LSAT 155 | Section 1 | Logical Reasoning: Q23

LR Question 23 Explanation

QUESTION TEXT: On Earth, biological activity leads to a change in the ratio…

QUESTION TYPE: Weaken

CONCLUSION: It is unlikely that life occurred on Mars.

REASONING: Biological activity changes the ratio of isotope S-34 to S-32. A meteorite from Mars has ratios of these elements that matches the ratio found on Earth before life began.

ANALYSIS: The author is drawing a connection between pre-life Earth and Mars. Because the ratio matches pre-life Earth, it must mean that Mars also has no life.

This is not an especially strong argument, as it’s based only on this one shared characteristic between Mars and pre-life Earth. The answers that weaken this argument will give us a reason to doubt the value of this shared characteristic. Because it’s a Weaken Except question, we need to look at the answers and figure out which one doesn’t weaken the argument.

___________

1. This answer does weaken the argument. It tells us that not all life has the same effect on the ratio, so we can’t infer that there is no life based on just the ratio.
2. This weakens the argument by attacking the use of the ratio as evidence. The argument relies on the ratio comparison, so evidence attacking the comparability of the two planets will weaken it.
3. CORRECT. This answer doesn’t weaken the argument at all. In fact, it shows that the meteorite is representative of Mars as a whole. This actually protects the argument from one possible angle of attack.
4. This does weaken the argument. This tells us that it would be rare for a meteorite to show the changes in the ratio caused by life. If few mineral samples contain the changed ratio, it’s possible for a meteorite to not show that life exists.
5. This weakens the argument by showing that the meteorite isn’t even an accurate representation of Mars anymore. If the ratio on Mars has changed, then maybe there’s been life since the meteorite left.

Recap: The question begins with “On Earth, biological activity leads to a change in the ratio”. It is a Weaken question. Learn how to master LSAT Weaken questions on the LSAT Logical Reasoning question types page.