Commentator: Many people argue that the release of chlorofluorocarbons into the atmosphere is harming humans by dam...

Naz on December 16, 2013

This argument does not contain sufficient and necessary sentences, so we cannot diagram it. You are correct to identify this as a cause and effect weaken argument. The commentator is trying to weaken the claim that "the release of chlorofluorocarbons into the atmosphere is harming humans by damaging the ozone layer, thus allowing increased amount of ultraviolet radiation to reach Earth." The claim states: damage to the ozone layer causes harm to humans. You are correct to point out that the commentator, in an attempt to weaken this cause and effect argument, is trying to show cause without effect, i.e. "300,000 years ago a supernova greatly damaged the ozone layer, with no significant effect on our earliest ancestors." Great work!

The commentator concludes that because "the supernova's disruption was much greater than the estimated effect of chlorofluorocarbons today, there is no reason to think that these chemicals in the atmosphere harm humans in this way."

Thus, answer choice (C) is the correct answer because, if true, it would most seriously weaken the commentator's argument. If it were true that our "earliest ancestors possessed genetic characteristics making them more resistant than we are to the harmful effects of ultraviolet radiation," then the commentator's "cause without effect" defense no longer holds. Our earliest ancestors possessed an extra protection against the ultraviolet radiation that we do not possess. Thus, though the damage to the ozone layer 300,000 years ago posed no significant effect on our earliest ancestors, that does not mean it wouldn't pose significant harm to us, since we do not have the genetic characteristics that made them more resistant to the radiation.

Hope that was helpful! Please let us know if you have any other questions.

esther on July 30, 2018

why cant the answer be D

ulino23 on March 6, 2019

Why is E incorrect??

Ravi on March 12, 2019

@esther and @ulino23,

Great questions.

(D) says, "The ozone layer regenerates at a slow rate, barring
counteractive processes."

(D) tells us that the ozone repairs itself slowly. However, the author
of the passage would be o.k. with accepting this because the author
claims that additional amounts of UV light don't harm humans because
there was no significant effect on our earliest ancestors when the
supernova damaged the ozone layer. Thus, (D) doesn't weaken the
author's claim that increased amounts of UV radiation don't harm
humans.

(E) says, "Scientists have discovered that genetic changes occurred in
our ancestors during the period in which the supernova affected
Earth."

The problem with (E) is that we don't know what these genetic changes
were and what caused them. It's possible that they had nothing to do
with the supernova. (E) is baiting us into thinking that correlation
proves causation, and as we know, it doesn't. What if the genetic
changes were an increase in brain size, making our ancestors smarter?
(E) is way too vague and doesn't weaken the author's argument.

Does this make sense? Let us know if you have any questions!