Plate Tectonics (Continental Drift)

200 million years (m.y.) ago
Continents were assembled in a single supercontinent called Pangeae.

Early evidence for continents once being grouped together:

1. geometric fit of the continents
   • in 1620 Sir Francis Bacon wrote "the geometrical similarity between the western coast of Africa and the eastern coast of South America can hardly be denied".
   • Alfred Wegener
   • Sir Edward Bullard
     • computer fit of the continents using 2000m depth contour
     • much better fit than using present-day shorline
2. Continental Geology
   • rocks in N. America should be the same type and age as those in N.W. Africa
   • if the Americas were joined with Africa 200 m.y. ago, then they should have the same flora (plants) and fauna (animals).
3. Climate
   • look at the geograph distribution of sediment deposited by a glacier. These sediments are called tillites.
   • Coral Reefs - today, coral reefs do not occur where the water temperature falls below 18 C. We find ancient coral reefs at high latitudes. Why? The continents have moved.
     • originally in the tropics and carried to present-day position by movement of the continents