LSAT 105 | Section 4 | Logical Reasoning: Q5

LR Question 5 Explanation

QUESTION TEXT: The most reliable way to detect the presence of life …

QUESTION TYPE: Weaken

CONCLUSION: The most reliable way to detect life on a planet is to check whether there’s methane in its atmosphere.

REASONING: Methane only remains in an atmosphere if it’s constantly replenished by living beings.

ANALYSIS: We only know methane needs living beings to stay.

So if methane ➞ life

That does not mean life needs methane. We do not know: If life ➞ methane

But the conclusion is that methane is the most reliable indicator of life.

The best way to weaken that is to show that you can have life without methane. If many living things don’t produce methane, then a planet could have life but no methane. In that case, looking for methane would miss some inhabited planets, making it a less reliable test for life.

___________

1. It only argued that methane is the most reliable method. The existence of other methods alone doesn’t tell us whether they’re equally reliable or more reliable.
2. CORRECT. So a planet could contain living organisms and still have no methane in its atmosphere. If the test misses some planets with life, it’s not a very reliable way to detect life.
3. The argument is about what would be the most reliable indicator in principle, not what we currently have the technology to detect.
4. Small amounts of methane may still accumulate or be detectable. This answer doesn’t establish that methane would fail as an indicator of life.
5. We know very little about other planets. The fact that we currently know of only one methane-containing atmosphere doesn’t undermine the claim that methane would be a reliable indicator of life.