SAT OwlLake sediments preserve a record of the plants that grew nearby, since pollen settles to the lake bottom each year. In cores taken from Lake Marren, a layer dated to about 4,000 years ago shows a sharp drop in oak and elm pollen. The same layer contains abundant charcoal, and the layers just above it show the first appearance of cereal pollen, along with pollen from weeds that grow mainly on disturbed ground. Taken together, these findings suggest that ______
Which choice most logically completes the text?
a drier climate gradually made the area unsuitable for oak and elm, which were replaced by grasses.
people cleared nearby forest, at least partly by burning it, in order to grow crops.
a wildfire destroyed the forest, which then quickly grew back.
oak and elm pollen breaks down in sediment faster than cereal pollen does.
Show answer and explanation
Answer: B
Tree pollen drops sharply in the same layer as heavy charcoal, and just afterward cereal pollen and weeds of disturbed ground appear for the first time. Burning followed by crops and weeds points to people clearing forest for farming, choice B.
Choice A explains the loss of trees but not the charcoal or the sudden arrival of cereal crops, which point to human activity.
Why the other choices are wrong
- A. A drying climate wouldn't explain the charcoal or the first appearance of cereal pollen, and the drop was sharp, not gradual.
- C. The layers above show cereals and weeds, not returning oak and elm, so the forest did not quickly grow back.
- D. The tree pollen drops at one particular layer. A general difference in decay rates wouldn't produce a sudden change.
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