PrepTest 117, Section 2, Question 15
According to current geological theory, the melting of(68 more words not shown)
Which one of the following,(7 more words not shown)
- AThe earth's crust(14 more words not shown)
- BThere are various(11 more words not shown)
- CEvidence of severe(19 more words not shown)
- DSevere earthquakes are(12 more words not shown)
- EAsteroid impacts, which(13 more words not shown)
Reading the argument
The ice melted, and Sweden had earthquakes. How are those events connected?
The geological theory gives us part of a story: melting removed weight pressing on the earth's crust, and pressure from below then produced lasting cracks in some places. That helps explain the cracks. It doesn't yet explain the earthquakes in Sweden.
Were those cracks in Sweden? The passage hasn't specified that. And do cracks of this kind cause earthquakes? We shouldn't treat any disturbance of the surface as enough—digging a trench in a neighborhood doesn't by itself establish a cause of an earthquake. We need a connection between the geological cracking described here and the earthquakes, rather than simply noticing that events occurred around the same time.
What we’re looking for
We're asked to strengthen the argument, so we don't need to settle every question we've raised. Evidence putting the relevant cracks in Sweden would help. Evidence linking this cracking to earthquakes would also help. Either could make the proposed explanation more plausible even if another gap remained.
Working the answers
- A
This connects changes in pressure with cracking, a connection the passage has already supplied for the melting ice. It doesn't take us from those cracks to earthquakes in Sweden. The missing link we're trying to support is farther along the explanation.
- B
Northern Europe is broader than Sweden. Cracks in various parts of that region don't establish that the relevant cracks were near Sweden's earthquakes. B also doesn't connect the cracks to the end of the Ice Age or establish their relationship to earthquakes. It supplies nearby-sounding geography without the connection we need.
- C
Earthquakes in northern Canada are more events to explain. C doesn't say what caused those earthquakes or how they establish the cause of Sweden's earthquakes. A second place experiencing earthquakes around the same time doesn't fill in the proposed mechanism.
- DCorrect
This connects severe earthquakes with cracking near the earthquake site. Cracking is now identified as the usual source of severe earthquakes near a site, so the cracks produced by pressure changes have a plausible role in the explanation.
We still haven't directly established that the ice-related cracks occurred at the Swedish sites. D therefore doesn't prove the author's conclusion. It does address one important gap by linking cracking to earthquakes, which makes the proposed contribution from melting ice more plausible.
- E
This offers another possible explanation for the earthquakes: asteroid impacts around the same time. It doesn't connect melting ice with Sweden's earthquakes. To the extent it supplies a competing cause, it gives us a reason to question the explanation rather than additional support for it. It also needn't prove that melting ice played no role to fail as a strengthener.
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