On the origin of continents - Works in Progress Magazine

Continental drift is as fundamental to geology as natural selection is to biology. Why did it take us hundreds of years to discover it?

Nothing in geology makes sense except in light of plate tectonics: the idea that mobile plates float on top of a thick layer of molten rock surrounding the Earth’s core, and currents in that rock move continents and the ocean floor. Plate tectonics explains earthquakes, the formation of mountains and deep sea trenches, and the fossilized sea creatures found miles from the ocean. By explaining so much both within and outside its field, plate tectonics stands as a sort of Platonic ideal of what a scientific paradigm can achieve.<br>In other ways, plate tectonics is a very unusual paradigm. It was discovered twice: first intentionally by geologists in Europe and its colonial sphere, and second, accidentally, by North American geophysicists. The two paths offer opposite lessons on the secret of scientific discovery. There is no lone genius who can claim the majority of the credit. The theory went from fringe to total acceptance over the course of ten years, with nary a funeral in sight. And it all came together much later than one would think: around the time of the first moon landing in 1969. This is the story of how two separate groups of scientists near-independently discovered plate tectonics with wildly different approaches, and what this can teach us about paradigm shifts.

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Moving mountains<br>Like many scientific concepts, the idea of mobile continents had been proposed repeatedly. Abraham Ortelius, a sixteenth-century Dutch cartographer, is widely credited as the first person to suggest that the continents had not always been in their current positions. In 1596, he noted the match between the eastern coastline of South America and western coastline of Africa, and proposed that they had been separated by a great flood.<br>But credit for the idea of continental drift is generally given to meteorologist and polar explorer Alfred Wegener. In 1912, he published an article titled ‘Die Entstehung der Kontinente’ (The Origin of Continents) laying out his case. He expanded on his theory with a book in 1915, while serving in the German military’s weather service. Revised editions followed in 1920, 1922, and 1929; the third edition was translated into English and French in 1924, kicking off international discussion.

Wegener (left) with a party member, taken shortly before his death on the Greenland ice sheet in 1930.

Image

Wikimedia Commons.

If he wasn’t the first, why is Wegener credited as the origin of the theory of continental drift? The reason is that he was the first to assemble thorough evidence: not just from geology and cartography, but also geodesy (the shape of the Earth, including magnetic and gravitational shape), paleontology, and modern biology. Wegener was a synthesist who brought together information that specialists had ignored.<br>Wegener’s most famous piece of evidence was that Brazil fit neatly into Africa, just as Ortelius had noted four centuries before. But Wegener went beyond the shape of the coastlines. When fit together, geological formations like the Karoo (in South Africa) and Paraná Basin (in South America), or the Cape Fold Belt (in South Africa) and the Sierra de la Ventana (in Argentina), also lined up, albeit imperfectly.

Second, Wegener pointed to geological evidence that South America, Africa, India, and Australia had all been traversed by glaciers. Yet none of these continents could possibly have hosted glaciers at their current latitudes. Even if the world had been cold enough, there wasn’t enough water in the oceans to support that much ice. These observations would be much easier to explain if the continents had historically been adjacent to each other and closer to a pole.

Third, it was already well known before the time of Wegener’s publications that certain fossils of the same species, both animal and plant, were found on multiple continents, dispersed thousands of miles from each other in unexplainable patterns. This finding was previously ascribed to the mysteries of God, but after natural selection had become widely accepted by scientists, it was still an unsolved puzzle.

Further, Wegener noted that coal and fossilized corals are found in modern North America and Europe, even though these continents are too cold to support coral today, and that desert sandstones are found in modern wet environments in Britain, continental Europe, and the northeastern United States. Finally, he pointed to astronomical measurements of Greenland that suggested the island was moving away from Europe at a rate of ten meters per year (a rate later shown to be overestimated by a hundredfold).<br>Putting all this together, Wegener proposed that the continents had drifted apart over time, and that the...