First, it's important to understand what information the question stem gives us. It says that rock samples from the floor of a shelter are associated with human activities. The deeper the samples were taken from the floor, the older the human activity associated with it. It also says that the most recent sample is from the present, and therefore coincides with recent human activity – in the present.
The Skeptics, however, are arguing that the date of the deepest layer is not accurate. They claim that it could have been contaminated by water containing "older" carbon, thereby making it seem older than it is.
Answer (A) is the correct answer because it claims that if the deepest layer were to be contaminated, so would all the layers above it. We know that the most recent layer is the surface itself, coinciding with activities from the PRESENT. If these activities are from the present, they certainly can't be dated incorrectly. Thus, (A) weakens the Skeptics' argument.
This question stem was definitely harder to grasp that a lot of others, but it would be worth it to take a step back when you're struggling to understand it/the right answer. Every time I've gotten the wrong answer and didn't know why, I tried to map out the conclusion and premises of the argument before even looking at the message boards – it's a much better way to learn! (The message boards are great when I still can't figure it out, lol).
ZhenzhenOctober 25, 2020
Thanks for the explanation Isaak. It makes a lot of sense.
AlejandroJune 9, 2024
But the stimulus does NOT say that the skeptics think the deeper sample is contaminated. It says they think the sample*s* were contaminated by "old carbon." Which I read to mean that their argument is that every sample that was collected was contaminated. If that is the case, A doesn't seem to be the answer at all and was why I immediately ruled it out. If the skeptics argue that the sample*s* are contaminated then it seems they would agree with (A).
Emil-KunkinJune 12, 2024
As to the point about samples, the nearest antecedent use of that word is specifically referring to the oldest and deepest samples- and since we are told that the skeptics are only questioning the oldest dates, I think we can safely assume that the samples they are talking about are those oldest and deepest ones mentioned in the previous sentence.
However as to the bigger point I mostly agree with you. We are never actually told the skeptics accept the other dating, only that they question the oldest dating. That said I think there is still a strong argument as to how it weakens: A would mean that the skeptics would have to commit themselves to a view that all the samples are likely questionable at best. However, this position is much more extreme than the one they actually took. It does cast some doubt on a position if you can show that it commits the author to an even more extreme position. It certainly doesn't kill the argument, but it does make me less likely to accept it, and that's what a weakener should be. Furthermore the fact that they only attacked the oldest date does give us some hint that they are not likely to actually contest the more recent date.
