Reflects so that little of the polar ice melts during

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reflects so that little of the polar ice melts during the summer; if it did Answer: ------------------------------------------------------------------------------------------------------------ Q24 to Q27: Years before the advent of plate tectonics―the widely accepted theory, developed in the mid-1960’s, the holds Line that the major features of Earth’s surface (5) are created by the horizontal motions of Earth’s outer shell, or lithosphere― a similar theory was rejected by the geological community. In 1912, Alfred Wegener proposed, in a widely debated (10) theory that came to be called continental drift, that Earth’s continents were mobile. 12
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To most geologists today, Wegener’s The origin of Continents and Oceans appears an impressive and prescient (15) document, containing several of the essential presumptions underlying plate tectonics theory: the horizontal mobility of pieces of Earth’s crust; the essential difference between oceanic and conti- (20) nental crust; and a causal connection between horizontal displacements and the formation of mountain chains. Yet despite the considerable overlap between Wegener’s concepts and the (25) later widely embraced plate tectonics theory, and despite the fact that conti- nental drift theory presented a possible solution to the problem of the origin of mountains at a time when existing expla- (30) nations were seriously in doubt, in its day Wegener’s theory was rejected by the vast majority of geologists. Most geologists and many historians today believe that Wegener’s theory (35) was rejected because of its lack of an adequate mechanical basis. Stephen Jay Gould, for example, argues that continental drift theory was rejected because it did not explain how continents (40) could move through an apparently solid oceanic floor. However, as Anthony Hallam has pointed out, many scientific phenomena, such as the ice ages, have been accepted before they could be fully (45) explained. The most likely cause for the rejection of continental drift―a cause that has been largely ignored because we consider Wegener’s theory to have been validated by the theory of plate (50) tectonics―is the nature of the evidence that was put forward to support it. Most of Wegener’s evidence consisted of homologies—similarities of patterns and forms based on direct observations of (55) rocks in the field, supported by the use of hammers, hand lenses, and field note- books. In contrast, the data supporting 13
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plate tectonics were impressively geophysical—instrumental determinations (60) of the physical properties of Earth gar- nered through the use of seismographs, magnetometers, and computers. --------------------------------------------------------------------------------
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