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# OG_VPR # 24/25 Scientists formerly believed that the rocky p

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OG_VPR # 24/25 Scientists formerly believed that the rocky p [#permalink]  12 Oct 2016, 13:19
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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.
For the following question, consider each of the choices separately and select all that apply.

The passage provides evidence that Schmidt would be likely to disagree with the theory presented in the first sentence over

• the length of time it took for the rocky planets to form.
• the most likely causes of the Moon’s impact craters.
• the importance of cosmic dust as a seminal material in planetary formation.

[Reveal] Spoiler: OA
A

Which of the following best describes the “observation” (line 6) referred to in the passage?

A) The rocky planets were created by the rapid gravitational collapse of a dust cloud.
B) Certain features on the Moon’s surface are impact craters caused by collisions with objects such as planetesimals.
C) The rocky planets were formed by a slow accretion of cosmic dust into increasingly larger bodies.
D) The number of objects colliding with the Moon appears to have been high for a while and then rapidly diminished.
E) There are far fewer planetesimals in existence today than there were about 4.5 billion years ago.

[Reveal] Spoiler: OA
D

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Question: 24-25
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Re: OG_VPR # 24/25 Scientists formerly believed that the rocky p [#permalink]  12 Oct 2016, 13:21
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Explanation

24) 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.

25) The “observation” mentioned in the passage is the finding that Moon’s 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.” The answer choice that is closest in meaning to this description is Choice D.
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Re: OG_VPR # 24/25 Scientists formerly believed that the rocky p   [#permalink] 12 Oct 2016, 13:21
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