There are Two Main Theories Concerning the Origin of the Lunar Craters

Reading Passage Question

There are two main theories concerning the origin of the lunar craters: one is that they were formed by the impact of meteorites, the other that they are due to some type of volcanic activity. According to the former theory, the large majority of the craters were formed during the early stages of the Moon’s development when, as seems possible, the number of meteoritic bodies moving in orbits similar to that of the Earth-Moon system was quite large. Since the Moon, unlike the Earth, possesses no atmosphere, such bodies would reach the lunar surface at a higher velocity than they would reach Earth. They also would not be affected by frictional burning such as they would undergo when plunging through the terrestrial atmosphere. When a large body strikes the lunar surface, it is not stopped at the moment of impact but penetrates to a depth that depends on its mass, radius, and impact velocity.

If we are to explain the very large craters on the assumption that several meteorites fell close together (in space, although not necessarily in time), this would imply that such craters should have uneven floors, not only indented to varying degrees by the several impacts but strewn with boulders and debris from the breakup of the meteorites themselves. Observation, however, suggests that the floors of large craters are smoother than can be accounted for by this theory unless there is some other mechanism whereby the floor becomes appreciably smoother following the impact.

One mechanism that has been suggested is that those meteorites that formed the craters fell on the lunar surface when the Moon was in a semiplastic condition or, if they fell after the lunar crust had solidified, that the impact itself would liquefy the surface rock sufficiently to force it to flow rather like lava. This liquefying of the rock at the moment of impact has also been put forward to explain the presence in some craters of a central mountain peak, since we know, from high-speed photography of drops falling into liquids, that a jet is formed in the center of an impact region.

There is, unfortunately, one very serious objection to this idea. When a body the size and shape of a meteorite strikes solid rock it is quite probable that no intermediate liquid phase of the surface rock is ever produced.

“There are two main theories concerning the origin of the lunar craters”- is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.

This GMAT Reading Comprehension consists of 6 comprehension questions. The GMAT Reading Comprehension questions are designed for the purpose of testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.

Solution and Explanation

1. According to the passage, one hypothesis proposed to explain the smoothness of the floors of large craters argues that the smoothness is a result of the

(A) disintegration of meteorites
(B) liquefying of surface rock
(C) numerous impacts of meteorites
(D) polar concentration of craters
(E) frictional burning of matter

2. Which of the following statements about the meteorite impact theory is most clearly supported by the information in the passage?

(A) It is more acceptable to scientists than is the volcanism theory. .
(B) It is able to explain some observed features of the Moon’s surface.
(C) It is one of several theories all of which seem equally tenable to scientists.
(D) Its importance is primarily historical. –
(E) It has been abandoned by most scientists.

3. The passage states that, in contrast to meteorites that enter the Earth’s atmosphere, meteorites striking the Moon are

(A) likely to be almost entirely burned up
(B) likely to fall close together
(C) likely to liquefy immediately
(D) able to create craters of widely varying diameters
(E) able to hit the surface at greater speeds

4. The author suggests that the theory that has been presented to explain the existence of central mountain peaks in some craters is based on

(A) the author's own observation of the behavior of lunar rock
(B) inadequate evaluations of the material structure of the lunar crust
(C) inference from an apparently similar situation
(D) conjectures with which the author agrees
(E) information that has become outdated

5. The author considers an explanation for the formation of very large lunar craters and then evaluates the explanation as

(A) confirmed by the characteristics of meteorites as they travel through space
(B) supported by observations concerning the liquefying of rocks
(C) incompatible, without further additions, with evidence of the smoothness of crater floors
(D) improbable because of a disparity with the known causes of analogous formations on Earth
(E) inconsistent, if unmodified, with the facts about the distribution of the large lunar craters

6. It can be inferred from the passage that unevenness in the floors of craters should have resulted from the fact that

(A) the meteorites that formed the craters had different masses of impact velocities ;
(B) the meteorites that formed the craters were all traveling at the same speed
(C) the meteorites that formed the craters all reached the Moon’s fur face at the same time
(D) when the meteorites struck the Moon, its surface was in a semiplastic condition
(E) when the meteorites struck the Moon, its surface was already uneven

Suggested GMAT Reading Comprehension Questions

• A One-Child Policy was Implemented in China in 1979
• Seeking a Competitive Advantage, Some Professional Service Firms
• On the surface, the Conquest of the Aztec Empire by Herman Cortes
• But Man is Not Destined to Vanish. He can be Killed, but he cannot be Destroyed, Because his Soul is Deathless and his Spirit is Irrepressible.
• When Literary Periods are Defined on the Basis of Men’s Writing, Women’s Writing Must be Forcibly Assimilated
• Behind Every Book Review There are Two Key Figures: A Book Review Editor and A Reviewer.
• Barbara Strozzi was a Singer and Composer of Madrigals, Aria
• During the Victorian Period, Women Writers were Measured Against A Social
• It Is Perhaps Not Surprising that Debate has Arisen Over Bioluminescence-Based Biotechnologies
• The Fact that Superior Service can Generate a Competitive Advantage
• The Origin of the Attempt to Distinguish Early from Modern Music
• The Phenomenon of College Basketball's Surging Popularity Remains a Challenge to Classify
• The United States Government has a Long-Standing Policy of Using Federal Funds to Keep Small Business Viable.
• A Recent Study has Provided Clues to Predator-Prey Dynamics in the Late Pleistocene Era.
• Even More Than Mountainside Slides of Mud or Snow, Naturally Occurring Forest Fires Promote the Survival of Aspen Trees.
• The Black Death, a Severe Epidemic that Ravaged Fourteenth Century Europe
• The System of Patent-Granting, Which Confers Temporary Monopolies for the Exploitation of New Technologies
• Ethnohistoric Documents from Sixteenth-Century Mexico Suggesting that Weaving and Cooking were the Most Common Productive Activities for Aztec Women
• Solar Ponds are Bodies of Water in Which Circulation is Incomplete and There is a Very High Salt Concentration that Increases with Depth
• Traditional Social Science Models of Class Groups in the United States are Based on Economic Status