PrepTest 127, Section 1, Question 7
Two different dates have been offered as the(69 more words not shown)
The statements above, if true,(20 more words not shown)
- AToward the end(20 more words not shown)
- BAmong those sediments(24 more words not shown)
- CIce masses continued(16 more words not shown)
- DThe species of(20 more words not shown)
- EToward the end(25 more words not shown)
Reading the argument
We have two proposed dates for the end of the ice age, based on two different changes. The insect evidence tells us when warm-adapted beetles replaced cold-adapted beetles. The pollen evidence tells us when spruce forests became established where there had been ice.
Those changes need not happen at exactly the same time. Even after conditions become suitable, trees take time to become a forest. A biological sign of a changing climate could therefore lag behind the change itself. We should not assume that either measurement marks the precise instant the ice age ended.
What is clear is their order. The warm-adapted beetles arrived more than 500 years before the spruce-forest date. Keep that simple relationship in view while reading the complicated choices: beetles first, forests later.
What we’re looking for
The question asks what the evidence most strongly supports. I expect something about the beetles becoming established sooner than the forests. We do not need to decide a definitive end date for the ice age or invent a history of what happened to every beetle species.
Working the answers
- A
This says the warm-adapted beetles stopped inhabiting spruce-covered areas. We know the beetles appeared before the forests, not that they left when the forests arrived. Their later geographic overlap is a new issue.
- B
The evidence does not support expecting cold-adapted beetle fragments and spruce pollen together in these sediments. The warm-adapted beetles replaced the cold-adapted ones more than 500 years before the forest date. That sequence gives us no basis for the proposed association between the earlier cold-adapted beetles and the later forests.
- C
Ice masses advancing is different from ice taking time to give way to forest. Neither dating method establishes that ice continued spreading through North America after the ice age ended. We also have competing estimates of that ending, not an agreed date from which C's several hundred years can be measured.
- D
Being replaced in the sampled area does not establish that a species became extinct. The cold-adapted beetles could have moved to another suitable area. We are not told that they all died out, so D reaches beyond the evidence.
- ECorrect
The beetles became established on newly available ground faster than the spruce forests did. That fits the order supplied by the two dates: the insect change came first, with the forest change more than 500 years later. The references to soil changes and seed dispersion describe forest establishment; the key comparison is that this process took longer than the beetles' colonization. E captures the supported timing difference.
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