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Lecture19_TectonicsI - EAS 1600 Introduction to...

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EAS 1600 Introduction to Environmental Sciences ____________________________ Class 21 - Plate Tectonics: Part 1 “From Hypothesis To Theory” ____________________________ Our discussion of the ocean brings up two Earth System Puzzles: ¾ based on our understanding of oceanic processes, the ocean’s biota should be running out of nutrients (which should be accumulating at the ocean bottom); and ¾ the ocean should have filled in with material from the eroding continents a long time ago. This leads to consider the ‘solid’ earth “From Hypothesis To Theory To Law” ¾ Theory and hypothesis are both often used colloquially to mean an untested idea or opinion. ¾ According to The American College Dictionary ¾ Hypothesis : “a proposition (or conjecture) proposed as an explanation for the occurrence of some specified group of phenomena.” ¾ often serves as the basis of argument or experimentation by which to reach the truth. ¾ Theory : “a coherent group of general propositions used as principles of explanation for a class of phenomena” ¾ Law: well-established propositions that are regarded as reporting matters of fact. For example: ¾ The Gaia Hypothesis ¾ The kinetic theory of gases; Newton’s theory of gravitation ¾ The laws of thermodynamics Plate Tectonics In the last two lectures we reviewed the basic properties of the solid earth and the minerals and rocks that we find on its surface. The rocks hint at the existence of a very dynamic earth. In this lecture we begin our discussion of plate tectonics – a unified theory of the solid earth that explains many of the puzzles that we identified in previous lectures. We start our discussion with the life of Alfred Wegener ... "Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence. . . It is only by combing the information furnished by all the earth sciences that we can hope to determine ’truth’ here, that is to say, to find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw." Alfred Wegener. The Origins of Continents and Oceans (4 th edition)
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