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Alfred Wegener’s Continental Drift Hypothesis In 1915, Alfred Wegener (1880-1930) published his hypothesis of continental drift in his book The Origin of the Continents and Oceans.

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Alfred Wegener’s Continental Drift Hypothesis
In 1915, Alfred Wegener (1880-1930) published his hypothesis of continental drift in his book The Origin of the Continents and Oceans. He was not the first to observe that certain continental coastlines fit together like pieces of a puzzle, but Wegener drew on a broader range of disciplines, such as geology, oceanography, and paleontology, than earlier supporters of the idea had. This attracted widespread attention and led to robust debate among scientists.

The continental drift hypothesis proposed that Earth’s continents had once been connected but had moved slowly apart and across Earth’s surface over millions of years. Basing his argument on the matching coastlines of continents and the similarity of fossil and rock types on continents separated by oceans, Wegener wrote the following:

The concept of continental drift first came to me as far back as 1910, when considering the map of the world, under the direct impression produced by the congruence of the coastlines on either side of the Atlantic. At first I did not pay attention to the idea because I regarded it as improbable. In 1911, I came quite accidentally upon a report in which I learned of paleontological evidence for a former land bridge between Brazil and Africa. As a result I undertook a cursory examination of relevant research in the fields of geology and paleontology, and this provided immediately such weighty collaboration that a conviction of the fundamental soundness of the idea took root in my mind. The basic “obvious” supposition that the relative position of the continents has never altered must be wrong. The continents must have shifted. South America must have lain alongside Africa and formed a unified block which was split in two; the two parts must then have become increasingly separated over a period of millions of years.

Source

Modified from Alfred Wegener, The Origin of the Continents and Oceans, 4th ed., trans. John Biram (New York: Dover Publications, 1966) 1, 17.

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When Wegener proposed his continental drift hypothesis, he knew that similar fossil remains had been found on different continents. This diagram illustrates this point.

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Response to Wegener’s Hypothesis
Most scientists found serious flaws in Wegener’s hypothesis, and many dismissed it outright. One major weakness was that Wegener failed to provide a mechanism, or an explanation, for how the continents moved. Still, some scientists thought that the continental drift hypothesis could be very important and needed to be explored further. These passages represent some of the discussions scientists had about Wegener’s hypothesis.

From G.W. Lamplugh:

It may seem surprising that we should seriously discuss a theory which is so vulnerable. Yet Wegener’s hypothesis is of real interest to geologists, because it has struck an idea that has been floating in their minds for a long time. The underlying idea that the continents may not be fixed has in its favor certain facts which give every geologist a [liking] towards it in spite of Wegener’s failure to prove it. We are discussing his hypothesis seriously because we should like him to be right, and yet I am afraid we have to conclude that in essential points he is wrong. But the underlying idea may yet bear better fruit.
From Mr. F. Debenham:

I believe we are all ready to be kind to the germ of the theory. In fact, most people are rather anxious that something of the sort should be proved. We have to thank Professor Wegener for a great deal in bringing it forward and offering himself as a target for bullets. Not for the first time perhaps, but for the first time boldly, Wegener has come forward with a theory which deals with the distribution of the continents in a bold way and offers himself for sacrifice; and he is certainly getting it.

Source

Modified from G. W. Lamplugh, R. D. Oldham, F. Debenham, Harold Jeffreys, Dr. Evans, and C. S. Wright, “Wegener’s Hypothesis of Continental Drift: Discussion.” The Geographical Journal 61:3 (1923): 188-94.

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More Evidence of Continental Drift: Seafloor Spreading
Following the initial controversy over Wegener’s continental drift hypothesis, there was little written about it for several decades. In the 1950s, the newly developed field of paleomagnetism (the study of Earth’s magnetic field) proved that the continents had once been positioned differently by uncovering certain minerals known to form in alignment with Earth’s polarity that pointed in easterly or westerly directions instead of north or south. But until an adequate mechanism to move the continents was found, many scientists remained unconvinced. Then, in 1959, a U.S. Navy officer and Princeton geology professor named Harry Hess (1906-1969), who had used sonar during World War II to map vast areas of the Pacific bottom, wrote a paper explaining a process he called seafloor spreading: molten rock seeps up from the Earth’s interior through mid-ocean ridges (undersea mountain chains), spreads out to create new ocean floor, and then sinks back into the Earth’s interior through oceanic trenches. This would prove to be the mechanism for continental drift that scientists had been longing for.

Seafloor SpreadingView LargerView Larger
The figure above illustrates Hess’ model of seafloor spreading. New ocean floor is formed by volcanic magma spewing through mid-ocean ridges. Older ocean floor is forced away from the ridge until it is finally pushed below continental plates at ocean trenches. New ocean floor created at ridges moves continents away from one another; the sinking of ocean floor into trenches (a process called subduction) moves continents toward one another. Seafloor spreading made continental drift a plausible idea.

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Importance of the Vine-Matthews-Morley Hypothesis
Like Wegener, Hess initially encountered resistance to his hypothesis because ocean floor data was scarce at the time. This soon changed. Paleomagnetists had determined that Earth’s magnetic field sometimes flips its orientation, on average every 450,000 years. Such a flip, or “reversal,” means that at times in the past a compass needle would have pointed south instead of north. This led geophysicist Fred Vine and geologists Lawrence Morley and Drummond Matthews to propose the Vine-Matthews-Morley hypothesis in 1963: if new oceanic floor is continually being created at mid-ocean ridges, ocean floor rocks should record past reversals of the magnetic field. Subsequent research by geophysicist Walter C. Pitman confirmed the Vine-Matthews-Morley hypothesis. The figure below illustrates their idea.

Magnetism of the SeafloorView LargerView Larger
Walter C. Pitman studied the magnetic orientation of the ocean floor on either side of the Pacific-Antarctic Ridge. The black stripes represent parts of the seafloor that formed when the orientation of Earth’s magnetic field was “normal” (as it is in our times) and the white stripes represent parts of the seafloor that formed when the magnetic field was “reversed.” The pattern confirms the seafloor-spreading hypothesis.

Source

Modified from Vine, F. J., and Matthews, D. H., “Magnetic Anomalies Over Oceanic Ridges.” Nature, (1963),199, 947-949.

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Acceptance of Continental Drift
Confirmation of the Vine-Matthews-Morley hypothesis proved that the seafloor spreads as Hess had claimed. This helped validate Wegener’s continental drift hypothesis. It was also important to the development of the plate tectonics theory, which describes the large-scale motions of the lithosphere. The lithosphere is the Earth’s outermost shell, which consists of the crust and a portion of the underlying mantle. The following passages are from two scholars writing about the continental drift debate. Both of their articles were featured in Nature magazine, the world’s most cited interdisciplinary science journal.

From Henry Frankel:

Plate tectonics provides Earth scientists with a new framework. Because continents are more buoyant than the sea floor, they remain on the Earth’s surface where they move about, collide, break apart, and form new aggregates. Geologists, paleoclimatologists, and biogeographers also quickly exploited the continental drift aspect of plate tectonics. Besides applying continental drift to problems in their specialty, they offered reconstructions and traced geological matches between formerly joined continents. Plate tectonics has shown that the question “How can continents plough through a rigid sea floor?,” the nemesis of continental drift, is not the question to ask. Rather, the key question is “What forces drive the plates?” Unlike continental drift, plate tectonics has not been rejected because the empirical support for plate tectonics provided by confirmation of Vine-Matthews-Morley is so much stronger than what was available for continental drift. Moving plates, like evolving species, have become accepted as fact.
From Fred Vine:

The advent of new and independent evidence suggestive of drift, from paleomagnetic studies, resuscitated the idea in the late fifties and sixties, and subsequently the post-war investment in marine geology and geophysics paid off in the form of providing compelling evidence for seafloor spreading and hence continental drift. By the late 1960s, the vast majority of geologists and geophysicists were convinced that continental drift was a reality.

Sources

Modified from H. Frankel, “From Continental Drift to Plate Tectonics.” Nature 335 (1988): 127-30.
Modified from F. V. Vine, “The Continental Drift Debate.” Nature 266 (1977): 19-22.

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