Discuss the degree to which the theory of plate tectonics is supported by seismic and volcanic activity

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Discuss the degree to which the theory of plate tectonics is supported by seismic and volcanic activity.

The theory of plate tectonics suggests that the earth’s lithosphere is split into plates (as shown in map 1). At their boundaries the plates submerge, diverge and slide past one another, this movement is caused by convection currents in the asthenosphere. The idea that the plates are moving is not new, as early as 1620 the English philosopher Francis Bacon was aware that the continents seemed to fit together. In 1912 Wegener suggested that the continents were once joined as the super continent Pangaea (as seen in image 4) and that they had drifted apart, he gathered a large amount of evidence to support this theory. Continents appear to fit together, more significantly so if continental shelves are taken to be the true edges of the land mass. There is a vast array of geological evidence that includes similar glacial deposits being found in Antarctica, S. America and India. Antarctica, Svalbard, N. America and the UK all contain coal deposits of a similar age that were formed in tropical conditions, they are no longer in tropical climate zones. Biological evidence is also available, Marsupials are only found in Australia because the predator that wiped them out elsewhere had not migrated there before it drifted away from the main super continent.

Despite this evidence, his theory was initially rejected due to lack of explanation for how continents could move over the earth. However in 1948 a survey of the ocean floor found a ridge running north to south beneath the Atlantic Ocean. During the 1950’s magnetic surveys of the ocean floor showed regular patterns of palaeomagnetic striping about the ridges. When lava erupts, iron rich minerals within it are aligned with the earth’s magnetic field, this is fixed as the lava cools and they record the earth’s polarity at the time they cool. The earth’s polarity reverses approximately every 400,000 years and bands of polarity are mirrored either side of the mid-ocean ridge suggesting new rocks are added equally either side. This suggests that the sea floor is spreading, and logically, as the earth’s size is not increasing, some crust must be being destroyed. This can be taken to explain how the continents drifted.

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The shift and contact of the rigid plates that make up the earth, causes earthquakes, volcanic activity, the presence of mountains and other geographical occurrences. It can therefore be understood that seismic and volcanic activity will occur at plate margins. This essay will evaluate the extent to which this is true, and thus how far the theory of plate tectonics is supported by such phenomena.

Volcanoes are openings in the earth’s crust through which lava, ash and gases erupt. Lava is taken as proof of the magma that comprises the mantle beneath the earth’s crust.  The majority ...

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This is an excellent answer for an A level student. The author has a sound understanding of the topic, and has an awareness of what the question requires. Use of technical terms is generally very good, and relevant examples are well-explained. In a few places a little more explanation would improve the answer. Overall worth *****