The hypothesis that the relative positions of the continents have changed through geological time (see Figure). Abraham Ortelius noted in AD 1596 the similarity in shape between the eastern coastline of the Americas and the western coastline of Europe and Africa and suggested that the continents had been torn apart by earthquakes and floods. By the end of the nineteenth century, geologists had recognised geological similarities across the oceans and began to construct persuasive arguments that the continents had once been joined. From 1915 to 1929, Alfred Wegener published descriptions of detailed geological and palaeontological similarities across the Atlantic Ocean and argued that all the present-day continents were once assembled in a single supercontinent that he named pangaea (pangea). Wegener’s mechanism for continental drift, however, proved contentious. As there was clear evidence that the Earth responded to vertical forces by flowing vertically, he argued that it could flow horizontally in concert with forces produced by the rotation of the Earth and suggested that as continents drifted apart, new ocean floor was created at the retreating margins. A major debate developed through the 1920s and 1930s as geologists gathered further evidence of continental drift, but physicists were adamant that there was no mechanism for it. Through the 1950s, the study of palaeomagnetism and the construction of apparent polar wander (APW) paths provided further evidence for continental drift, now from geophysics, but still with no indication of a mechanism.
Convincing evidence of a mechanism for continental drift came in the late 1950s and 1960s. In 1960, Hess established that there was abundant volcanism at the mid-ocean ridges (MORs) and proposed a theory of seafloor spreading whereby new sea floor formed at the ridges and spread outwards. Unlike Wegener, Hess proposed that the continents were part of a rigid system that included the ocean floors: sea floor was not only generated at mid-oceanic spreading centres, but descended at oceanic trenches. Geophysicists finally accepted that convection currents in the Earth’s mantle could drive such a system of continental drift. The discovery of symmetrical magnetic anomalies on either side of the mid- ocean ridges led to the acceptance of sea floor spreading and the development of plate tectonics in the mid- 1960s. This maintains that lateral movement of the lithosphere takes place through the formation and destruction of lithosphere-bearing oceanic crust at the boundaries of rigid plates. Since plates include both oceanic crust and continental crust, continental drift is now seen as a necessary consequence of plate tectonics.
An important implication of continental drift is that areas of the Earth’s surface have experienced different climatic and environmental conditions in the geological past, for which evidence is preserved in the geological record. For example, Upper Carboniferous coal-bearing rock sequences in Britain, north-west Europe and northeastern North America imply formation in tropical environments some 300 million years ago. The reconstruction of former continental positions for the past 200 million years can be achieved by removing ocean floor magnetic anomalies younger than the age of the reconstruction. Prior to the formation of Pangaea, palaeogeography is reconstructed using palaeomagnetism and geological evidence.
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Proposal originally based upon similarity of coastline shapes of the circum- Atlantic continents that land masses move independently over the...
Carey S. Warren , Theories of the Earth and Universe: A History of Dogma in the Earth Sciences , Stanford , California : Stanford...
From the birth of geology as an independent science in the late 18th century until early in this century the notion that the continents were...