EAS 1600Introduction to Environmental Sciences____________________________Class 21 - Plate Tectonics: Part 1“From Hypothesis To Theory”____________________________Our discussion of the ocean brings up two Earth System Puzzles:¾based on our understanding of oceanic processes, the ocean’s biota should be running out of nutrients (which should be accumulating at the ocean bottom); and¾the 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”¾Theory and hypothesis are both often used colloquially to mean an untested idea or opinion. ¾According to The American College Dictionary¾Hypothesis: “a proposition (or conjecture) proposed as an explanation for the occurrence of some specified group of phenomena.”¾often serves as the basis of argument or experimentation by which to reach the truth.¾Theory: “a coherent group of general propositions used as principles of explanation for a class of phenomena”¾Law:well-established propositions that are regarded as reporting matters of fact.For example:¾The Gaia Hypothesis¾The kinetic theory of gases; Newton’s theory of gravitation¾The laws of thermodynamicsPlate TectonicsIn the last two lectures we reviewed the basic propertiesof the solid earth and the minerals and rocks that we findon its surface. The rocks hint at the existence of a verydynamic earth. In this lecture we begin our discussion ofplate 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 thatall 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 earthsciences 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 (4thedition)
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