The idea that continents move horizontally. Once considered pseudoscientific, this tenet is now part of mainstream science. Before the modern revolution of plate tectonics of the 1950s and 1960s, the idea that the continents might move horizontally around the globe seemed ludicrous; yet prima facie evidence had long been known, in the approximate match between the adjacent coasts of Africa and South America. A very full case for continental drift was made in the early 20th century by the German glacial meteorologist and geologist Alfred Lothar Wegener. He assembled much of the modern evidence, in particular the same fossils and rock strata on the matching coasts of Africa and South America, which was so important for later scientific acceptance. His arguments were discussed most fully in the mid-1920s. Most who considered them rejected them as the work of a crank, in part because he did not have a satisfactory theory of the mechanism of the movement of continents. Wegener also totally ignored counterarguments and counterevidence and appeared too willing to interpret ambiguous evidence favorably.
In the 1950s, improved techniques for measuring Earth’s magnetism gave some disturbing results: In some periods, Earth’s magnetic poles appeared to be in different places simultaneously. That only made sense if the continents had been located differently and had subsequently drifted. In 1929, M. Matuyama showed that the North and South Poles had changed places from time to time. In the 1960s F. J. Vine and D. H. Matthews showed that there were magnetically reversed stripes on the ocean floor, suggesting that rock was being laid down at a split in the ocean floor, forcing the continents apart. Further evidence proved that Earth’s surface consisted of several plates, some drifting apart, other crashing into each other to form mountain ranges, or to produce earthquakes and volcanoes. In the 1980s very sophisticated measurements of the distance between fixed points on adjacent continents, using lasers, satellites and distant galaxies, confirmed that plates do move relative to each other at about 2 centimeters (roughly 1 inch) a year.