LSAT 117 | Section 2 | Logical Reasoning: Q15

LR Question 15 Explanation

QUESTION TEXT: According to current geological theory …

QUESTION TYPE: Strengthen

CONCLUSION: It’s likely that the melting of the ice contributed to the earthquakes.

REASONING:

• Melting ice reduced the weight on parts of the earth’s crust.
• Reduced pressure caused lasting cracks in some areas of the crust.
• Sweden experienced severe earthquakes at the end of the Ice Age.

ANALYSIS: The premises give us: Melting ice → cracks in the earth’s crust

But the conclusion is about earthquakes. We need evidence connecting cracks to earthquakes to strengthen the conclusion.

Imagine:

• A storm caused many trees to fall.
• The power went out.
• So the storm probably contributed to the power blackout.

The missing link is that fallen trees often knock down power lines. You might think that’s too obvious to state or that the link between storms and blackouts is so natural that it doesn’t need explaining, but on the LSAT it does.

Similarly, even though you can reasonably understand that cracks would cause earthquakes, that’s still something that needs to be stated to support the conclusion.

___________

1. Tempting because it says sudden pressure changes tend to cause cracks. But we already know this from the premises. It doesn’t connect cracks to earthquakes.
2. The existence of cracks elsewhere in Northern Europe doesn’t show that the cracks caused Sweden’s earthquakes.
3. Earthquakes in northern Canada do not establish why Sweden’s earthquakes occurred.
4. CORRECT. If severe earthquakes are generally caused by cracking of the earth’s crust near the earthquake site, then: Melting ice → crustal cracking → earthquakes. Now we have a clean chain that supports the conclusion.
5. This gives an alternative cause (asteroid impacts). That would weaken the argument because it gives us less reason to believe that melting ice caused the earthquakes.