#17 - Samples from the floor of a rock shelter in

[biskam]

I picked D but I have a feeling A is correct because it better targets the conclusion that the samples were contaminated. I want to understand though how the contamination affecting the uppermost sample would weaken the conclusion though...

I picked D because I thought it was confirming that the dates were in fact correct


Thank you!

[biskam]

Does A weaken because it throws off the inconsistency of the whole sequence... in effect messing up the premise and therefore the whole argument?

Upon second look, does D actually strengthen the conclusion by saying that the deeper samples might in fact be tainted? I might have read the phrasing wrong for "an earlier date..."

[Adam Tyson]

D hurts the original argument, the one that the skeptics don't like, by saying that the original results may have been wrong. When tested again, it appears that all the layers were just as young, if not younger, than every layer above it. That does nothing to weaken or strengthen the claim of the skeptics because it does nothing to address the issue of contaminated groundwater.

Answer A weakens the argument in favor of contamination by telling us that if that had happened, all of the layers, including the uppermost layer, would have to appear to be older than they are, and we know that this is not the case. The stimulus told us that the uppermost layer was dated consistent with it being from the present. If the percolating groundwater should have contaminated the uppermost layer and made it look older, and if it did not in fact look older than the present, then contaminated percolating groundwater could not have been at play here. Thus, the argument made by the skeptics that contaminated percolating groundwater had thrown the dates off is weakened.

I hope that helps clear it up for you some, biskam! Keep up the good work!

[Blueballoon5%]

Hello, lawschoolforme,

The skeptics are suggesting that only the bottom layers have been contaminated by "old carbon", thus making them appear older than they actually are. If D is true, that doesn't at all disprove the argument of the skeptics - D is basically saying that every layer is older than the one above it. D could suggest that the skeptics' argument is correct because of how much older the bottom-most layers are than the top-most. It may strengthen, but does not necessarily do so.

However, if A is true, there's no way that the bottom layers could have been contaminated without contaminating the upper layers also. That shatters the skeptics' argument that the bottom layers were affected in a way that the top layers were not.

Hope that helps,
Lucas Moreau
PowerScore

Hi Lucas! I hope you can help me. I can't find the reference in the stimulus that suggests the bottom layer being contaminated. Could you help me find that reference? Thank you!

[Vaidehi Joshi]

@Blueballoon5%

The stimulus doesn't DIRECTLY reference the bottom layer specifically being contaminated. Rather it says "The oldest and deepest sample"--i.e., the bottom layer--"was dated at 19,650 years..." and that "Skeptics view[ed] that date as too early and inconsistent with the accepted date of human migration into North America," and so for this reason, the skeptics "suggested that the samples could have been contaminated."

Thus, the stimulus seeks to EXPLAIN the dating (which is deemed inconsistent by skeptics) of the bottom layer, by suggesting contamination (of at least the bottom layer, but not necessarily ONLY the bottom layer--which is why correct answer (A) would weaken).

[andriana.caban]

Complete Question Explanation

Weaken. The correct answer choice is (A)

In this science-based stimulus, we learn about the carbon dating of rock shelters used by humans. While the test results show that human activity began about 20,000 years ago, "skeptics" believe that the tests may be inaccurately dating "old carbon" that percolating water may have carried to the site.

The question stem asks for the answer choice which weakens the skeptics' argument. The correct answer choice will likely either rule out the skeptics' hypothesis, or strengthen the case that the carbon-dating test is accurate.

Answer Choice (A): This is the correct answer choice. If, as this choice provides, percolating water would have affected all levels equally, then this rules out the skeptics' explanation.

Answer Choice (B): The fact that there have been some unsuccessful carbon dating efforts has no effect on the argument in the stimulus.

Answer Choice (C): The stimulus doesn't deal with the use of coal for fuel—just with the use of carbon content to estimate age.

Answer Choice (D): This potentially confusing answer offers the following: when they reattempted the carbon dating, the test did not show the deeper layers to be older. This suggests that on the second try, the test was inaccurate. This would not weaken the skeptics' argument—if anything, it might strengthen it.

Answer Choice (E): Some site has to have the oldest carbon; this does not automatically reduce the credibility of carbon dating.

Hi!

Thank you for providing an answer-choice by answer-choice explanation. Would it be possible to provide a summary of what each answer choice is saying? I particularly struggled in understanding what (E) meant.

[Brook Miscoski]

The wording in (E) is somewhat convoluted.

(E) is saying that the Pennsylvania site is the only place in North America that gave an older carbon date. The problem with (E) is that it doesn't help us understand whether the older date is from people or from coal contamination as discussed in the stimulus.

(A) suffers from bad wording as well. That choice is saying that if groundwater near the surface contaminated deeper buried water, the samples would already show that.

[LSAT2020]

I think the reason I am struggling with this is that I didn't fully understand the stimulus. To me, I thought the author was saying that skeptics believed that "old carbon" had contaminated all samples. I didn't realize that skeptics were specifically talking about the samples that were found in the deepest areas (i.e. the oldest samples). I have been re-reading the stimulus to try and see if there is any referential phrasing that I missed that would have indicated that the skeptics were specifically talking about the older samples, but I am struggling to find it. Would greatly appreciate your help.

[TZHUUMD22]

Hello Powerscore,

Where in the stimulus suggests that the bottom layer is contaminated whereas other layers are not?

Thanks!

Kokuu

[Paul Marsh]

Hi TZHUUMD22! This is a tricky question. The final sentence of the stimulus tells us that the skeptics believe the samples from the bottom-most layer have been contaminated, because the carbon date on the deepest samples are too old. The second sentence of the stimulus also tells us that the samples are "beginning with the present and going back in time"; in other words, the top layer is accurately dated as being from the present. Since the top layer accurately reflects the present while the skeptics think the bottom layer is wrong, we can infer that they believe the bottom layer is contaminated but not the topmost layer.

Hope that helps!