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  3. Scientists formerly believed that the rocky planets—Earth, Mercury, Venus, and M

Scientists formerly believed that the rocky planets—Earth, Mercury, Venus, and M

游客2025-02-21  12
问题 Scientists formerly believed that the rocky planets—Earth, Mercury, Venus, and Mars—were created by the rapid gravitational collapse of a dust cloud, a deflation giving rise to a dense orb. That view was challenged in the 1960s, when studies of Moon craters revealed that these craters were caused by the impact of objects that were in great abundance about 4.5 billion years ago but whose number appeared to have quickly decreased shortly thereafter. This observation rejuvenated Otto Schmidt’s 1944 theory of accretion. According to this theory, cosmic dust gradually lumped into ever-larger conglomerates: particulates, gravel, small and then larger balls, planetesimals(tiny planets), and, ultimately, planets. As the planetesimals became larger, their numbers decreased. Consequently, the number of collisions between planetesimals decreased. [br] The passage provides evidence that Schmidt would be likely to DISAGREE with the theory presented in the first sentence over
选项 A、the length of time it took for the rocky planets to form
B、the most likely causes of the Moon’s impact craters
C、the importance of cosmic dust as a seminal material in planetary formation
答案 A
解析 Choice A is correct. The question asks what Schmidt would disagree with in the rapid-collapse theory.
Choice A is correct: According to Schmidt’s own theory, "cosmic dust gradually lumped into ever-larger conglomerates"; this means that planetary formation was a prolonged process, while in the rapid-collapse theory, it happened quickly.
Choice B is incorrect: Both theories agree that Moon craters were caused by the impact of cosmic bodies that crashed into the Moon’s surface.
Choice C is incorrect: Both theories agree that cosmic dust was the material from which the planets ultimately formed.
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