Section 3 pages 136- 140 Drifting Continents

1. Section 3 pages 136- 140 Drifting Continents 21. Alfred Wegener theorized that the continents were once all together and have since drifted apart. 22. This idea he called Continental Drift. 23. He believed that about 300 million years ago all the landmasses were together in one super continent called Pangaea.

2. Evidence In Support of Wegener’s Idea 24. There is evidence in land features, fossils, and evidence of climate change to support Wegener’s hypothesis. 25. Land Features- Mountain ranges line up and continents seem to fit together.

3. Evidence Continued 26. Fossil evidence- The fossils of the same plants and animals appear on different continents now separated by oceans.

4. Wegener also presented some fossil evidence. One was an animal fossil and the other was a plant fossil. Mesosaurus was an aquatic dinosaur closely related to the modern Alligator. Its fossil remains are only found near the eastern side of South America and the adjoining western side of Africa when the two continents are positioned side by side. Hence, Wegener concluded that the best explanation for this unusual occurrence is that the two continents were once joined together (or the same landmass), before Mesosuarus became extinct, until they fractured and drifted away from each other.Opposing scientists arguedthat there must have been a land bridgelinking South America and Africa. But no such evidence for a land bridge across the south Atlantic Ocean has been observed since.

5. Evidence Continued 27. Climate – As a continent moves toward the poles its climate becomes colder. As a continent moves towards the equator its climate becomes warmer. The continent will bring with it fossils from its previous location. Example: Fossils from tropical plants have been found on an island in the Artic Ocean. This island must have been originally located near the equator. There is also evidence of glaciers on the continent of Africa indicating it was much colder there in the past. .

7. Wegener’s Theory Rejected 28. At the time Wegener could not show evidence of how the continents moved, so his theory was rejected. The scientist at he time believed that mountains formed from the cooling of the Earth. Wegener said that if that was true then there would be mountains all over the Earth. Wegener proposed that mountains formed from the collision of continents. We now know that the continents move by means of convection currents in the mantle.