QUESTION TEXT: In early 2003, scientists detected methane in…
QUESTION TYPE: Necessary Assumption
CONCLUSION: Any methane in Mars’ atmosphere must have been released recently.
REASONING: Scientists found methane on Mars in 2003. Methane falls apart when it’s hit by UV radiation from the sun.
ANALYSIS: This sounds like a good argument. So before you look at the answers, you should ask “how can this be wrong?”.
We know sunlight rapidly destroys methane. So for methane to survive, it must somehow avoid sunlight. The argument is assuming that sunlight reaches all methane and fairly quickly. If that’s not true, then some methane might persist in Mars’ atmosphere for a long time.
- It doesn’t matter what happened in the past. The argument is talking about whether methane is in the upper atmosphere now.
- CORRECT. If this isn’t true, then some methane might still be in the atmosphere.
Negation: Some methane in the upper atmosphere of Mars is never exposed to sunlight.
- This just mixes together three terms from the argument in an irrelevant way: “methane”, “detected”, “falls apart”. The argument never made any link between detection and falling apart. This is an answer designed to seem plausible only because the terms are familiar.
- The argument is saying that the methane that was detected had not yet been exposed. If it had been exposed to UV radiation, the methane would have fallen apart.
The point of the argument is that the methane that was detected will fall apart, in the future. The author is claiming that methane can exist on Mars, but only for a short time, before it is exposed to UV radiation and dissolves.
- It doesn’t matter what happens on Earth. The argument is about Mars. Maybe Earth’s methane is protected from UV radiation by some other factor….but this wouldn’t matter even if it were true.
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