Wegener was right about Pangaea but wrong about what split it
Alfred Wegener argued in 1912 that all the continents had once been a single landmass. He was correct, yet the idea stalled for decades because his explanation, that Earth's spin flung the continents apart, was physically impossible. Only mantle convection and postwar maps of the seafloor turned his supercontinent, Pangaea, into textbook science.
Pangaea assembled from Gondwana, Euramerica and Siberia around 335 million years ago, during the Carboniferous, and started splitting up some 175 million years ago, as the Jurassic opened. It was shaped like a C, stretching from pole to pole, and was surrounded by the superocean Panthalassa and the Tethys seas. Its name joins Greek words for 'all' and 'Earth'. Wegener used it just once, in the 1920 edition of his book, and it entered English literature in 1926, notably at a petroleum geologists' symposium.
The earliest hint was simply the shape of the Atlantic coasts. Abraham Ortelius may have suggested in 1596 that the continents had once been joined, and careful reconstructions later showed that the mismatch between the Americas and Europe and Africa, measured at the 500-fathom depth contour, is under 130 kilometres, too close for chance. The Appalachians line up with the Caledonides of Scandinavia as parts of one former range, and glacial till of identical age appears on continents now far apart.
Fossils sealed the case. Remains of the reptile-like Lystrosaurus turn up in South Africa, India and Antarctica, and the freshwater reptile Mesosaurus is known only from pockets of coastal Brazil and West Africa, an ocean apart. Magnetic minerals in rocks record the latitude where they formed, so once the wandering of the magnetic pole is subtracted, the drift of the continents themselves can be reconstructed.
Pangaea was probably not the first. Supercontinents seem to form and break up in cycles. An earlier one, Columbia or Nuna, may have assembled 2.0 to 1.8 billion years ago; Rodinia existed from about 1.3 billion to 750 million years ago. Reconstructions of these older giants remain partly speculative, which is why Pangaea, the most recent, is by far the best understood.
Source: Pangaea
