252 FAMOUS GEOLOGISTS/Wegener Figure Map published in the 1924 book by Koppen and Wegener, Die Klimate der geologischen Vorzeit, showing polar shifts (dashed lines) from the Carboniferous to recent, related to the African table (left, south pole; right, north pole) Bold lines outline the continental blocks; hatched lines represent the Carboniferous (Karbon) period Perm, Permian; Jura, Jurassic; Trias, Triassic; Kreide, Cret aceous; Eozan, Eocene; Miozan, Miocene; Beginn des Quartar, beginning of the Quaternary Die Klimate, he also mentioned convection currents within the Sima; these had been first discussed as a cause of mountain formation by the Vienna geologist Otto Ampferer (1875–1947) in 1906 Wegener also endeavoured to calculate the recent velocity of the relative motion of the continents, though he was well aware that these values must be quite uncertain In his 1912 paper, comparing various longitude determinations for Greenland, he had deduced an increase of the distance to Europe of 11 m year Referring to the lengths of transatlantic cables, he suggested that North America was drifting away from Europe at about m year From Continental Drift to Plate Tectonics The theory of continental drift was long rejected by the majority of geologists Among Wegener’s few followers were the South African Alexander Du Toit (1878–1948), for whom continental drift provided the best explanation of the close similarities between the strata and fossils of Africa and South America, and the Swiss geologist E´ mile Argand (1879–1940), who saw continental collisions as the only means of producing the folded and buckled strata he had observed in the Alps (see Famous Geologists: Du Toit) Nevertheless, Wegener’s explanation of the PermoCarboniferous ice age impressed even his critics Wegener’s reputation as a meteorologist and a polar explorer contributed to keeping his theory alive His work was immediately remembered when, around 1960, surprising data were obtained from the ocean floor: palaeomagnetic patterns alongside the mid-ocean ridges clearly suggested the spreading of the seafloor Within about two decades, Wegener’s principle of horizontal displacements of parts of Earth’s crust became almost universally accepted, although, ironically, the process still lacked a consensus as to its causes, though convection currents in the internal mantle are most commonly advocated It should be noted that Wegener’s original concept differed from modern plate tectonics in essential points, particularly with regard to the Sial and the Sima According to modern theory, the (Sialic) continents not ‘plough’ through the (oceanic) Sima Instead, both continents and ocean floor are regarded as forming solid plates, ‘floating’ on the asthenosphere, which, due to tremendous heat and pressure, behaves like an extremely viscous liquid (as Wegener had thought the Sima did) Therefore, the older term ‘continental drift’, still often used today, is not quite appropriate for the modern concept Notwithstanding these differences, Wegener’s basic ideas remain sound, and the lines of evidence that he used to support his theory are still valid He first envisaged a dynamic Earth, connecting its major features and various geological processes – continental