LSAT 118 | Section 1 | Logical Reasoning: Q21

LR Question 21 Explanation

QUESTION TEXT: Although the geological record contains some hints …

QUESTION TYPE: Sufficient Assumption

CONCLUSION: There’s no consistent causal link between big meteor impacts and mass extinctions.

REASONING: The geological record shows:

• Many mass extinctions that did not follow any known major meteor impact.
• Many major meteor impacts that were not followed by mass extinctions.

ANALYSIS: The argument is trying to conclude: no consistent causal link.

It’s saying: If impacts and extinctions were consistently linked, we would expect major impacts to be followed by extinctions.

But the record shows many major meteor impacts that were not followed by mass extinctions.

So to make the conclusion follow, we need the rule:

A consistent causal link would require every major meteor impact to be followed by a mass extinction.

Once we have that, the argument works.

Consistent causal link → all major meteor impacts followed by mass extinctions.
But not all major meteor impacts were followed by mass extinctions.
Therefore, no consistent causal link.

___________

1. CORRECT. This supplies the missing rule that I explained above. It allows us to conclude that there’s no consistent causal link.
2. Tempting trap. But B only says a consistent causal link requires MANY extinctions to follow meteor impacts. But the stimulus can allow that and still have many meteor impacts that were not followed by extinctions. So B is too weak. We need a stronger rule that tells us that ALL impacts would be followed by extinctions.
3. This focuses on the extinctions that didn’t follow any known meteor impacts and says they probably didn’t follow unknown ones either. But showing that some extinctions occurred without impacts doesn’t rule out impacts as a consistent cause when they do occur.
4. This is backwards. It says: No causal link → not all extinctions followed impacts. But we need something that helps prove no causal link, not something that follows from it.
5. This weakens the argument. It says a consistent causal link could exist even if not every meteor impact caused a mass extinction. But the argument relies on the opposite idea.