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42Evolution

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Alfred Wegener

Alfred Wegener. Taken during a 1912-1913 expedition to Greenland (Image: Alfred Wegener Institute via Wikimedia Commons)

Photograph of Alfred Wegener taken during a 1912-1913 expedition to Greenland (Image: Alfred Wegener Institute/Wikimedia Commons)

Alfred Wegener (1880-1930) was a German geophysicist and a pioneer of polar research. He made a lasting contribution to evolutionary studies by developing the theory of ‘continental drift’; the idea that all Earth’s continents had once been joined together and had slowly drifted apart. The idea was largely rejected by geologists when it was first proposed in 1912, but it is now regarded as one of the cornerstone concepts of plate tectonics and is fundamental to our understanding of Earth’s evolution.

To understand the importance of the idea of continental drift, one must first understand the conventional view of the structure of Earth held in the early twentieth century. Most people believed that the continents were ‘static’, an argument set down by the geologist Eduard Suess. Suess claimed that the Earth had been formed in a molten state and as it cooled it had formed an outer ‘crust’. According to this theory, the continents had never moved. One obvious problem to this idea was that there existed numerous examples of the same type of fossil (and indeed living) animal species on separate continents. For example, fossil remains of the small Palaeozoic reptile Mesosaurus, are only found in South America and Africa; landmasses that are today on opposite sides of the Atlantic. Although Mesosaurus was aquatic, it was not an ocean-going reptile, so this and other such occurrences (such as the plant Glossopteris) were accounted for by postulated land bridges – now submerged – which once connected these far-flung areas.

Wegener’s interest was piqued by such examples, but he also noted that geological features on different continents often fit together. For example, the Cape fold belt of South Africa matches the range of Buenos Aires in Argentina, and the early Palaeozoic and late Palaeozoic mountain belts of western Europe form a line of continuation with those in Newfoundland and Nova Scotia.

In 1912, Wegener presented the idea of ‘continental displacement’ in a lecture to the German Geological Association. This would later become known as continental drift. The theory explained how Earth’s continents have moved (and, as importantly, continue to move), and also suggested that mountains were formed as a consequence of one continent colliding with another. For example, the Himalayas were formed as a result of the Indian sub-continent ‘drifting’ into Asia. In 1915, Wegener published his most famous work, Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans).

It wasn’t until the third edition in 1922 that the book was translated into English and this was published in 1924. In this, he proposed that around 300 million years ago, all Earth’s landmass was joined together as one giant continent which had gradually fractured and drifted apart. He called this supercontinent ‘Pangaea’ (meaning ‘all land’). Wegener’s earlier papers rested strongly on geological evidence to support his theory, but this would grow to include equally strong evidence from palaeoclimatology. For example, glacial sediments of Permo-Carboniferous age in Australia, Brazil and South Africa testify to the presence of ice sheets, and supported his suggestion that the southern continents once straddled the southern pole.

Animation demonstrating the break up of the supercontinent Pangaea (Image: U.S. Geological Survey via Wikimedia Commons)

Animation illustrating the break up of the supercontinent Pangaea around 200 million years ago (Image: U.S. Geological Survey/Wikimedia Commons)

Wegener died in 1930, during the extreme conditions of an expedition to Greenland. He received a full page obituary in Nature, which was testimony to, and acknowledgement of, the immense contribution he made to science.

By the end of the 1960s, advances in geophysics and oceanography had provided such compelling support of continental drift, that the idea became almost universally accepted. Prior to that, although to many geologists, especially those working in the Southern Hemisphere, the evidence for continental drift was too obvious to be ignored, the idea first postulated by Wegener slumbered. Why? Effectively, and at that time for good reasons, physicists were adamant that the properties of the interior of the Earth simply made continental drift and what today we call ‘plate tectonics’ an impossibility.

Of course, one needs the best of science of the day, and the information provided by physicists always needs to be taken seriously. Even so, physicists dismissed the possibility of continental drift and this had more than an echo of Lord Kelvin’s pronouncement as to the age of the Earth. But Kelvin’s estimation was based on thermodynamic assumptions of rates of cooling and the calculations could take no account of the heat produced by radioactive decay for the simple reason that radioactivity was yet to be discovered.

The moral of the story is simple but too often ignored: If two (or more) lines of evidence appear to be in utter contradiction do not exclude the possibility that one is based on incomplete data. That way one can move (intellectual) mountains and continents.

Text copyright © 2015 Victoria Ling. All rights reserved.

References
Hallam, A. (1973)  A Revolution in the Earth Sciences: From Continental Drift to Plate Tectonics.  Clarendon.
Hallam, A. (1975)  Alfred Wegener and the hypothesis of continental drift.  Scientific American 232, 88-97.
Modesto, S.P. (2006)  The cranial skeleton of the Early Permian aquatic reptile Mesosaurus tenuidens: implications for relationships and palaeobiology.  Zoological Journal of the Linnean Society 146, 345–368.
Wegener, A. (1912) Die Herausbildung der Grossformen der Erdrinde (Kontinente und Ozeane), auf geophysikalischer Grundlage.  Petermanns Geographische Mitteilungen 63, 185–195, 253–256, 305–309.
Wegener, A. (1915)  Die Entstehung der Kontinente und Ozeane.  Friedrich Vieweg & Sohn.
Yount, L. (2009)  Alfred Wegener: Creator of the Continental Drift Theory.  Chelsea House.

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