A vigorous debate in astronomy centers on an epoch in planetary histor

Question

A vigorous debate in astronomy centers on an epoch in planetary history that was first identified by analysis of rock samples obtained in lunar missions. Scientists discovered that the major craters on the Moon were created by a vigorous bombardment of debris approximately four billion years ago—the so-called late heavy bombardment (LHB). Projectiles from this bombardment that affected the Moon  should also have struck Earth , a likelihood with profound consequences for the history of Earth since, until the LHB ended, life could not have survived here.

Various theoretical approaches have been developed to account for both the evidence gleaned from samples of Moon rock collected during lunar explorations and the size and distribution of craters on the Moon. Since the sizes of LHB craters suggest they were formed by large bodies, some astronomers believe that the LHB was linked to the disintegration of an asteroid or comet orbiting the Sun. In this view, a large body broke apart and peppered the inner solar system with debris. Other scientists disagree and believe that the label “LHB” is in itself a misnomer. These researchers claim that a cataclysm is not necessary to explain the LHB evidence. They claim that the Moon’s evidence merely provides a view of the period concluding billions of years of a continuous, declining heavy bombardment throughout the inner solar system. According to them, the impacts from the latter part of the bombardment were so intense that they obliterated evidence of earlier impacts.  A third group  contends that the Moon’s evidence supports the view that the LHB was a sharply defined cataclysmic cratering period, but these scientists believe that because of its relatively brief duration, this cataclysm did not extend throughout the inner solar system. They hold that the LHB involved only the disintegration of a body within the EarthMoon system because the debris from such an event would have been swept up relatively quickly.

New support for the hypothesis that a late bombardment extended throughout the inner solar system has been found in evidence from the textural features and chemical makeup of a meteorite that has been found on Earth.  It seems to be a rare example of a Mars rock that made its way to Earth after being knocked from the surface of Mars.  The rock has recently been experimentally dated at about four billion years old, which means that, if the rock is indeed from Mars, it was knocked from the planet at about the same time that the Moon was experiencing the LHB. This tiny piece of evidence suggests that at least two planetary systems in the inner solar system experienced bombardment at the same time. However, to determine the pervasiveness of the LHB, scientists will need to locate many more such rocks and perhaps obtain surface samples from other planets in the inner solar system.    1 
 1. Which one of the following most accurately expresses the main point of the passage?

(A) The LHB is an intense meteorite bombardment that occurred about four billion years ago and is responsible for the cratering on the Moon and perhaps on other members of the inner solar system as well.
(B) Astronomers now believe that they may never collect enough evidence to determine the true nature of the LHB.
(C) If scientists continue to collect new clues at their current rate, the various LHB hypotheses can soon be evaluated and a clear picture will emerge.
(D) The Moon’s evidence shows that the LHB was linked to a small body that disintegrated while in solar orbit and sprayed the inner solar system with debris.
(E) New evidence has been found that favors the view that the LHB was widespread, but before competing theories of the LHB can be excluded, more evidence needs to be gathered.

2 
 2. The author’s attitude toward arguments that might be based on the evidence of the rock mentioned in the passage as being from Mars (lines 44–46:  Highlighted ) can most accurately be described as

(A) ambivalence because the theory of the rock’s migration to Earth is at once both appealing and difficult to believe
(B) caution because even if the claims concerning the rock’s origins can be proven, it is unwise to draw general conclusions without copious evidence
(C) skepticism because it seems unlikely that a rock could somehow make its way from Mars to Earth after being dislodged
(D) curiosity because many details of the rock’s interplanetary travel, its chemical analysis, and its dating analysis have not yet been published
(E) outright acceptance because the origins of the rock have been sufficiently corroborated

3 
 3. The author mentions that the LHB “should also have struck Earth” ( Highlighted ) primarily to

(A) support a particular theory of the extent of the LHB
(B) question the lack of LHB evidence found on Earth
(C) advocate certain scientific models for the origins of life on Earth
(D) provide a reason why scientists are interested in studying the LHB
(E) introduce additional support for the dating of the LHB

4 
 4. The author implies that all theoretical approaches to the LHB would agree on which one of the following?

(A) the approximate duration of the LHB
(B) the origin of the debris involved in the LHB
(C) the idea that cratering decreased significantly after the LHB
(D) the idea that the LHB destroyed the life that existed on Earth four billion years ago
(E) the approximate amount of debris involved in the LHB

5 
 5. According to the passage, the third group of scientists ( Highlighted ) believes that the LHB

(A) affected only the Moon
(B) was so brief that its extent had to be fairly localized
(C) consisted of so little debris that it was absorbed quickly by the planets in the inner solar system
(D) occurred more recently than four billion years ago
(E) may have lasted a long time, but all its debris remained within the Earth-Moon system

6 
 6. Which one of the following, if true, would lend the most support to the view that the LHB was limited to Earth and the Moon?

(A) An extensive survey of craters on Mars shows very little evidence for an increase in the intensity of projectiles striking Mars during the period from three billion to five billion years ago.
(B) Scientists discover another meteorite on Earth that they conclude had been knocked from the surface of the Moon during the LHB.
(C) A re-analysis of Moon rocks reveals that several originated on Earth during the LHB.
(D) Based on further testing, scientists conclude that the rock believed to have originated on Mars actually originated on the Moon.
(E) Excavations on both Earth and the Moon yield evidence that the LHB concluded billions of years of heavy bombardment.

LSAT Official PrepTest 51

Sajjad1994 · Answer

Explanation

1. Which one of the following most accurately expresses the main point of the passage?

Explanation

Roadmap:

Para 1:  Moon mission found ev of LHB causing craters on Moon. Should have affected Earth as well as Moon.

Para 2:  3 theories re: cause and extent of LHB

Para 3:  New ev (rock from Mars found on Earth) supports LHB affected inner solar system. Need more ev to confirm.

Our roadmap of  Paragraph 3  sets out the author’s main idea quite nicely: new evidence supports the theory that LBH was widespread throughout the inner solar system, but we need more evidence to be sure. That’s  (E) .

(A)  is a nice summary of paragraph 1, but we are looking for an answer choice that justifies everything in the passage, not just part of the passage.

(B)  distorts the author’s point—according to the author, additional evidence is needed to determine the exact nature of the LHB, but the author never expresses an opinion as to how likely it is that additional evidence will be found.

The author never discusses the rate at which evidence relating to the LBH is being found, so  (C)  is outside the scope of the passage.

In ( lines 19–21:  In this view, a large body broke apart and peppered the inner solar system with debris.), the author notes that the sizes of LHB craters suggest they were formed by large bodies, so  (D)  is a 180.

Answer: E

Sajjad1994 · Answer

Explanation

3. The author mentions that the LHB “should also have struck Earth” (Highlighted) primarily to

Difficulty Level:   Hard

Explanation

The author’s reason for noting that the LHB  “should”  have affected Earth may not be immediately apparent to many students. The detail is consistent with all three theories about the LHB, so we can rule out (A).

The author never suggests that there is an unexpected or significant lack of LHB evidence on Earth, and at the end of the passage, the author discusses an important piece of evidence that was found on Earth. Rule out (B).

The author never advocates any scientific model for the origins of life on Earth.  (C)  is, therefore, another wrong answer choice.

The author never explicitly states why the probable effects of the LHB on Earth are important, but the author’s statement at the end of paragraph 1, that life on earth Earth could not have begun until after the LHB had ended would provide a compelling reason for studying the LHB. So  (D)  is a keeper.

Consideration of  (E)  confirms that  (D)  is correct—the author never draws or suggests a connection between the supposed effect LBH had on Earth with the dating of the LBH.

Answer: D

Sajjad1994 · Answer

Explanation

6. Which one of the following, if true, would lend the most support to the view that the LHB was limited to Earth and the Moon?

Difficulty Level:   750

Explanation

The right answer choice may not definitively prove that the LHB was limited to the Earth-Moon system, but it will make that claim somewhat more likely to be true. The Mars rock found on Earth was the only evidence offered in support of the theory that the effects of the LHB extended beyond the Earth-Moon system. If exploration of Mars suggests that there was not an increase in the intensity of projectiles hitting that planet during the time period the LHB is believed to have occurred, then the finding of a Mars rock on Earth no longer suggests that the LHB must have affected Mars as well as the Earth-Moon system.

Each of the remaining answer choices is consistent with the LHB either being limited to the Earth-Moon system, or extending beyond the Earth-Moon system, and so they do not strengthen our argument.

Option (D)  is incorrect because it does not support the view that the Late Heavy Bombardment (LHB) was limited to Earth and the Moon. In fact, it suggests the opposite. Let's analyze why:

Option (D) states: "Based on further testing, scientists conclude that the rock believed to have originated on Mars actually originated on the Moon."

If this were true, it would mean that the rock, previously thought to be from Mars and potentially evidence of a separate bombardment event on Mars concurrent with the LHB on the Moon, is actually from the Moon. This would imply that the LHB extended beyond the Moon and also affected Mars, thus contradicting the idea that the LHB was limited to Earth and the Moon.

The question asks for the option that would lend the most support to the view that the LHB was limited to Earth and the Moon. In contrast,  option (D)  suggests that the LHB extended to Mars as well, making it inconsistent with the desired viewpoint. Therefore,  option (D)  is incorrect in this context.

Answer: A

Sajjad1994 · Answer

Explanation

2. The author’s attitude toward arguments that might be based on the evidence of the rock mentioned in the passage as being from Mars (lines 44–46: Highlighted) can most accurately be described as

Difficulty Level:   700

Explanation

In  paragraph 3 , the author describes new evidence that suggests that the effects of the LHB went beyond the Earth-Moon system. The keyword  “however”  tells us that the author does not believe that this new evidence settles the debate that is central to this passage. The author would like to see many more rocks like the Mars rock described at the beginning of the paragraph.

(B)  captures the author’s concern that much more evidence is needed to come to any definitive conclusions. A vertical scan of the verbs used in the other answer choices shows how those choices miss the mark: the author is not  “ambivalent”  about the evidence, as  (A)  says, nor is she  “skeptical”  as in  (C) . The paragraph provides the details that  (D)  proposes the author is still  “curious”  about, and (E)’s suggestion that the author completely  “accepts”  the arguments made based upon the Mars rock ignores the author’s reservations expressed in the last sentence of the paragraph. All of these answer choices are 180s.

Answer: B

Saupayan · Answer

I am sorry but I am not convinced with this explanation for D. The passage tells us LHB could either be localized (to Earth-Moon area) or spread out (inner Solar System). The rock that we have found and thought to be from Mars lends support to the later hypothesis. Why? Because it suggests LHB is more spread out than just the Earth-Moon region. It is not evidence for another totally different bombardment. It is evidence for LHB.
So if that evidence turns out to be incorrect, then our hypothesis will be called into question. Hence, weakener.
What am I missing here?

Sajjad1994 · Answer

Option (D)  states that scientists conclude, based on further testing, that the rock believed to have originated on Mars actually originated on the Moon. If this were true, it would weaken the argument that the LHB extended throughout the inner solar system. However, the key issue here is that  option (D)  doesn't necessarily provide direct support for the hypothesis that the LHB was limited to Earth and the Moon. It only presents a scenario where a piece of evidence (the rock believed to be from Mars) is found to be incorrect. This doesn't necessarily prove that the LHB was localized, as there could still be other evidence supporting the idea of a widespread bombardment.

On the other hand,  option (A)  directly addresses the issue of the intensity of projectiles striking Mars during the relevant time period. If it is found that there was very little evidence for an increase in the intensity of projectiles striking Mars during the period of the LHB, it suggests that the intense bombardment was not a widespread phenomenon affecting multiple planets in the inner solar system. This would lend more support to the idea that the LHB was limited to Earth and the Moon.

While both  options (A)  and  (D)  address evidence that could potentially weaken the hypothesis of a widespread LHB,  option (A)  provides more direct support for the specific view that the LHB was limited to Earth and the Moon, making it a stronger choice according to the information provided in the passage.

Saupayan · Answer

I agree with what you said. However, extending your reasoning for D, option A doesn't necessarily provide direct support for the hypothesis that the LHB was limited to Earth and the Moon. At best, it suggests Mars wasn't involved. What about Mercury and Venus? What if Mars was spared just because in that very short duration of LHB, it was just never in the right position and planets farther away were infact bombarded?

callingTardis · Answer

maybe this will help I agree that (D) is attractive. However, the discovery of an alternate explanation for the origin of the Mars rock would not serve to disprove other theories that are not restricted to the Earth-Moon system. Mars could still have been involved, even if this one particular rock actually originated in the Moon. By comparison (A) essentially disproves the notion that Mars was involved in the LHB, which better supports the theory that the LHB was limited to the Earth-Moon system. source: powerscore lsat https://forum.powerscore.com/viewtopic. ... 0that%20(D)%20is%20attractive,limited%20to%20the%20Earth%2DMoon%20system.

Sajjad1994 · Answer

Explanation

4. The author implies that all theoretical approaches to the LHB would agree on which one of the following?

Explanation

When you are asked to identify a point of agreement (or point at issue) between different theories, first research and summarize the theories you are asked to compare.
 
What are the three theories?  1)  The LHB was linked to the cataclysmic disintegration of a large body, such as an asteroid or comet, which spread debris throughout the inner solar system.  2)  The LHB was a long-term process, not part of a cataclysmic event, affecting the inner solar system.  3)  The LHB was a cataclysmic event, but only affected the Earth-Moon system. Now we can evaluate the answer choices, asking ourselves with respect to each answer choice whether the answer choice is consistent with each of the 3 theories.

Theories 1 and 3 suggest that the LHB was of relatively short duration, but theory Theory 2 suggests that what is called the LHB was the end of billions of years of declining bombardment. Eliminate    (A) .

Theories 1 and 3 suggest that the LHB was the result of a cataclysmic disintegration of a large body such as an asteroid or comet. Theory 2 suggests that the LHB was not the result of any cataclysmic event. Eliminate    (B)  .

Theories 1 and 3 describe LHB as  “cataclysmic,”  and Theory 2 describes LHB as  “the period concluding billions of years of a continuous, declining heavy bombardment.”     (C)   is our good answer choice.

For the record, none of the theories suggests that there was life on Earth prior to or at the time of the LHB   (D) , and none of the theories attempts to quantify the  amount of debris involved in the LHB.   (E) .

Answer: C

Sajjad1994 · Answer

Explanation

5. According to the passage, the third group of scientists (   Highlighted   ) believes that the LHB

Explanation

The question directs us to the third group of scientists, and even gives us a line reference. Those scientists believed that the LHB was cataclysmic, and was limited to the Earth-Moon system because of its  “relatively brief duration.”  Sounds a lot like correct answer  choice (B).

(A)  is half right, half wrong. According to the third group of scientists, both the Earth and Moon were affected by the LHB.

(C)  goes beyond the scope of the passage, none of the scientists attempted to estimate the amount of debris involved in the LHB.

(D)  The author never suggests that there is a dispute between any of the scientists regarding the dating of the LHB as having occurred about 4 billion years ago.

(E)  is another half right, half wrong answer. The scientists referenced in the question argue that the debris remained within the Earth-Moon system, but that it was an event of relatively short duration.

Answer: B

A vigorous debate in astronomy centers on an epoch in planetary histor

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A vigorous debate in astronomy centers on an epoch in planetary histor

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