Logical reasoning PrepTest 151 · Section 2 · Question 16

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
There was a spike in sulfur on Venus, which can be caused by volcanoes. But no active volcanoes are known to exist on Venus, and atmospheres regularly shift chemical composition, so we shouldn't conclude a Venusian volcano caused the sulfur spike.

Answer Anticipation:
This argument is a bit strange on the LSAT. Usually, a correlation is given, and the author concludes causation. Here, the author is stating that it would be wrong to conclude causation, making it a bit trickier.

Since this isn't a correlation vs. causation flaw, we must look elsewhere for our anticipation. The two premises the author uses to question the causality should be our focus. The latter premise—regular chemical shifts in the atmosphere—is unlikely to be helpful, since the argument talks about a spike in sulfur which seems as if it would be outside of normal variation. However, the first premise is more promising—it states there are no identified volcanoes on Venus. That leaves open the possibility that there are unknown volcanoes. If that's the case, then the author's argument is much weaker.

Answer Explanation:
Right off the bat, we get an answer stating that scientists wouldn't identify volcanoes directly even if they existed. If that's true, then the author can't rely on a lack of known volcanoes to question if one of them caused the spike in sulfur.

Key Takeaway:
In science-based questions, the author will frequently try to hide the uncertainty of a premise by stating that there are no "known" or "identified" examples of something. This leaves open the possibility that the thing exists even though it hasn't been observed by scientists.

Incorrect. Without knowing the cause of this spike, or whether there were any active volcanoes back then, it's impossible to determine the impact of this answer.

Incorrect. A spike suggests an increase over the baseline, so even if Venus has more sulfur, a spike could still be measured relative to that higher level.

Incorrect. If these traces are visible for years after an eruption, that might explain how sulfur could be measured despite no volcanoes being active at this time, but it doesn't explain a sudden spike in sulfur, so this answer doesn't affect the argument.

Incorrect. Unless you have government clearance, you don't know that aliens exist on Venus, and thus you can't assume that there are aliens burning fossil fuels on Venus (or organic matter that turned into fossil fuels). We've said too much . . .