Seminar

Whether South America and Africa were ever joined together has been the speculation since Abraham Ortelius made the suggestion in the late 1500s. Alfred Wegener, “the father of continental drift”, believed that all of the major continents had been joined when the coal of Europe and North America was laid down and then had drifted apart in much the same way as ice floes do when the winter turns to spring.

Harold Jeffreys (St John’s College, Cambridge) showed such a mechanism was physically impossible, a result that has incorrectly been taken as a proof that continental drift could not occur. Sam Carey, a Tasmanian, made a very precise visual reconstruction on a globe. It showed the excellence of the fit between edges of the two continents, a result that was computerized in 1963 by Jim Everett, a research student of Teddy Bullard. It was the first application of Euler’s theorem to the problem of how to fit continents together. At about the same time, Fred Vine, while a research student in St. John’s, supervised by Drummond Matthews of King’s College, correctly interpreted the magnetic stripes on the ocean-floor as marking successive stages in the formation of an ocean basin.

If one ignores those continental pieces that have been affected by orogeny (geological mountain building), these data, together with measurements of the old magnetic fields preserved in continental rocks, enable global reconstructions of the Earth to be made with a high precision back to about 200 million years, and with less much less precision as far back as 600 million years. What the Precambrian Earth was like, i.e. 542-4560 million years, is debatable and the subject of much research.
The results can be visualized by an animation of continental motions to be shown at the end of the talk.