Years before the advent of plate tectonics―the widely accepted theory, developed in the mid-1960â€™s, the holds that the major features of Earth's surface 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 theory that came to be called continental drift, that Earth's continents were mobile. To most geologists today, Wegener's The origin of Continents and Oceans appears an impressive and prescient 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 continental crust; and a causal connection between horizontal displacements and the formation of mountain chains. Yet despite the considerable overlap between Wegenerâ€™s concepts and the later widely embraced plate tectonics theory, and despite the fact that continental drift theory presented a possible solution to the problem of the origin of mountains at a time when existing explanations were seriously in doubt, in its day Wegenerâ€™s theory was rejected by the vast majority of geologists.
Most geologists and many historians today believe that Wegenerâ€™s theory 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 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 explained. The most likely cause for the rejection of continental drift―a cause that has been largely ignored because we consider Wegenerâ€™s theory to have been validated by the theory of plate tectonics―is the nature of the evidence that was put forward to support it. Most of Wegenerâ€™s evidence consisted of homologies' similarities of patterns and forms based on direct observations of rocks in the field, supported by the use of hammers, hand lenses, and field notebooks. In contrast, the data supporting plate tectonics were impressively geophysicalâ€”instrumental determinations of the physical properties of Earth garnered through the use of seismographs, magnetometers, and computers.
Q1:The author cites Hallam on the ice ages primarily in order to
A. provide an example of a geologic phenomenon whose precise causes are not fully understood by geologists today
B. criticize the geological community for an apparent lack of consistency in its responses to new theories
C. offer evidence held to undermine a common view of why Wegener’s theory was not accepted in its day
D. give an example of a modern scientist who believes that Wegener’s theory was rejected because it failed to adequately explain the mechanical basis of continental drift
E. support Gould’s rationale for why Wegener’s theory was rejected by most geologists in the early twentieth century
Q2:The author of the passage refers to the "considerable overlap" between continental drift theory and plate tectonics theory most probably in order to
A. suggest that plate tectonics theory is derived from Wegener’s work
B. introduce a discussion comparing the elements of the two theories
C. examine the question of whether continental drift theory was innovative in its time
D. provide a reason why it might seem surprising that continental drift theory was not more widely embraced by geologists
E. cite an explanation that has been frequently offered for Wegener’s high standing among geologists today
Q3:The author of the passage suggests that the most likely explanation for the geological community’s response to continental drift theory in its day was that the theory
A. was in conflict with certain aspects of plate tectonics theory
B. failed to account for how mountains were formed
C. did not adequately explain how continents moved through the ocean floor
D. was contradicted by the geophysical data of the time
E. was based on a kind of evidence that was considered insufficiently convincing
Q4:It can be inferred from the passage that geologists today would be most likely to agree with which of the following statements about Wegener’s The Origin of Continents and Oceans?
A. It was a worthy scientific effort that was ahead of its time.
B. It was based on evidence that was later disproved.
C. It was directly responsible for the acceptance of the theory of plate tectonics.
D. It has been disproved by continental drift theory.
E. It misrepresented how horizontal displacements cause the formation of mountain chains.