1. Continental Drift Alfred Wegener (1880-1930)

2. Alfred Wegener • German meteorologist and geophysicist • Theorized that all the present continents were once part of a super-continent – “Pangaea” • Formed 300 mya • Split apart 200 mya

4. 1. Continental Fit

5. 2. Similarities of Rock Sequences and Mountain Ranges

6. 3. Fossil Evidence

7. 4. Glacial Evidence

8. Theory Rejected • People at Wegener’s time did not accept this theory because he did not know what caused the plates to move • It wasn’t until the 1950 that scientific advances lent more support to the theory of “Continental Drift”

9. The New Discoveries • Ocean floor mapping • Conducted by the US in the 1950s • Accurate mapping of a continuous chain of ridges, 75 000 km long, under the world’s oceans • Mid-Atlantic Ridge – almost exactly midway between the Americas & Europe and Africa • It was concluded that the ridge was where the continents were moving apart • Study conducted by the Glomar Challenger 1968 dated rocks around the ridge • The closer to the ridge the younger the rocks • There are no rocks in the oceanic crust that are greater than 150 million years old

10. Underwater mapping showed that the continental shelves fit more closely together than previously thought • Much closer than the continents themselves fit • This was Wegener’s idea • Seismological records (1950s and 1960s) • Earthquakes are concentrated in a much smaller areas than formerly suspected • Mainly along deep ocean trenches, the ocean ridges, and at other points of contact between the plates of the earth’s crust • Earth magnetism (1950s) • In North America the magnetic “needles” pointed to a different magnetic-pole location than the needles in rocks of the same age in Europe