Chapter 9.1 Continental Drift

An Idea Before Its Time Alfred Wegener came up with the hypothesis of continental drift. It stated that the continents had once been joined to from a single supercontinent called Pangaea. He stated that 200 million years ago this continent broke apart and the new smaller continents moved to their current locations.

Evidence: The Continental Puzzle Wegener used the coastlines of the continents to state that they used to fit together like a puzzle.

Evidence: Matching Fossils Fossil evidence is that several fossil organisms were found on different landmasses. Wegener felt these organisms could not have crossed the ocean so they were separated when the continents separated. At one point the though of land bridges joining fossils was accepted but there are no signs that land bridges ever existed.

Evidence: Rock Types and Structures If Pangaea existed then the rocks and mountain ranges on one continent must match the other that it had been connected to. There are several mountain belts that end at one coastline, and reappear on a landmass across the ocean.

Evidence: Ancient Climates Wegener found that much of the world was once covered in ice, especially the southern hemisphere shows signs of glaciation. He used the climate weather to help him place where Pangaea was located.

Rejecting a Hypothesis Wegener got a lot of backlash for his hypothesis. One criticism was how could the landmasses move. Wegener said they moved because of strong tides. Because of his lack of evidence many scientists rejected Wegener’s hypothesis.

A New Theory Emerges Plate tectonic was thought of in the late 1960’s. It was looked at because of earthquake activity.