1. Continental Drift The Beginning of Plate Tectonics

2. Continental Drift: The Beginning First studied when maps were made in the 1500’s. Alfred Wegener - 1912 credited with first hypothesis of Continental Drift

3. Did they really fit together? Looked at maps saw similarities of coastlines, not a good fit but similar.

4. Need to look off coastline(200 m depth) to continental shelves, better fit. More realistic because these areas were once above sea level and would have been the edge of the continent at one time. Need to look off coastline(200 m depth) to continental shelves, better fit. More realistic because these areas were once above sea level and would have been the edge of the continent at one time.

5. Continental Shelves

6. A Better Fit?

7. Super-continent: Pangaea Called this super- continent-Pangaea- ”all lands” Called ocean formed around it Panthalassa-”all seas”

8. This happened about 200 million years ago, and then Pangaea started to break apart.

9. Evidence 1. Fossils- Mesosaurus-found in Eastern South America and Western Africa couldn’t have swam across the Atlantic Index fossils- have specific habitats, and lived during specific time frame.

10. Fossils

11. 2. Geologic evidence a. Mountain chains -Appalachians follow to Greenland and Northern Europe.

12. b. Geologic rock formations formed under similar conditions.

13. c. Similar climate conditions evidence of glaciers in areas that presently would not support glaciers in Africa and South America.

14. Glacial Striations

15. d. Coal deposits showing warmer climates that today would not support the plant life necessary to form these deposits.

16. ?????????????? Nice evidence Nice evidence A lot of people would not buy this idea on the evidence provided. A lot of people would not buy this idea on the evidence provided. They still wanted more. They still wanted more.

17. Important piece to the puzzle: Sea-Floor Spreading

18. The Key 1947- Mid -Atlantic Ridge (Rift)-under sea mountain range part of 65,000 km long range that goes around the earth. 1947- Mid -Atlantic Ridge (Rift)-under sea mountain range part of 65,000 km long range that goes around the earth. MOR-mid ocean ridge

19. Mid-ocean Ridges

20. Ocean floor rocks only 150 million years old at most

21. Continental rock up to 4 billion years old Minnesota Gneiss (nice)

22. Paleo-magnetism-change in magnetic orientation of rocks along either side of the mid-Atlantic rift zone.

23. Normal Polarity Where the north magnetic pole is as it is today. North magnetic pole is north geologic pole Compass needle points north.

24. Reversed Polarity Where the north magnetic pole is at the south geologic pole (Antarctica) Where the north magnetic pole is at the south geologic pole (Antarctica) Compass needle points to our present south pole. Compass needle points to our present south pole.

25. Polar Reversals

26. Continental Drift Humor