idinuv wrote:
Source :
GMATPrep Default Exam PackThis passage was excerpted from material published in 1996.
When a large body strikes a planet or moon, material is ejected, thereby creating a hole in the planet and a local deficit of mass. This deficit shows up as a gravity anomaly: the removal of material that has been ejected to make the hole results in an area in slightly lower gravity than surrounding areas. One would therefore expect that all of the large multi-ring impact basins on the surface of earth's moon would show such negative gravity anomalies, since they are, essentially, large holes in lunar surface. Yet data collected in 1994 by the Clementine spacecraft show that many of these Clementine basins have no anomalously low gravity and some even have anomalously high gravity. Scientists speculate that early in lunar history, when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin. Later, however, as moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such gravitational compensation probably would not occur: the outer layer of moon is too cold and stiff.
1. According to the passage, the
gravitational compensation referred to in the highlighted text is caused by which of the following?
(A) A deficit of mass resulting from the creation of hole in lunar surface
(B) The presence of material from the impactor in the debris created by its impact
(C) The gradual cooling and stiffening of the Moon's outer surface
(D) The ejection of massive amounts of debris from the moon's crust
(E) The rapid upwelling of material from the lunar mantle
2. The passage suggests that if the
scientists mentioned in the highlighted text are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably
(A) were not formed early in the Moon's history
(B) were not formed by the massive ejection of crustal debris
(C) are closely surrounded by other impact basins with anomalously low gravity
(D) were created by the impact of multiple large impactors
(E) were formed when the moon was relatively elastic
3. The passage is primarily concerned with
(A) analyzing data from a 1994 exploration of lunar surface
(B) reconciling two opposing theories about the origin of lunar impact basins
(C) presenting a possible explanation of a puzzling finding about lunar impact basins
(D) discussing how impact basins on the Moon's surface are formed
(E) examining the claim that the moon's impact basins show negative gravity anomalies
Kindly provide explanations for 3rd Question. I selected E.
4 mins 46 seconds : including 2 min 10 sec reading
Divide passage in 2 paras When a large body strikes a planet or moon, material is ejected, thereby creating a hole in the planet and a local deficit of mass. This deficit shows up as a gravity anomaly: the removal of material that has been ejected to make the hole results in an area in slightly lower gravity than surrounding areas. One would therefore expect that all of the large multi-ring impact basins on the surface of earth's moon would show such negative gravity anomalies, since they are, essentially, large holes in lunar surface. Yet data collected in 1994 by the Clementine spacecraft show that many of these Clementine basins have no anomalously low gravity and some even have anomalously high gravity.
(summary - An expected consequence of a phenomenon is challenged by recent findings.... prethinking - author may try to explain why such data was otained or he may try to put another thesis to explain the data obtained ...) Scientists speculate that early in lunar history, when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin. Later, however, as moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such
gravitational compensation probably would not occur: the outer layer of moon is too cold and stiff.
(summary - an explanation to the unexpected findings... )TOPIC - Lunar deficit.
PURPOSE- to explain the unexpected finding about a phenomenon...
Main idea - There is a possibilty that the unexpected finding may be the result of upwelling of mass from moon.1. According to the passage, the
gravitational compensation referred to in the highlighted text is caused by which of the following?
According to the passage, the
gravitational compensation referred to in the highlighted text is caused by which of the following?
Relevant text - when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin. Later, however, as moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such
gravitational compensation probably would not occur
- When there is a hole ( deficit) , mantle rises up , and fills the void ..this phenomenon is COMPENSATION...
What causes the compensation?? - the rising of mantle...(A) A deficit of mass resulting from the creation of hole in lunar surface
- this does not cause anything. This AC is telling about what happen when IMPACTORS collide...
(B) The presence of material from the impactor in the debris created by its impact
- The presence of material does not cause anything.. infact when the impactor makes an impact and the released debris has this material ...OOS
(C) The gradual cooling and stiffening of the Moon's outer surface
-This explains why compensation
MAY not happen now
(D) The ejection of massive amounts of debris from the moon's crust
-ejection will result in debris in space... nothing else
(E) The rapid upwelling of material from the lunar mantle
- CORRECT ANSWER - rapid ( almost immediately - from passage) upwelling - see explanation...2. The passage suggests that if the
scientists mentioned in the highlighted text are correct in their speculations, the large multi-ringmpact basins on the Moon with the most significant negative gravity anomalies probably
The passage suggests that if the
scientists mentioned in the highlighted text are correct in their speculations, the large multi-ring impact basins on the Moon with the most significant negative gravity anomalies probably
-relevant text -
Scientists speculate that early in lunar history, when large impactors struck the moon's surface, causing millions of cubic kilometers of crustal debris to be ejected, denser material from the moon's mantle rose up beneath the impactors almost immediately, compensating for the ejected material and thus leaving no gravity anomaly in the resulting basin. Later, however, as moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such
gravitational compensation probably would not occur: the outer layer of moon is too cold and stiff.
speculation - impact >> deficit (void) >> mantle rises up >> NO GRAVITATIONAL ANAMOLY ...
so if this process is true what will be true??(A) were not formed early in the Moon's history- CORRECT
Look carefully at the end of 2nd passage ( Later, however, as moon grew cooler and less elastic, rebound from large impactors would have been only partial and incomplete. Thus today such gravitational compensation probably would not occur: the outer layer of moon is too cold and stiff.) .. so this means[color=#ff0000] NOW MOON IS TOO STIFF AND COLD and hence gravitational compensation would not have happened .. if it would have happened it would be comoensated with mantle.. LOOK AT THE TIME PERIODS ... NOW - no compensation .. Earlier time - compensation possible... now the Q says there IS A LARGE DEFICIT ... so if there is a large deficit NOW then it wldnt have formed earlier , because if it did there would be compensation.. but now the moon is stiff and hence no compensation..[/color]
(B) were not formed by the massive ejection of crustal debris-
- There are many ways to form a deficit ... passage never says "only" impactors create
(C) are closely surrounded by other impact basins with anomalously low gravity- OOS
- NO IDEA
(D) were created by the impact of multiple large impactors
- There are many ways to form a deficit ... passage never says "only" impactors create
(E) were formed when the moon was relatively elastic
- MOST COMMON WRONG AC - why we fall for this AC?? because we read only the last part and think that now the moon is stiff and cold so deficits would not have formed but earlier, the moon was elastic so deficit was possible ... SO basically we just messed up the entire para .. the elasticity explanation is for GRAVITATIONAL COMPENSATION and not possible deficit.... the deficits can form all the time .. it is the compensation that cannot