Continental drift
Continental drift is the hypothesis that described the displacement of the continental masses with respect to each other, developed in 1912 by the German Alfred Wegener based on various empirical-rational observations.
Wegener's hypothesis was displaced in the 1960s with the development of plate tectonics, when the movement of the continents could be adequately explained.
History
Forerunners
The Flemish cartographer Abraham Ortelius noted as early as 1596 that the shapes of the continents along the opposite shores of the Atlantic Ocean (particularly Africa and South America) seemed to articulate, and suggested that America would have been "torn" from Europe and Africa (by earthquakes and floods). Francis Bacon in 1620, François Placet in 1658, Theodor Christoph Lilienthal in 1756, Alexander von Humboldt in 1801 and 1845 and Antonio Snider-Pellegrini in 1858 also They made similar comments. In fact, the idea that the Earth would have undergone profound changes of all kinds during its history was widely held until the end of the 19th century. Charles Lyell wrote:
The continents, therefore, although permanent during entire geological periods, change their positions completely in the course of the ages.Principles of Geology (1872)
Mainstream thinking began to change after 1850, under the influence in particular of the American geologist and mineralogist James Dwight Dana, who wrote:
The continents and oceans had their general outline or shape defined in ancient times. This has been shown with respect to North America from the position and distribution of the first beds of the Silurico, those of the Potsdam era.... And this will probably prove the case in Primordial time with the other continents as wellThe continents and oceans had their general outline or form defined in earliest time. This has been proved with respect to North America from the position and distribution of the first beds of the Silurian – those of the Potsdam epoch.... and this will probably prove to the case in Primordial time with the other continents also.Manual of Geology (1863), James D. Dana
In 1889, Alfred Russel Wallace considered the relative displacements of the continents an outdated hypothesis:
Formerly it was a very general belief, even among geologists, that the great characteristics of the earth's surface, not less than the small ones, were subject to continuous mutations, and that during the course of the geologic time known the continents and large oceans had changed place over and over again.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 otherDarwinism: An Exposition of the Theory of Natural Selection (1889), Alfred Russel
The idea that the Americas, Europe, and Asia were once united, however, continued to be advanced by various scholars, including Franklin Coxworthy (between 1848 and 1890), Roberto Mantovani (in 1889 and 1909), William Henry Pickering (in 1907) and Frank Bursley Taylor (in 1908). Eduard Suess also proposed in 1885 and 1893 the past existence of the Gondwana supercontinent and the Tethys Ocean. Some of the arguments that Wegener will later invoke had already been advanced by these predecessors. Montovani, in particular, stressed the similarity of the geological formations of the southern continents, but explained the fracturing of the supercontinent by volcanic activity and the subsequent remoteness of the continents by a supposed thermal expansion of the Earth. Taylor imagined that the continents would have moved by a process of "continental slippage" due to tidal forces during the supposed capture of the Moon during the Cretaceous. Although the mechanism he proposed was unfounded, he was the first to realize that one of the effects of continental shifts was the formation of mountains, and he rightly attributed the formation of the Himalayas to the collision between the Indian subcontinent and Asia (during a In time the drift of the continents will be known as the "Taylor-Wegener hypothesis").
Alfred Wegener's theory
The theory of continental drift was originally proposed in 1912 by the German meteorologist and geophysicist Alfred Wegener (1880-1930), who formulated it based, among other things, on the way in which the shapes of the continents seemed to fit together over time. each side of the Atlantic Ocean, such as Africa and South America, as Benjamin Franklin and others had previously realized. He also took into account the distribution of certain geological formations and the fossil record of the northern continents, which showed that they may have shared flora and fauna in earlier geological times. With these data, Wegener calculated that the set of current continents were united in the remote past of the Earth, forming a supercontinent, called Pangea, which means "all land" in Greek. This approach was initially discarded by most of his colleagues, since his theory lacked a mechanism to explain the drift of the continents. In his original thesis, he proposed that the continents moved on another, denser layer of the Earth, which formed the ocean floor and that it extended below them, in the same way that a carpet moves. However, the enormous frictional force involved led to the rejection of Wegener's explanation and the suspension, as an interesting but unproven hypothesis, of the idea of continental drift. In short, continental drift is the slow and continuous displacement of the continental masses.
The theory today
The theory of continental drift, along with that of the spreading of the ocean floor, were included in the theory of plate tectonics, born in the 1960s from research by Robert Dietz, Bruce C. Heezen, Marie Tharp, Harry Hess, Maurice Ewing, Tuzo Wilson, and others. According to this theory, the phenomenon of displacement has occurred for billions of years thanks to global convection in the mantle (except for the rigid upper part that is part of the lithosphere), on which the lithosphere is permanently reconfigured and displaced..
In this case, it is a consistent explanation, in physical terms, which, although it differs radically about the mechanism of continental displacement, is also a mobilist theory, which allowed us to overcome the old fixist interpretations of orogeny (geosynclinal and contractionism) and of the formation of the continents and oceans. For this reason, Wegener is considered, with all fairness, his precursor and for the same reason both theories are sometimes mistakenly considered one.
Evidence of continental drift
German meteorologist Alfred Wegener assembled convincing evidence in his original thesis that the continents were in continuous motion. The most important were the following.
Geographic evidence
Wegener suspected that the continents might have been joined in times past by observing a strong coincidence between the shape of the continents' coastlines, especially between South America and Africa. If in the past these continents had been united to form only one (Pangea), it is logical that the fragments would fit together. The coincidence is even greater if one takes into account not the current coasts, but the limits of the continental shelves.
Geological evidence
They were based on the discoveries from this certain science. When Wegener assembled all the continents into Pangea, he discovered that there were mountain ranges with the same age and the same kind of rocks on different continents that, according to him, had been united. These accidents continued to an age that could be determined by calculating the age of the orogens.
Paleoclimatic tests
He used certain sedimentary rocks as indicators of the climates in which they originate, drew a map of these ancient climates, and concluded that their distribution would be inexplicable if the continents had remained in their present positions. Due to ancient glaciations, tillites have been found in geologically widely separated areas.
Paleontological evidence
Alfred Wegener also discovered another startling clue. On different continents separated by oceans, he found fossils of the same species, that is, they inhabited both places during the period of their existence. And what's more, among these organisms were some terrestrial ones, such as reptiles or plants, incapable of having crossed oceans, so he deduced that Pangea had existed during the lifespan of these species.