1. CONTINENTAL DRIFT Alfred Wegener (1915) introduces CONTINENTAL DRIFT HYPOTHESIS. Super-continent Pangaea separated 200 million years ago. Evidence:  Fit of the continents  Continuity of mountain belts  Glaciation  Fossil evidence  Diversity of species USGS

2. 225 Million Years Ago USGS

3. PANGAEA SUPER-CONTINENT 180 million years ago

4. 135 million years ago

5. 65 million years ago

6. Our world today

7. GLACIAL EVIDENCE matching glacial deposits found on different continents Matching glacial striations (grooves) on different continents

8. FOSSIL EVIDENCE

9. ROCK EVIDENCE alignment of continental shelves Matching of unique rock types across continents

10. MOUNTAIN BELTS EVIDENCE Ranges with the same ages of deformation on opposite sides of ocean Appalachians (N. America) line up with Caledonides (Britain & Scandanavia)

11. Wegener’s Hypothesis Rejected Continental Drift Hypothesis was rejected because Wegener had no working driving mechanism for continental movement Wegener had no working driving mechanism for continental movement

12. Continental Drift Hypothesis turns into Plate Tectonic Theory

13. Plate Tectonic Theory Evidence  Ocean floor was mapped  Earthquake & volcano distribution determined  Paleomagnetism discovered  Age of the ocean floor determined  Hot Spots discovered  And more...

14. EVIDENCE: Mapping of the ocean floor Began in the 1950’s and led to the discovery of:  Deep ocean trenches  Submerged volcanic island chains  Extensive mountain systems on the ocean floor USGS

15. Deep Sea Trenches & Ridges Pearson Prentice Hall

16. EVIDENCE: World wide distribution of earthquakes and volcanoes

17. EVIDENCE: Paleomagnetism  Earth acts like a magnet  Normal polarity: north = magnetic pole  Reverse polarity: south = magnetic pole

18. Paleomagnetism  Magnetometers recorded strange strips on ocean floor  Stripes represented flips in Earth’s polarity  Stripes symmetrical across ridges

19. Paleomagnetism Cooling magma records polarity

20. EVIDENCE: Age of Ocean Rocks