Like Charles Darwin, Alfred Wegener revolutionized an entire science. Unlike Darwin’s ideas, which still stir up much controversy, Wegener’s theory of drifting continents is accepted almost without question, but it did not succeed without a struggle.
In 1912 Wegener suggested that Africa and South America are estranged pieces of a single, ancient supercontinent, Pangaea, that had drifted apart, leaving the Atlantic Ocean between them. However, even Wegener believed that geological wear and tear over the ages would have damaged the fine detail of ancient coastlines, destroying the best evidence for drift. He never tested the fit between African and South American coastlines with any exactitude, and for a time his ideas were virtually ignored. In 1924 Harold Jeffreys, who would become one of the strongest critics of the theory, dismissed it in his landmark book The Earth. Apparently after casually observing the shorelines on a globe, Jeffreys concluded that the fit between Africa and South America was very poor.
Disturbed by Jeffreys’obviously perfunctory observation, S. W. Carey used careful techniques of geometric proportion to correct, better than most maps do, for the fact that the continents’ margins lie on a sphere rather than on a flat surface. He found a remarkably close fit. At about the same time, Keith Runcorn found other evidence for drift. When volcanic lava cools and hardens into basalt, it is magnetized by the earth’s own magnetic field. The rock’s poles become aligned with the earth’s magnetic poles. Though the Planet’s poles have wandered over the past few hundred million years, the magnetic field of each basalt garment is still aligned the way the earth’s poles were at the rime the rock was formed. Although one would expect that the magnetic fields of rocks of the same age from any continent would all be aligned the same way the earth’s magnetic field was aligned at that time, the magnetic fields of basalts in North America are now aligned quite differently from rocks formed in the same epoch in Europe. Thus, the rocks provided clear evidence that the continents had drifted with respect to each other. True to form, Jeffreys brusquely rejected Runcorn’s studies. His casual disdain for such observational data led some field geologists to suggest that his classic should be retitled An Earth.
In 1966 compelling proof that the seafloor spreads from the midocean ridges confirmed the hypothesis that molten rock wells up at these ridges from deep within the earth and repaves the seafloor as giant crustal plates move apart. Thus, seafloor spreading not only explained the long-standing puzzle of why the ocean basins are so much younger than the continents, but also provided evidence that the plates, and so the continents on them, move. Overnight, plate tectonic theory, with continental drift, became the consensus view.
1) Which of the following best expresses the main idea of the passage?(A) Confirmation of Wegener’s theory of continental drift came from unexpected sources.
(B) Critics of Wegener’s theory of continental drift provided information that contributed to its final acceptance
(C) The history of the theory of continental drift is similar in a number of ways to the history of Darwin’s most important theory.
(D) Though Wegener’s theory of continental drift is now generally accepted, Wegener himself was unable to provide any evidence of its accuracy.
(E) Though Wegener’s theory of continental drift had significant implications, many years and much effort were required to win its acceptance.
2. Jeffreys’ approach to Wegener’s theory is most like the approach of which one of the following?(A) a botanist who concludes that two species are unrelated based on superficial examination of their appearance
(B) a driver who attempts to find a street in an unfamiliar city without a map
(C) a zoologist who studies animal behavior rather than anatomy
(D) a politician who bases the decision to run for office on the findings of a public opinion poll
(E) a psychiatrist who bases treatment decisions on patients’ past histories
3. According to the passage, evidence of seafloor spreading helped to explain which one of the following?(A) the reason for the existence of the giant crustal plates on which the continents are found
(B) the reason basalts retain their magnetic field alignments
(C) the reason the earth’s poles have wandered
(D) the composition of the giant crustal plates on which the continents are found
(E) the disparity between the age of the continents and that of the ocean basins
4. Which one of the following phrases, as used in context, most clearly reveals the author’s opinion about Jeffreys?(A) “virtually ignored”
(B) “very poor”
(C) “obviously perfunctory”
(D) “careful techniques”
(E) “consensus view”
5. The author’s mention of the fact that some field geologists suggested calling Jeffreys’ work An Earth serves to(A) contrast two of Jeffreys’ ideas
(B) justify criticisms of Jeffreys’ work
(C) emphasize an opinion of Jeffreys’ work
(D) explain the reasons for Jeffreys’ conflict with Wegener
(E) support an assertion about Jeffreys’ crticis
6. It can be inferred that Carey believed Jeffreys’ 1924 appraisal to be(A) authoritative and supported by indirect evidence
(B) obvious but in need of interpretation
(C) accurate but in need of validation
(D) unquestionably based on insufficient research
(E) so deficient as to be unworthy of investigation
7. The information in the passage suggests that which one of the following findings would most clearly undermine evidence for the theory of continental drift?(A) It is discovered that the ocean basins are actually older than the continents
(B) New techniques of geometric projection are discovered that make much more accurate mapping possible
(C) It is determined that the magnetic fields of some basalts magnetized in Europe and North America during the twentieth century have the same magnetic field alignment
(D) It is found that the magnetic fields of some contemporaneous basalts in Africa and South America have different magnetic fields
(E) It is determined that Jeffreys had performed careful observational studies of geological phenomena