In the 1950s, a number of geologists were trying to make some sense of how Earth's magnetic field works. One of these men was Stanley Runcorn, a geophysicist at the University of Newcastle in England at the time. While measuring the remnant magnetism found frozen into igneous rocks around Europe, he discovered something very strange: It appeared that the position of the north magnetic pole of Earth moved around over time. This was very unexpected. Based on the shape of Earth's magnetic field and the accepted theory of what produced it, the magnetic poles should stay fairly close to the geographic poles. However, according to Runcorn's data, the rocks showed that the north magnetic pole had started out in the Pacific Ocean near Hawaii, then moved over by Japan, and eventually came to rest in its present position in the Arctic.
Of course, there was another possibility. Perhaps the north magnetic pole had stayed in one place while the rocks that he was using to measure the magnetism had moved. Runcorn started looking at the paleomagnetic data from other continents and found that these also showed that the magnetic poles had "wandered" in the past. The problem was that the polar wandering curves from each of the continents showed that the north magnetic pole had been in different places at the same time in the past. This was impossible. If the magnetic pole had in fact moved, then all of the different curves should have pointed in the same direction. They did not. The only explanation that made sense to Runcorn was that continental drift had moved the rocks into different locations while the pole stayed still.
To test this idea, Runcorn made a map of Pangaea similar to the one that Wegener had drawn 40 years earlier. He then plotted the position of the magnetic poles at different times in the past and, sure enough, when the continents were reassembled, the polar wandering curves matched.
When Runcorn published the results, many scientists thought that his data was flawed. They claimed that because the devices used to measure magnetism in rocks were still very crude, what he thought was a moving pole might just have been an error in the readings. Runcorn pressed on, and as the equipment became better, the data showed that he was on the right track. The final clincher came just a few years later when another group of scientists would use reversals in Earth's magnetic field to prove that the oceans were spreading.
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