Logical reasoning PrepTest 117 · Section 4 · Question 17

Question prompt

Climatologists believe they know Remaining source text redacted.
Why the credited answer is right

Credited answer: D

The notes below walk through why it fits the stem and how to eliminate the rest.

Argument or Facts

Argument

Valid or Flawed

Flawed

Question Type

Bizarro / Strengthen Questions

Stimulus Summary

Hypothesis - The Earth passes through cosmic dust, dimming the sun, causing ice ages
Support - Starting about 800,000 years ago, there have been regular ice ages that coincide with Sun fluctuations
Concession/Possible issue - The dust clouds would have to be pretty dense to cause this

Answer Anticipation

There’s a lot going on in this argument, so let’s tackle it using our normal process and then take a look at some of the oddities.
First, the question stem asks us to find answers that strengthen a hypothesis (and rule those out). At this point, you should be trying to identify the hypothesis, and expecting it to be causal, as most hypotheses are. And it is! Cosmic dust causes the sun’s rays to be dimmed, thus resulting in an ice age.
Is this based on a correlation? It is - the ice ages starting about 800,000 years ago coincide with Sun fluctuations. Since we have a correlation/causation flaw, we can strengthen this argument with the usual answers:
Eliminate an alternative cause Find more examples of cause and effect going together Show that the cause being absent results in the effect being absent
On top of these, however, two features of the argument suggest other potential answers.
First, the causality in the conclusion doesn’t directly relate the correlated elements. The Sun fluctuations and ice ages are linked in the correlation, but the causation is about dust clouds. So any answer that links the dust clouds to the Sun fluctuations in an exclusive manner (or even a probable one) will strengthen this argument.
Second, the stimulus brings up a concession - something that the climatologists believe to be true that creates a potential issue for their argument. That concession is that, to have the hypothesized effect, the cosmic dust clouds would need to be “particularly dense,” so any answer establishing that they are will address that concession and strengthen the argument.
There are a lot of anticipated answers here, which is good because we need to find 4 that fall into these categories in order to eliminate them and find the correct answer!

Answer choices

  1. A
    Earth did not pass Remaining source text redacted.
    Why choice A is not credited
    This answer can seem out of scope, but it actually strengthens the argument by showing that the cause being absent is correlated with the effect being absent. The ice ages began about 800,000 years ago. If the cosmic dust clouds are the cause of those ice ages, it’d be expected that they wouldn’t exist before the ice ages started. In establishing that to be true, this answer strengthens the argument.
  2. B
    Two large asteroids collided Remaining source text redacted.
    Why choice B is not credited
    This answer connects cosmic dust clouds to the timeline, showing that the hypothesized cause showed up just as the hypothesized effect did. That strengthens the argument for a causal relationship between the two.
  3. C
    Earth's average temperature drops Remaining source text redacted.
    Why choice C is not credited
    This answer addresses the first of the two additional features of the argument we mentioned, as well as addressing the correlation/causation. There’s no premise in the argument that supports dust clouds can cause the Sun fluctuations/dimming of the Sun that leads to ice ages. This answer associates dust clouds with a drop in the average temperature, which connects dust to the Earth being cold and thus gets us a step closer to those ice ages.
  4. D
    Large bits of cosmic Remaining source text redacted.
    Why choice D matches the stem
    This answer is very close to serving as a strengthener...but it falls short by failing to link this cosmic rock and dust to any changes in temperature. If the periodic nature of this coincided with ice ages, then this analysis would be very different, but in failing to tie anything to the hypothesized effect, this answer doesn’t affect the argument and is thus the correct answer.
  5. E
    Rare trace elements known Remaining source text redacted.
    Why choice E is not credited
    This answer creates a correlation between the Earth passing through cosmic dust (which would count as debris) and the ice ages, thus strengthening the argument for a causal relationship between them.

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A 17%
  2. B 7%
  3. C 23%
  4. D Credited 47%
  5. E 6%

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