Continental drift and earthquakes
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CONTINENTAL DRIFT AND EARTHQUAKES If you look at a map of the earth, you will notice some things which struck past geologists as peculiar. Have you ever noticed the way South America and Africa seem to fit into each other (if you just move them closer), and the way the Arabian peninsulas seem to fit neatly into the upper right hand corner of Africa? This apparent fit becomes even closer if you include the continental shelf areas of the continents (which are under water and extend outward for a few hundred miles past the present geographical limits of the continents). Could it be that these great land masses were at one time together and have somehow drifted apart? This idea was first presented in 1910 by the German geologist Alfred Wegener. When he presented this theory it was unaccepted, even scoffed at. How could the continents actually move over the surface of the earth? How could they drift apart? At the time Wegener was unable to supply the answer, and for the longest time his theory was not accepted. Not accepted until recent times, until about the 1960's. What caused modern geologists to change their minds and to embrace a theory which they had previously discarded? In the 1960's new evidence came to bear on the problem of continental drift and Wegener's theory. For example, going back to the case of South America and Africa, almost directly halfway between South America and Africa are a series of volcanic islands, which stick up through the waters of the South Atlantic Ocean. Starting with Tristan de Cunha, in the extreme South Atlantic Ocean, and going up to Saint Helena, the Ascension Islands, to the Cape Verde Islands, all the way to Iceland, there seems to be a series of islands connected by more or less a straight line, all of which are volcanic in origin. Geologists were intrigued with the location of these islands being midway between the two great continents which seemingly fit together. Were they related, these islands and the continents of South America? Research in the 1950's indicated that the sea floor along a line connecting these islands was slowly moving apart. It's as if there were a rip at the base of these islands where they meet the ocean floor and the west part of that rip was moving slowly, very slowly to the west, the eastern part moving to the east. This Middle Atlantic Ridge, as it came to be called, seemed to be opening up at about the rate of an inch a year. Furthermore, the ocean seemed to be warmer in the region of the Middle Atlantic Ridge, suggesting that heat from the interior of the earth was coming up through a crack in the ocean floor. Could it be that this was volcanic activity at a very small scale, and that this activity was moving the continents South America and Africa apart? Examination of fossil life in South America and Africa showed that if we went back in time the fossil life seemed more similar, the same animals being found in both places in prehistoric past. Paleontologists also were able to determine that the history of the magnetic orientation of the rocks in South America and Africa seem to match as we went back in time. The evidence mounted up. The continents had been together in the past! Today, the theory of continental drift is fairly well established. The evidence indicates that Wegener was indeed right when he proposed his theory in 1910. Had Wegener had this evidence in 1910, there would have been no question as to the correctness of his thoughts. Geologists now see the entire earth as being made of a series of plates, plates which drift apart from each other, carrying with them, the continents. And if they drift apart, of course they must go into the earth at some other point making a sort of continual circulation of the crust of the earth. It's happening so slowly that we have not, until now, been aware of it. Geologists now conceive of the earth in the past as being a place where the continents were not as wide spread as we now find them. Indeed, the continents seem to be together, in two large groupings. The names of the two land masses are called Godwanaland and Laurasia. Could it be that the earthquake zones of the earth correspond to the regions where the plates are drifting apart and coming together? A map of the earthquake zones of the earth shows that this is indeed exactly the case. In the United States, one of these earthquake zones is in the western part going through California, the so-called Pacific plate, which is moving, piling up forces which are released with a sudden lurch: an earthquake. With the establishment of the theory of continental drift we have once again evidence of the constantly churning interior of the earth, a churning which we can only glimpse by the effect it has on the continents, on the surface. Thus, Wegener's theory, which seemed so laughable when it was first presented now goes a long way to explain and bring together a great deal of isolated data. Directory: asa -> wp-content -> uploads -> 2015 asa -> Asian Pacific Mathematical Olympiad(apmo) asa -> Administrative sciences association of canada associaton des sciences administratives du canada asa -> Cross country asa -> Sport Administration Learnerships asa -> Viljoen third in Lausanne asa -> Nuclear fission 2015 -> The speed of light and reality Download 6.85 Kb. Share with your friends:
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