- PowerScore Staff
- Posts: 8950
- Joined: Feb 02, 2011
- Mon Mar 06, 2017 12:00 am
#36254
Complete Question Explanation
Weaken. The correct answer choice is (C)
The commentator’s argument uses the familiar construction where a view is presented (“Many
people argue that…”) and then the author presents contrary information that leads to the main point
that the view is incorrect. Remember, by knowing some of the common argument forms that appear
on the LSAT, you can more quickly grasp the gist of the author’s argument, and thereby complete
questions more quickly.
In the last sentence of the stimulus, the commentator concludes that there is no reason to believe
that chlorofl uorocarbons harm humans by damaging the ozone layer enough to allow increased
ultraviolet radiation to reach Earth. The commentator reaches this conclusion by using the premise
that a supernova 300,000 years ago disrupted the ozone layer in a more signifi cant manner than the
estimated effect of chlorofl uorocarbons today, but that disruption occurred without signifi cantly
affecting our earliest ancestors.
The conclusion drawn by the commentator is questionable. Most importantly, remember that in
questions involving a lengthy time period, the author almost always makes the assumption that all
things remain the same. In this case, the commentator has assumed that a comparison to ancestors
from 300,000 years ago is meaningful because those ancestors are fundamentally similar to humans
today. Of course, this assumption is fl awed because those ancestors may have been different from us
in ways that protected them from increased ultraviolet radiation. Or perhaps they did not live all that
long and that fact prevented them from experiencing the long-term effects of increased ultraviolet
radiation exposure. In any case, the “continuity of history” assumption is an important one for you to
recognize when it appears in an LSAT question (and when it does appear, always look for an answer
that addresses that assumption).
There are other issues with the commentator’s conclusion, such as whether an effect must be
signifi cant to be harmful, and whether the estimations are completely accurate. Regardless, it should
be clear that the commentator is using a very limited amount of evidence to draw a conclusion that
is extremely questionable. Since you are asked to weaken the argument, you should search for a
response that provides evidence that questions the commentator’s conclusion.
Answer choice (A): This choice has to do with the frequency of categories of events, but the
commentator made a comparison between the impact of two specififi c events. The commentator
never attempted to generalize from these two events to a conclusion about whether terrestrial or
extraterrestrial infl uences were overall more frequent (or important), so this choice does not weaken
the argument.
Answer choice (B): This answer choice does nothing to the argument, because we cannot be sure
whether the estimation of the effect of chlorofl uorocarbons took into account natural processes
such as volcanoes. If it did not, this choice might actually strengthen the conclusion by making the
chlorofl uorocarbons even less important.
Answer choice (C): This is the correct answer choice. Remember that one of the assumptions of
the argument was that humans today are comparable to human ancestors who lived 300,000 years
ago. This response shows that they are not the same with respect to a critical feature. Specifi cally,
the answer choice establishes that our earliest ancestors were more resistant to the harmful effects
of ultraviolet radiation than we are today. If the humans of 300,000 years ago were more resistant
than humans today, then it may very well be that the chemicals in the atmosphere today could have a
harmful effect. Consequently, this answer choice weakens the commentator’s argument.
Answer choice (D): You may have chosen this response by concluding that recovery from a
supernova would occur more quickly than recovery from chlorofl uorocarbon damage because
chemicals persist in the atmosphere. However, even if that is true, the commentator was discussing
the current harm to humans, and not how harmful chlorofl uorocarbons might become, or might prove
to be over the long run. This answer choice is off-topic and incorrect.
Answer choice (E): This is the most frequently selected incorrect answer. This answer choice does
not weaken the author’s argument because it does not establish the nature of the genetic changes.
You should not assume that the changes were the result of the increased ultraviolet radiation, that the
changes had a harmful effect, or that the changes resulted in decreased genetic protection for today’s
humans. Because this answer offers no concrete information, this answer choice cannot weaken the
argument.
Weaken. The correct answer choice is (C)
The commentator’s argument uses the familiar construction where a view is presented (“Many
people argue that…”) and then the author presents contrary information that leads to the main point
that the view is incorrect. Remember, by knowing some of the common argument forms that appear
on the LSAT, you can more quickly grasp the gist of the author’s argument, and thereby complete
questions more quickly.
In the last sentence of the stimulus, the commentator concludes that there is no reason to believe
that chlorofl uorocarbons harm humans by damaging the ozone layer enough to allow increased
ultraviolet radiation to reach Earth. The commentator reaches this conclusion by using the premise
that a supernova 300,000 years ago disrupted the ozone layer in a more signifi cant manner than the
estimated effect of chlorofl uorocarbons today, but that disruption occurred without signifi cantly
affecting our earliest ancestors.
The conclusion drawn by the commentator is questionable. Most importantly, remember that in
questions involving a lengthy time period, the author almost always makes the assumption that all
things remain the same. In this case, the commentator has assumed that a comparison to ancestors
from 300,000 years ago is meaningful because those ancestors are fundamentally similar to humans
today. Of course, this assumption is fl awed because those ancestors may have been different from us
in ways that protected them from increased ultraviolet radiation. Or perhaps they did not live all that
long and that fact prevented them from experiencing the long-term effects of increased ultraviolet
radiation exposure. In any case, the “continuity of history” assumption is an important one for you to
recognize when it appears in an LSAT question (and when it does appear, always look for an answer
that addresses that assumption).
There are other issues with the commentator’s conclusion, such as whether an effect must be
signifi cant to be harmful, and whether the estimations are completely accurate. Regardless, it should
be clear that the commentator is using a very limited amount of evidence to draw a conclusion that
is extremely questionable. Since you are asked to weaken the argument, you should search for a
response that provides evidence that questions the commentator’s conclusion.
Answer choice (A): This choice has to do with the frequency of categories of events, but the
commentator made a comparison between the impact of two specififi c events. The commentator
never attempted to generalize from these two events to a conclusion about whether terrestrial or
extraterrestrial infl uences were overall more frequent (or important), so this choice does not weaken
the argument.
Answer choice (B): This answer choice does nothing to the argument, because we cannot be sure
whether the estimation of the effect of chlorofl uorocarbons took into account natural processes
such as volcanoes. If it did not, this choice might actually strengthen the conclusion by making the
chlorofl uorocarbons even less important.
Answer choice (C): This is the correct answer choice. Remember that one of the assumptions of
the argument was that humans today are comparable to human ancestors who lived 300,000 years
ago. This response shows that they are not the same with respect to a critical feature. Specifi cally,
the answer choice establishes that our earliest ancestors were more resistant to the harmful effects
of ultraviolet radiation than we are today. If the humans of 300,000 years ago were more resistant
than humans today, then it may very well be that the chemicals in the atmosphere today could have a
harmful effect. Consequently, this answer choice weakens the commentator’s argument.
Answer choice (D): You may have chosen this response by concluding that recovery from a
supernova would occur more quickly than recovery from chlorofl uorocarbon damage because
chemicals persist in the atmosphere. However, even if that is true, the commentator was discussing
the current harm to humans, and not how harmful chlorofl uorocarbons might become, or might prove
to be over the long run. This answer choice is off-topic and incorrect.
Answer choice (E): This is the most frequently selected incorrect answer. This answer choice does
not weaken the author’s argument because it does not establish the nature of the genetic changes.
You should not assume that the changes were the result of the increased ultraviolet radiation, that the
changes had a harmful effect, or that the changes resulted in decreased genetic protection for today’s
humans. Because this answer offers no concrete information, this answer choice cannot weaken the
argument.