History Theory
The basis of theoretical geology beginning of XX century was the contraction hypothesis. The Earth cools like a baked apple, and her wrinkles appear in the form of mountain ranges. Developed these ideas geosyncline theory founded on the basis of study of folded structures. This theory was formulated by James Dana, who added to the contraction hypothesis principle of isostasy. According to this concept of the Earth consists of granites (continents) and basalts (oceans). When you compress the Earth's oceans, the depressions occur tangential force that presses on the continents. Last surging into mountains, and then destroyed. The material, which is obtained as a result of the destruction is delayed in the depressions.
Against this scheme was made by German scientist Alfred Wegener, a meteorologist. January 6, 1912 he addressed a gathering of the German Geological Society reported on the drift of continents. The starting point for the creation of the theory was a coincidence outlines the west coast of Africa and eastern South America. If the continents move, they coincide, as if formed by splitting one pramaterika.
Wegener was not satisfied with the coincidence in shape of the coast (which has repeatedly been noticed before), and an intensive search for evidence of the theory. To do this, he studied geology coasts of both continents, and found many similar geological complexes, which coincided with the combination, as well as the coastline. Another direction of the proof of the theory have paleoclimatic reconstruction, palaeontological and biogeographical arguments. Many animals and plants have limited ranges, on both sides of the Atlantic Ocean. They are very similar, but are separated by many kilometers of water space, and it is difficult to assume that they have crossed the ocean.
In addition, Wegener began to look for geophysical and geodetic evidence. However, while the level of science was clearly not sufficient to fix the modern movement of continents. In 1930 Wegener died during an expedition in Greenland, but before his death knew that the scientific community has not accepted his theory.
The original theory of continental drift was accepted by the scientific community favorably, but in 1922 she has been strongly criticized by several well-known experts. The main argument against the theory became a matter of force that moves the plate. Wegener suggested that continents move on basalts of the ocean floor, but this required a tremendous effort, and the source of this force one to call but could not. As a source of plate motion proposing the Coriolis force, tidal phenomena, and some others, but simple calculation shows that all of them are absolutely inadequate for moving large continental blocks.
Critics of the theory of Wegener placed at the heart of the issue of force, moving the continents, and ignored the whole set of facts, clearly confirm the theory. In fact, they found only one issue on which the new concept was powerless, and without constructive criticism rejected key evidence. After the death of Alfred Wegener's theory of continental drift was rejected, receiving marginal status of science, and the vast majority of studies continued to be held in the framework of the geosyncline. True, she had to seek an explanation of the history of the resettlement of animals on the continents. To do so, were invented by land bridges connecting the continents, but foundered in the deep. This was yet another birth legend of Atlantis. It is worth noting that some scientists do not accept the verdict of the world's authority and continued to search for evidence of movement of the continents. So du Toit (Alexander du Toit) explained the formation of the Himalayan mountains of India and the clash of the Eurasian plate.
Sluggish fight fiksistov as supporters called the lack of significant horizontal displacements, and mobilists who claimed that the continents still moving, with reinvigorated in 1960 when as a result of studying the ocean floor were found the keys to understanding the "machine" called Earth.
By the beginning of 1960 was composed of relief map of the world ocean, which showed that in the center of the oceans are the mid-ocean ridges that rise on 1,5-2 km above the abyssal plains, covered with sediment. These data allowed R. Ditsu and Harry Hessa in 1962-1963 hypothesize spreading. According to this hypothesis, in the mantle convection occurs at a rate of about 1 cm / year. Ascending branch of the convection cells endure a mid-ocean ridges mantle material, which updates the ocean floor in the axial part of the ridge every 300-400 years. Continents do not float on the ocean crust, mantle and move on, being passively "soldered" to the lithospheric plates. Under the concept of spreading, ocean basins structure inconstant and unstable, as the continents - stable.
In 1963, spreading hypothesis receives strong support in connection with the opening of the strip of magnetic anomalies of the ocean bottom. They were interpreted as recording reversals of the geomagnetic field, recorded in the magnetization of ocean floor basalts. After that plate tectonics began a triumphant march in geosciences. More and more scientists to understand that, than spend time on defense concept fiksizma better look at the planet in terms of new theory and, finally, begin to give the real explanation of complex Earth processes.
Now plate tectonics confirmed by direct measurements of the velocity of plates using interferometry of radiation from distant quasars, and measurements using satellite navigation systems, GPS. The results of long-term studies have confirmed the basic tenets of the theory of plate tectonics.