Scientists formerly believed that the rocky planetsEarth, Mercury, Ve

Question

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. Tat 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 thereafer. 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 planetesi mals became larger, their numbers decreased. Consequently, the number of collisions between planetesimals decreased.     1  
 For the following question, consider each of the choices separately and select all that apply.

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

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.

2 
 2. Which of the following best describes the “observation” ( highlighted ) 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.

Sajjad1994 · Answer

Passage Summary

The passage describes two theories of planetary formation in the solar system: the rapid collapse theory and the accretion theory. Te passage mentions that the former theory was dominant before the 1960s and discusses how data obtained in the 1960s reignited scientifc interest in the latter theory.

Sajjad1994 · Answer

OE

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

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.

Answer: A

Sajjad1994 · Answer

OE

2. Which of the following best describes the “observation” (     highlighted     ) referred to in the passage?

The  “observation”  mentioned in the passage is the fnding 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 thereafer.”  The answer choice that is closest in meaning to this description is  Choice D.

Answer: D

Scientists formerly believed that the rocky planetsEarth, Mercury, Ve

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