Logical Reasoning

PT6 · S3 · Q17 Samples from the floor of a rock

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Samples from the floor of a rock shelter in Pennsylvania were dated by analyzing the carbon they contained.

Skeptics' Suggestion

The sample dates could be contaminated by "old carbon" from percolating groundwater, leading to earlier-than-expected results.

Evidence

Skeptics believe these dates are too early and suggest contamination from nearby coal deposits as the cause.

Evaluate

Curious Fact: Why are the samples dated much earlier than the accepted timeline for human migration into North America?

Implied Explanation: The samples are truly as old as dated, suggesting earlier human presence.

Skeptics' Alternate Explanation: Contamination from old carbon carried by groundwater affected the sample dates, making them appear older than they are.

We need to counter the skeptics' suggestion of contamination to strengthen the claim that the carbon-dating results are accurate and untainted.

Goal

Let's find an answer that argues against the possibility of contamination affecting the sample dates, or that proposes an alternate explanation for why these sample dates are earlier than we would have thought we'd find humans in Pennsylvania.

17.

Which of the following considerations, if true, argues most strongly against the suggestion of the skeptics?

  1. Correct

    No likely mechanism of contamination

    Why this is right

    This makes the skeptics explanation seem implausible by pointing out that any contamination from groundwater should have logically affected all samples, not just deeper ones. Since the uppermost samples don't have the same "contaminated" date as the lower samples, it doesn't look like the lower samples were contaminated.

    Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

    71% picked this

  2. Not every application of the

    Strengthens (if anything)

    This is an incredibly weak idea, so very likely to be correct on Str/Wkn/Pdx. Additionally, saying that "at least one application of carbon-dating has NOT led to acceptable results" would help the skeptics argue that this suspicious carbon dated sample is wrong.

    2% picked this

  3. There is no evidence that

    No Impact

    The skeptics' contamination theory doesn't depend on using coal for fuel, but rather on natural soil/groundwater interactions, so this choice doesn't effectively counteract the contamination claim.

    11% picked this

  4. No sample in the series,

    No Impact

    Answer D highlights that no deeper sample is older than one above it, supporting the data's internal consistency but doing little to address whether groundwater could have made the bottom layer's date look earlier than it really was.

    13% picked this

  5. No North American site besides

    Opposite Impact (strengthens)

    This would help the skeptics argue that this oldest dated sample must be screwed up in some way, since we've never seen a comparably ancient sample elsewhere in North America.

    4% picked this

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