LSAT 118 – Section 1 – Question 21

LSAT 118 - Section 1 - Question 21

December 2004

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT118 S1 Q21
+LR
Sufficient assumption +SA
Causal Reasoning +CausR
Link Assumption +LinkA
A
57%
167
B
26%
162
C
6%
164
D
9%
159
E
2%
158
149
161
174
 +Hardest 148.411 +SubsectionMedium

J.Y.’s explanation

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Although the geological record contains some hints of major meteor impacts preceding mass extinctions, there were many extinctions that did not follow any known major meteor impacts. Likewise, there are many records of major meteor impacts that do not seem to have been followed by mass extinctions. Thus the geological record suggests that there is no consistent causal link between major meteor impacts and mass extinctions.

Summary
The author concludes that there is no consistent causal link between major meteor impacts and mass extinctions. This is the based on the following:
Many extinctions didn’t follow major meteor impacts.
Many major meteor impacts were not followed by mass extinctions.

Missing Connection
The premises don’t establish what implies that there’s “no consistent causal link” between major meteor impacts and mass extinctions. Although we know that many extinctions didn’t follow such impacts, and that many impacts weren’t followed by such extinctions, how do we know that this isn’t a consistent causal link?
We want to establish that if many extinctions didn’t follow major meteor impacts or if many major meteor impacts were not followed by mass extinctions, then this proves there’s no consistent causal link between such impacts and such extinctions.

A
If there were a consistent causal link between major meteor impacts and mass extinctions, then all major meteor impacts would be followed by mass extinctions.
(A) establishes that in order for there to be a consistent causal link between the impacts and mass extinctions, then ALL major meteor impacts would be followed by such extinctions. We know from one of our premises that many major meteor impacts were NOT followed by such extinctions. This triggers the contrapositive of (A), which would establish that there is NO consistent causal link.
B
Major meteor impacts and mass extinctions cannot be consistently causally linked unless many mass extinctions have followed major meteor impacts.
(B) establishes that in order for there to be a consistent causal link, it’s required that many mass extinctions have followed major meteor impacts. But we don’t know that this requirement hasn’t been met. Although we do know that many mass extinctions have followed major meteor impacts, it’s still possible that many such extinctions have followed such impacts.
C
Of the mass extinctions that did not follow any known major meteor impacts, few if any followed major meteor impacts of which the geological record contains no hints.
(C) doesn’t establish what is required for a “consistent causal link” between extinctions and meteor impacts, so it can’t make the argument valid.
D
If there is no consistent causal link between major meteor impacts and mass extinctions, then not all mass extinctions could have followed major meteor impacts.
(D) establishes what would be true IF there is no consistent causal link. But we’re trying to reach the conclusion that there is no consistent causal link. We don’t want “no consistent causal link” to appear in the “IF” part of an “If, then” answer. We want it to appear in the “then” part.
E
There could be a consistent causal link between major meteor impacts and mass extinctions even if not every major meteor impact has been followed by a mass extinction.
(E) tells us about one circumstance under which there can be a consistent causal link. But we’re trying to prove that there’s NO consistent causal link.

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LSAT PrepTest 118 Explanations

Section 1 - Logical Reasoning

Section 2 - Reading Comprehension

Section 3 - Logical Reasoning

Section 4 - Logical Reasoning

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