Logical reasoning PrepTest 107 · Section 3 · Question 19

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Bizarro Strengthen with Necessary Premise

Stimulus Summary:
Old theory - A meteorite in a certain region killed off plants/animals in the Mesozoic

New evidence - When molten rocks crystallize, they take on Earth's polarity. The rocks at the site of the impact don't match the polarity at the time of the extinction.
Conclusion - The meteorite that formed that crater didn't cause the extinctions

Answer Anticipation:
This answer has three elements to it that we can look at to see if there are assumptions related to them.

First, the argument is causal. However, it concludes that a causal relationship isn't present—the meteorite didn't cause the mass extinctions. This is because the timeline doesn't match up—at least, according to the rock polarity.

Which brings us to the next two elements, which are related and lead to the flaw in this argument. For causality to make sense, the cause has to happen before the effect, but not so far away from it that there's no way they could be linked. Here, the timeline is key to the Professor's argument, but she doesn't establish it directly—she establishes by proxy by looking at the polarity of the rocks at the site.

Since she shows that the rocks at the impact site recrystallized at a different time than the mass extinctions happened, she concludes that the meteorite couldn't have caused the extinctions. As such, she's assuming that her proxy and timeline make sense. Any answer that connects these concepts will serve as a necessary assumption—that the recrystallization happened at the time of the impact, or that the mass extinctions, if caused by the asteroid, would have happened around the time of the impact, for example.

Answer Explanation:
This answer is a necessary premise for the old theory, but the new theory is that the meteorite that made that crater can't be responsible for the mass extinction. As such, it doesn't need to be the case that it was large enough to cause the extinctions, even if it's rebutting an argument that requires that assumption. If anything, the negation of this answer supports the conclusion.

Key Takeaway:
Causality is inherently linked to a timeline, so always think about that element when dealing with an argument that brings up causality (whether to conclude there was or wasn't causality). Also, whenever the argument uses one thing as a proxy for another (here, the polarity of the rock at the impact site as a proxy for when the meteorite struck), there's always a chance that it's a bad proxy.

Incorrect. If the rock didn't recrystallize immediately, the impact may have happened at the time of the extinction/reversed polarity and then the polarity shifted before the rock recrystallized. That would undermine the rebuttal, so this answer is necessary for the argument.

Incorrect. If the rocks at the impact site were melted after the meteorite during a time of normal polarity, then they would have re-recrystallized and locked in that normal polarity, allowing for the original impact to have happened during a time of reversed polarity. Since the argument assumes this didn't happen, this answer represents a necessary premise.

Incorrect. If the recrystallized rocks didn't melt because of the impact, then there's no tying the polarity that they took on when recrystallizing to the impact/extinctions. As such, it's not good evidence against the impact. So the argument assumes that the meteorite caused the melting, and the polarity locked in was during the same time.

Incorrect. This answer also addresses the timeline element of the stimulus. If the extinctions were caused by the meteorite but they took some time to happen, then the polarity at the time of the extinctions may not match that of the crater, despite the causal relationship.