Q17 - Samples from the floor

[lichenrachel]

Let's see if I understand answer A's argument correctly: Since there is no likely mechanism of contamination that permits contaminating only the deeper samples, if the samples are contaminated at all, they would all be contaminated by "old carbon", and the uppermost sample should be dated "later than present", hence not possible.

Am I right?

[bbirdwell]

Sounds pretty good to me. Essentially, all the samples would've been contaminated and thus be equally "old," or have conflicting dates. You got it...

[geverett]

This is somewhat odd Brian. I was stuck between A and D and chose A, because D would seem to refute the correlation of samples getting older the deeper they went. It would represent an inverse correlation as opposed to the direct correlation (the deeper the sample the older it is) cited in the stimulus. However, A seems kind of weak as well because while the critics attack the deeper samples date they don't say anything about the more recent sample. Yet A seems to assume that they agree with the dates assigned to the more recent samples. Thoughts?

[bbirdwell]

The skeptics claim that contamination made the samples appear too old.

(A) says "If that happened, then ALL the samples would have been affected, and therefore appeared toooooooo old." And we know this didn't happen, because there was a steady progression from the present backwards.

In other words, (A) says there's no way to have one really old, contaminated sample without screwing up all the others. And, based on the premises, we know that the others were not screwed up. See what I mean?

It's got to be our answer.

(D) You're correct. (D) points out that there was a bunk re-test. Careful about your task here. This choice SUPPORTS the skeptics! We want to refute them!

[geverett]

A ha! It just clicked. The samples date from the present to the oldest sample underground. If A were the case then the samples on the top dated to the present would then be dated older than the present which is impossible. Very good.

Not sure how answer choice D supports the skeptics though. It basically says that the samples were assigned the same or later date as the located above them which as I mentioned represents an inverse correlation of sorts.

[anjelica.grace]

What's wrong with (C)? Doesn't this choice deny the existence of any coal deposits that could have possibly contaminated the samples, thus weakening the skeptics' suggestion?

And I'm still not clear how the stimulus implies that the uppermost samples were not affected. Is that just assumed? What part of the stimulus would have led me to believe that the uppermost samples were not affected? I guess it's not that obvious to me.

[timmydoeslsat]

What's wrong with (C)? Doesn't this choice deny the existence of any coal deposits that could have possibly contaminated the samples, thus weakening the skeptics' suggestion?

And I'm still not clear how the stimulus implies that the uppermost samples were not affected. Is that just assumed? What part of the stimulus would have led me to believe that the uppermost samples were not affected? I guess it's not that obvious to me.

C would not have an impact on the skeptics because they would still claim that the old carbon came from the groundwater via coal deposits. Those coal deposits would still exist even if humans were not using it for fuel.

The reasoning used in choice A can be seen as follows. We know that the samples tested from the floor of this rock shelter were ones that were associated with human events. This rocks that were tested had a correlation between the age of the rock and its placement in the rock shelter.

We are told of the oldest rock being 19,650 years before the present and that there is one with beginning with the present. And we have other samples between those two samples that progress with age as we go deeper into the shelter.

A is telling us that if the groundwater contaminated the deeper rock, then the upper rock would have been contaminated too.

However, we know that the uppermost rock is from the present. So we know that the old carbon did not affect it. And if old carbon did not affect it, then we could use the contrapositive of this answer choice to end with "groundwater did not affect deep rock."

[anjelica.grace]

Also, can anyone explain how the re-test in (D) supports the skeptics, as Brian points out above?

Thank you for the response to my question. I now see why (A) is right and (C) is wrong. I appreciate the clarification.

[timmydoeslsat]

With choice D, its telling us that when the samples were retested using the carbon dating procedure again, this time not a single sample tested had a case where the above layer came from an earlier time. In other words, think of it this way:

We have a rock shelter floor _________ (1)
We have layers of rocks underneath ---- (2)
Here are more layers of rocks under it -- (3)

According to the stimulus, with the initial testing, we could expect something like this:

(1) 2000
(2) 1980
(3) 1970

What choice D is saying on the retesting of the samples is that, for example, layer (2) cannot be from an earlier time than layer (1).

So this ruins the above example that was consistent with the stimulus' initial testing.

This is saying that now layer 2 would be like this:

(2) 1980

No way could layer (1) be from the year 2000. We are told in D that no sample was from an earlier date than the one above it. 1980 is earlier than 2000, so there goes that idea.

[WaltGrace1983]

Am I oversimplifying this problem or missing something?

The conclusion, the skeptic's suggestion, is basically saying that the samples could have been contaminated by a very specific thing - "old carbon" from groundwater.

Thus, wouldn't (A) be the only one that is in anyway remotely relevant? We want to show why "old carbon" from groundwater couldn't make the tests appear how they did, correct? In that case, I see (B) - (E) as simply showing some really vague answer choices that have NOTHING to do with the test and why the test is either inaccurate/ineffective/etc.

(B) This is just saying that sometimes tests have been conducted that don't agree with the generally accepted hypotheses. So what? Sure, this could very slightly weaken the idea that the date of ~19,650 is too early by showing that there ARE instances in which tests don't add agree with what is frequently understood. However, it doesn't weaken the explanation given by the skeptics. It very slightly weakens their claim (a premise) but not the explanation (the conclusion).

(C) I honestly don't see how this is relevant at all. So they were or weren't using coal. So what? The argument doesn't hinge on using coal as fuel!

(D) This is just saying that another test was conducted and that test was bogus. Okay. This might also very slightly strengthen the skeptic's claim that 19,650 is not accurate by showing that the test used to achieve it was also not accurate. However, this hardly does anything to the argument regardless and, still, it does nothing to the explanation given by the skeptics.

(E) Again, it strengthens the claim of the skeptics a bit but not the explanation! Even if our task was to strengthen, we want to discuss the idea about "old carbon" and groundwater. This simply does not do that!

(A) is the only one that remotely discusses the skeptic's explanation. It talks directly about the groundwater. It weakens the skeptic's explanation by showing that their explanation is not sufficient.

[maryadkins]

Agree that relevance is a quick way to zoom in on (A), here, Walt, good thinking.

[513852276]

(D) This is just saying that another test was conducted and that test was bogus. Okay. This might also very slightly strengthen the skeptic's claim that 19,650 is not accurate by showing that the test used to achieve it was also not accurate. However, this hardly does anything to the argument regardless and, still, it does nothing to the explanation given by the skeptics.

I thought D strengthens the accuracy of the previous test, because D again demonstrates the date of samples is proportional to the depth from which the samples came. But what in dispute is the explanation of the result of previous test, not the accuracy of the previous test. Hence, we could eliminate D.

[roflcoptersoisoi]

What exactly is the argument core of this question?

[maryadkins]

I'd say the argument core is:

Premise: 19,000 or so years ago is too early as a date for the deepest sample because it's inconsistent with when humans migrated to North America.

Conclusion: The samples were contaminated by dissolved "old carbon" from groundwater.