The development of the theory of plate tectonics
The development of the theory of plate tectonics from Continental Drift to the present The theory of continental drift first came to be in 191 5 when Alfred Wagoner first proposed his belief that 300 billion years ago there was one single superscription, Pangaea. At the time, most did not believe it was true as he had no proof or idea of how the masses of land would move. However, new evidence was put forward over time that fit with Westerner's beliefs. The first key piece of evidence is the shape of each continent.
On a map of the earth, it is clear that, if moved together, the intents would fit together very well due to the similarities of coastlines such as those of east South America and West Africa; with the best fit being runarounds meters below sea level. Although they do not fit together perfectly, any irregularities can be explained. Gaps form due to the erosion of coastlines by the sea by abrasion and hydraulic action and areas where land overlaps are due either to volcanic activity creating new land when eruptions occur or changes in sea or land levels since the continents were separated.
In addition, there is also the idea of a geological fit. South America and West Africa, when mapped, showed that many rock outcrops, some over 2000 million years old, continued across the two continents, implying that that both were once in the same place. This could also explain how parts of England can house coal or sandstone despite being in the wrong climate. Furthermore, there are many examples of fossils found on separate continents and nowhere else. This suggests that they were once Joined as it would be almost impossible for an animal to swim thousands of miles in order to breed as this contradicts the theory of evolution.
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Fragments of old fold mountain belts, aged between 400-450 million years old, are found on widely spread continents in the present. For example, pieces of the Caledonia fold mountain belt can be found in many different areas including Scotland, Canada and Scandinavia. This idea can be confirmed when these countries are mapped as one single mass as the mountain belt is shown to be continuous when resembled. Glacial deposits also provide evidence of continental drift. Deposits formed during the late Carboniferous glaciations are found in Antarctica, Africa and South America.
If the continents hadn't moved then the ice sheet would have had to extend from the South Pole to the equator whereas, if reassembled near the South Pole, the size becomes much more reasonable. Likewise, striations on bedrock show the directions of glacial movement and suggest that it flowed from a single point. A more recent development also supported Westerner's theory. In the sass's the mid- Atlantic ridge was discovered by Harry Hess after he used sonar to map the ocean floor. He found that across the Atlantic, the ocean became shallower in the middle ND deeper near the continental margins.
This intern led to the idea of sea floor spreading, giving the theory an idea of how the continents moved something that Wagoner could not do when he first developed this idea. Further evidence of this was Tuna Day two clients name Drummond Matthews Ana Frederick Vine. Lightener, they looked at the magnetism of magma as, when cooled, the iron in the rock aligns to that of the magnetic field of the earth at the time. When measuring, they found that some of the basalt showed a normal magnetic field but others showed a reversed field.
They mapped the rocks, which showed that either side of the mid- ocean ridges the pattern was symmetrical. Furthermore, when the samples were dated it was discovered that rocks of the same time period had the same magnetic field. This created the idea of paleontologist where, over time, the magnetic field of the earth flips due to its flowing core. This new idea added to the theory of continental drift as the dated samples of basalt indicated that as you moved further away from the mid-ocean ridges, the rocks are older showing that the rock created at the centre of the ridge must be pushed aside.
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