Topic 16: DRIFTING CONTINENTS As early as 1620 Francis Bacon noted the similarity of the east coast of South America and west coast of Africa. In 1858 Antonio Snider showed on maps that Africa and South America might have been joined and broke apart. Wegener's Hypothesis - In the early 1900s Alfred Wegener suggested that continents could fit together to form a giant supercontinent called Pangaea. The northern half of Pangaea is called Laurasia and the southern half called Gondwanaland. According to Wegener's hypothesis Pangaea was disrupted during the Mesozoic Era, and its pieces which are the continents we know today, moved to their present position by some mysterious process called continental drift. Evidence for Pangaea - The following are a number of reasons why Wegener was able to propose existence of continental drift. First, the shape of some continents match, particularly South America and Africa. Second, Wegener noted that plant fossils of late Paleozoic age found on several different continents were quite similar, suggesting that they evolved together on a single large land mass. Third, broad belts of rocks in Africa and South America are the same. These broad belts are match when the end of the continents are joined. Fourth, Wegener was also aware that a continental ice sheet covered parts of South America, southern Africa, India, and southern Australia about 300 million years ago. Glacial striations on rocks show that glaciers moved from Africa toward the Atlantic Ocean and from the Atlantic Ocean onto South America. Such glaciation is most likely if the Atlantic Ocean was missing and the continents joined. Fifth, if the continents were cold enough so that ice covered the southern continents, why is no evidence found for ice in the northern continents? Simple! the present northern continents were at the equator at 300 million years ago as indicated by deposits of coral reefs and deserts. Despite the evidence for continental drift many geologists were uncertain that the hypothesis was valid. New evidence for continental drift came from study of the magnetic properties of rocks during the 1950s.