Crack down GRE Reading Comprehension
Each passage in this section is followed by several questions. After reading the passage, choose the best answer to each question based on the content of the passage. Answer all questions following the passage on the basis of what is stated or implied on the passage.
RC: I submit that impact of solid bodies is the most fundamental of all interstellar processes that have taken place on the terrestrial planets: without impact, Earth, Mars, Venus, and Mercury would not exist.
Simply put, the collision of smaller objects is the process by which the terrestrial planets were born. On the surface, that the geological record of the earliest history of impacts on the terrestrial planets has been lost, is troubling. As the process is self-erasing, to a certain extent, the earliest record would have been lost even if processes of melting and internal evolution of the planets had not occurred. But much of the record of the last stages of accretion of the planets is preserved, especially on the moon, Mercury, and Mars. In fact, the last stage of accretion is still going on, albeit at a very slow rate.
This is fortunate, because we can study many aspects of the processes of planetary birth by investigation of the nature of small bodies that still exist, the dynamics of their orbital evolution, and the effects that they produce when they ultimately collide with a planet. If impact and accretion were not still occurring, it would be hard to come to grips with a number of difficult problems of planetary origin and early evolution.
It can be most reasonably inferred that which of the following accounts for the lack of a geological record concerning the history of impacts on the planets?
(A) the violence of the initial impact
(B) an outcome that is not self-erasing
(C) a process of change in planets themselves
(D) the absence of proof relating to a hypothetical collision
(E) the ongoing process of accretion
Explanation: The passage mentions that "the geological record…has been lost." In the following sentence, it mentions that "melting and internal evolution" can erase the early geological history of a planet. Therefore, we can infer that a process within the planet themselves can erase the geological record.
(A) is incorrect because nowhere does it mention the violence of any initial impact.
(B) is the opposite of what we are looking for. The processes that do not leave any record of the geological history are self-erasing.
(D) is incorrect since the passage does not talk about this hypothetical collision.
While accretion is still occurring, it does not account for why there is no geological record of the history of planet. Thus (E) is wrong
The author suggests that at least some of "a number of difficult problems..." can be understood by
(A) extrapolating from observable phenomenon
(B) anticipating the result of the collision of small bodies
(C) studying the rate of accretion on planets
(D) observing the internal process of planets
(S) discounting the dynamics of how orbits change over time
Explanation: The sentence, "This is fortunate…" describes how scientists can observe current events taking place in or regarding planets to learn more about "difficult problems of planetary origin.
(A) supports this idea best. 'Extrapolating' means taking information from one instance and applying it to an unknown instance (in this case, the early evolution of planets).
(B) is incorrect because anticipating, or trying to figure out, when small bodies in outer space will crash into each other, does not help shed light on the early formation of planets. Even if collisions were a part of the early formation of planet, (B) is focusing on future collisions.
(C) is a tempting answer. But scientists are relying on a host of planetary occurrences ("the dynamics of their orbital evolution, and the effect..."). While accretion is mentioned as an important process currently taking place, it doesn't explicitly say the rate of accretion is key to understanding "a number of difficult problems."
(D) is wrong. The "internal process of planets" is what makes it difficult for scientists to know about the early formation of planets.
(E) is wrong because the passage says that understand the orbit of planets can actually help scientists learn about the early formation of planets. Therefore, scientists would not "discount" information on the dynamics of orbits
The primary purpose of the passage is to
(A) present evidence that argues against a common misconception in the formation of planets
(B) undermine a claim regarding the role accretion plays in planetary evolution
(C) argue for the importance of using existing planetary conditions to understand prior cosmic occurrences
(D) underscore the importance of an astronomical process and describe ways in which we can understand this process
(E) discuss how, unless immediate action is taken, astronomers will squander an opportunity to better understand planetary formation
Explanation: The purpose of the passage is to discuss the importance, for those wanting to learn more about the evolution of our planets, of the "impact of small bodies." The passage specifically advocates using current processes to understand the historic processes.
(A) is wrong because there is no "common misconception" mentioned.
(B) is incorrect because accretion plays an important role
(C) is tempting because the passage does mention this. But the primary purpose is not only to discuss the importance of extrapolation but to assert the importance of the "impact of solid bodies" on the formation of our solar system.
(E) There is no talk in the passage about scientists potentially missing out on an opportunity.