Alfred Wegener and the Theory of Continental Drifting
The theory of continental drifting was first introduced by a German meteorologist and geophysicist named Alfred Wegener in 1915, when he published his book, The Origin of Continents and Oceans. He argued that the continents of Earth were once joined together to form one giant continent, or supercontinent, called Pangaea. As a result of the Moon’s tidal influence, Pangaea began to separate into continents that moved westward to the positions where they are today. This conclusion and several of Wegener’s other findings were opposed and discarded during the theory’s development and especially after his book was translated into several different languages, including English. In order to make his conclusions viable, he had to gather enough evidence (Tarbuck and Lutgens, 2002).
Even though the amount of evidence Wegener collected was exhaustive, he still had one major obstacle that he could not overcome alone. He was unable to provide a believable mechanism explaining how the continents moved. He could only give evidence proving that the continents were once joined together at one period in time. After his death in 1930, his theory of continental drifting would be laid aside for about 20 years. Through the study of paleomagnetism, scientists finally began to see the relevance of Wegener’s findings.
In his studies, he primarily noted the “jigsaw fit of the continents” on opposite coastlines of the Atlantic Ocean. This consideration was what first indicated to Wegener that the continents might have originally been joined together. Even though his observation was very unrefined, later developments in studying the continental shelf by Sir Edward Bullard and his associates in the 1960’s showed that the continents of South America and Africa fit together almost perfectly at a 900-meter depth (Tarbuck and Lutgens, 2002).
Another area of evidence that he gathered was that of fossil evidence. In his studies, “Wegener cited documented cases of several fossil organisms that had been found on different landmasses but which could not have crossed the vast oceans presently separating the continents” (Tarbuck and Lutgens, 2002). One of his major examples is the Mesosaurus, a reptile whose remains were only found in eastern South America and southern Africa. Wegener concluded that since this reptile’s fossils were not found in different, more diverse areas, then the two continents surely were connected in the past.
But what was the mechanism responsible for the movement of such large landmasses? Wegener attributed this to the “tidal attraction of the sun and the moon.” He believed that this attraction affected the earth as well as the ocean. Wegener relied on the fact that tidal movements caused friction within the earth causing a deceleration of its rotational speed, therefore dragging the crust westward. Perhaps the biggest gap in Wegener’s argument was that of how the continents actually moved despite all the evidence he used to prove they were once joined. Since “the tidal force acting on the crust is extremely small,” this drifting mechanism was not considered, and “most geophysicists then turned away from Wegener’s theory” (Takeuchi and others, 1970). One of Wegener’s major opponents was Harold Jeffreys, who also believed in the contraction of the Earth. In answer to Wegener’s proposed drifting mechanisms, Jeffreys rightly suggested that “tidal friction of the magnitude needed to displace the continents would bring Earth’s rotation to a halt in a matter of a few years” (Tarbuck and Rutgens, 2002).
Before the idea of continental drifting was accepted, a geologist named Eduard Suess developed his theory of terrestrial contraction in the late 1800’s and early 1900’s. His theory stated that mountain building occurred as a result of the Earth shrinking in size, and, as a result, the Earth’s skin formed wrinkles just as a “desiccating apple” to “accommodate the diminishing surface area.” The wrinkles that form on the Earth’s surface are made into mountains. He believed that a continuous continental crust initially covered the whole earth. As the earth contracted, he explained, parts of the crust collapsed and became ocean. This process occurred over and over in a continuous cycle changing the ocean to land and the land to ocean (Oreskes, 1999).
The study of paleomagnetism, or fossil magnetism, revived interest in continental drift after a brief gap after Alfred Wegener’s death in 1930 until the early 1950s. Iron-rich minerals that cool off after a lava flow are magnetized once they reach a certain temperature. At this point, they cool off pointing at the currently existing magnetic lines of force. Unless the rock is moved, these minerals will stay pointing in this position retaining its “original alignment.” Now they record the history of the magnetic poles, and they can also reveal the latitude in which they were originally formed. S. K. Runcorn and his associates unexpectedly discovered that the magnetic alignments of the iron-rich minerals in lava flows of different ages varied greatly. This meant either one of two things: the magnetic poles migrated or the continents drifted. Scientists have since come to the conclusion that “if the magnetic poles remain stationary, their apparent movement is produced by the drifting of the continents” (Tarbuck and Lutgens, 2002). Finally, many years after his death, other scientists finally began to believe in Alfred Wegener’s unbelievable idea of continental drifting.