Formation of an ocean basin by rifting and sea floor spreading

26. Convergent plate boundaries a. Ocean-continent • Convergent plate boundaries vary depending on the type of crust c. Continent-continent b. Ocean-ocean

27. Convergent plate boundaries • An ocean-continent convergent plate boundary produces the Cascadia subduction zone and Cascade Mountains

28. Convergent plate boundaries • A continent-continent convergent plate boundary produces the Himalaya Mountains

29. Transform plate boundaries • Transform plate boundaries occur between segments of the mid-ocean ridge • Can also occur on land (ex: San Andreas Fault)

30. The world as it may look 50 million years in the future

31. Glomar Challenger (1960’s) Deep sea ocean drilling

32. N S Earth's Magnetic Field

33. Mid-Ocean Ridge (Atlantic Ocean) + - + - + - + - + - + - There have been 170 reversal in the last 76 million years. The earth’s present orientation has existed for the past 60,000 years.

34. Age of the Atlantic

35. Inquiry • What layer of the mantle do the plates move on? • What is the convection cell theory? • Wegeners evidence for continental drift includes: ______. • Why was his theory disregarded? • What did Marie Tharp discover? • How are trenches formed?