Continental drift is the hypothesis that the Earth's continents have moved over geologic time relative to each other, thus appearing to have "drifted" across the ocean bed. The concept was independently and more fully developed by Alfred Wegener in , but his hypothesis was rejected by many for lack of any motive mechanism. Arthur Holmes later proposed mantle convection for that mechanism. The idea of continental drift has since been subsumed by the theory of plate tectonics , which explains that the continents move by riding on plates of the Earth's lithosphere.
Abraham Ortelius Ortelius ,  Theodor Christoph Lilienthal ,  Alexander von Humboldt and ,  Antonio Snider-Pellegrini Snider-Pellegrini , and others had noted earlier that the shapes of continents on opposite sides of the Atlantic Ocean most notably, Africa and South America seem to fit together. Kious described Ortelius' thoughts in this way: . Abraham Ortelius in his work Thesaurus Geographicus In , Alfred Russel Wallace remarked, "It was formerly a very general belief, even amongst geologists, that the great features of the earth's surface, no less than the smaller ones, were subject to continual mutations, and that during the course of known geological time the continents and great oceans had, again and again, changed places with each other.
In his Manual of Geology , Dana wrote, "The continents and oceans had their general outline or form defined in earliest time.
This has been proved with regard to North America from the position and distribution of the first beds of the Lower Silurian , — those of the Potsdam epoch. The facts indicate that the continent of North America had its surface near tide-level, part above and part below it p. And, if the outlines of the continents were marked out, it follows that the outlines of the oceans were no less so". This appeared to be confirmed by the exploration of the deep sea beds conducted by the Challenger expedition , —, which showed that contrary to expectation, land debris brought down by rivers to the ocean is deposited comparatively close to the shore on what is now known as the continental shelf.
This suggested that the oceans were a permanent feature of the Earth's surface, and did not change places [ clarification needed ] with the continents. Apart from the earlier speculations mentioned in the previous section, the idea that the American continents had once formed a single landmass together with Europe and Asia before assuming their present shapes and positions was postulated by several scientists before Alfred Wegener 's paper. For example: the similarity of southern continent geological formations had led Roberto Mantovani to conjecture in and that all the continents had once been joined into a supercontinent ; Wegener noted the similarity of Mantovani's and his own maps of the former positions of the southern continents.
In Mantovani's conjecture, this continent broke due to volcanic activity caused by thermal expansion , and the new continents drifted away from each other because of further expansion of the rip-zones, where the oceans now lie. This led Mantovani to propose an Expanding Earth theory which has since been shown to be incorrect. Continental drift without expansion was proposed by Frank Bursley Taylor ,  who suggested in published in that the continents were moved into their present positions by a process of "continental creep".
Although his proposed mechanism was wrong, he was the first to realize the insight that one of the effects of continental motion would be the formation of mountains, and attributed the formation of the Himalayas to the collision between the Indian subcontinent with Asia. In the midth century, the theory of continental drift was referred to as the "Taylor-Wegener hypothesis",    although this terminology eventually fell out of common use.
Wegener was the first to use the phrase "continental drift" ,   in German "die Verschiebung der Kontinente" — translated into English in and formally publish the hypothesis that the continents had somehow "drifted" apart.
Although he presented much evidence for continental drift, he was unable to provide a convincing explanation for the physical processes which might have caused this drift. His suggestion that the continents had been pulled apart by the centrifugal pseudoforce Polflucht of the Earth's rotation or by a small component of astronomical precession was rejected, as calculations showed that the force was not sufficient.
The theory of continental drift was not accepted for many years. One problem was that a plausible driving force was missing. Other geologists also believed that the evidence that Wegener had provided was not sufficient. It is now accepted that the plates carrying the continents do move across the Earth's surface, although not as fast as Wegener believed; ironically one of the chief outstanding questions is the one Wegener failed to resolve: what is the nature of the forces propelling the plates?
The British geologist Arthur Holmes championed the theory of continental drift at a time when it was deeply unfashionable. He proposed in that the Earth's mantle contained convection cells which dissipated heat produced by radioactive decay and moved the crust at the surface.
Geological maps of the time showed huge land bridges spanning the Atlantic and Indian oceans to account for the similarities of fauna and flora and the divisions of the Asian continent in the Permian period but failing to account for glaciation in India, Australia and South Africa. Geophysicist Jack Oliver is credited with providing seismologic evidence supporting plate tectonics which encompassed and superseded continental drift with the article "Seismology and the New Global Tectonics", published in , using data collected from seismologic stations, including those he set up in the South Pacific.
It is now known that there are two kinds of crust: continental crust and oceanic crust. Continental crust is inherently lighter and its composition is different from oceanic crust, but both kinds reside above a much deeper " plastic " mantle. Oceanic crust is created at spreading centers , and this, along with subduction , drives the system of plates in a chaotic manner, resulting in continuous orogeny and areas of isostatic imbalance. The theory of plate tectonics explains all this, including the movement of the continents, better than Wegener's theory.
Hans Stille and Leopold Kober opposed the idea of continental drift and worked on a "fixist"  geosyncline model with Earth contraction playing a key role in the formation of orogens. Bernauer correctly equated Reykjanes in south-west Iceland with the Mid-Atlantic Ridge , arguing with this that the floor of the Atlantic Ocean was undergoing extension just like Reykjanes. David Attenborough , who attended university in the second half of the s, recounted an incident illustrating its lack of acceptance then: "I once asked one of my lecturers why he was not talking to us about continental drift and I was told, sneeringly, that if I could prove there was a force that could move continents, then he might think about it.
The idea was moonshine, I was informed. As late as — just five years before Carey  introduced the theory of plate tectonics — the theory of continental drift was rejected by the physicist Scheidegger on the following grounds. From the s to the late s, works by Vening-Meinesz , Holmes, Umbgrove , and numerous others outlined concepts that were close or nearly identical to modern plate tectonics theory. In particular, the English geologist Arthur Holmes proposed in that plate junctions might lie beneath the sea , and in that convection currents within the mantle might be the driving force.
However, scientific communication in the '30 and '40s was inhibited by the war , and the theory still required work to avoid foundering on the orogeny and isostasy objections. Worse, the most viable forms of the theory predicted the existence of convection cell boundaries reaching deep into the earth that had yet to be observed. In , a team of scientists led by Maurice Ewing confirmed the existence of a rise in the central Atlantic Ocean, and found that the floor of the seabed beneath the sediments was chemically and physically different from continental crust.
An important conclusion was that along this system, new ocean floor was being created, which led to the concept of the " Great Global Rift ". Meanwhile, scientists began recognizing odd magnetic variations across the ocean floor using devices developed during World War II to detect submarines. In a series of papers in —, Heezen, Dietz, Hess, Mason, Vine, Matthews, and Morley collectively realized that the magnetization of the ocean floor formed extensive, zebra-like patterns: one stripe would exhibit normal polarity and the adjoining stripes reversed polarity.
New magma from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. The new crust is magnetized by the earth's magnetic field, which undergoes occasional reversals. Formation of new crust then displaces the magnetized crust apart, akin to a conveyor belt — hence the name. Without workable alternatives to explain the stripes, geophysicists were forced to conclude that Holmes had been right: ocean rifts were sites of perpetual orogeny at the boundaries of convection cells.
In addition, Marie Tharp , in collaboration with Bruce Heezen , who initially ridiculed Tharp's observations that her maps confirmed continental drift theory, provided essential corroboration, using her skills in cartography and seismographic data, to confirm the theory. Evidence for the movement of continents on tectonic plates is now extensive. Similar plant and animal fossils are found around the shores of different continents, suggesting that they were once joined.
The fossils of Mesosaurus , a freshwater reptile rather like a small crocodile, found both in Brazil and South Africa , are one example; another is the discovery of fossils of the land reptile Lystrosaurus in rocks of the same age at locations in Africa , India , and Antarctica.
The complementary arrangement of the facing sides of South America and Africa is obvious but a temporary coincidence. In millions of years, slab pull , ridge-push , and other forces of tectonophysics will further separate and rotate those two continents. It was that temporary feature that inspired Wegener to study what he defined as continental drift although he did not live to see his hypothesis generally accepted. The widespread distribution of Permo-Carboniferous glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift.
The continuity of glaciers, inferred from oriented glacial striations and deposits called tillites , suggested the existence of the supercontinent of Gondwana , which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, based on continents' current positions and orientations, and supported the idea that the southern continents had previously been in dramatically different locations that were contiguous with one another.
From Wikipedia, the free encyclopedia. The movement of the Earth's continents relative to each other. This article is about the development of the continental drift hypothesis before For the contemporary theory, see plate tectonics. For the Russell Banks novel, see Continental Drift novel. Further information: Timeline of the development of tectonophysics before See also: Early modern Netherlandish cartography and geography. Main article: Plate tectonics. Archived from the original on 27 July Retrieved 29 January University of Frankfurt.
Retrieved 6 December Freytag, , page From p. From page "This ocean we designate by the name "Tethys", after the sister and consort of Oceanus. The latest successor of the Tethyan Sea is the present Mediterranean.
Columbia University Press. Archived from the original on 3 June Retrieved 20 October Archived from the original on 11 April Retrieved 23 August Wegener's inability to provide an adequate explanation of the forces responsible for continental drift and the prevailing belief that the earth was solid and immovable resulted in the scientific dismissal of his theories.
Transactions of the Geological Society of Glasgow. Archived PDF from the original on 9 October Retrieved 15 January Principles of Physical Geology 1st ed. The New York Times. Archived from the original on 26 May Retrieved 6 June Journal of Geophysical Research. Bibcode : JGR The Observer. Archived from the original on 31 October Retrieved 29 October Carey, S. Hobart: Univ.