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Difficulty: MediumStrengthen

Paleoclimatologist: Sediment core samples extracted from Lake Sylvan reveal a dramatic spike in charcoal microparticles around 850 CE, closely accompanied by a sharp decline in pollen from old-growth oak forests and an influx of pioneer scrub vegetation. Although many historians attribute this abrupt ecological transformation to widespread land-clearing by early agrarian migrants, it is more likely that a severe, multi-decade regional drought sparked extensive natural wildfires that reshaped the landscape.

Which of the following, if true, most strongly supports the paleoclimatologist's hypothesis?

  1. A
    Old-growth oak trees are substantially more resilient to insect infestations and fungal pathogens than are most species of pioneer scrub vegetation.
  2. Sediment cores extracted from several remote, uninhabitable alpine tarns across the same climatic region exhibit the identical pattern of charcoal deposition and forest retreat dating to 850 CE.Answer
  3. C
    Archaeological excavations along the shoreline of Lake Sylvan have unearthed agricultural implements and domesticated grain residues reliably dated to the mid-ninth century.
  4. D
    Natural wildfires triggered by lightning strikes invariably generate far greater volumes of airborne particulate matter than do deliberate agricultural brush fires.
  5. E
    The pollen grains of pioneer scrub vegetation are transported over much greater distances by prevailing wind currents than are the heavier pollen grains of oak trees.

Answer

The statement showing that identical sediment patterns occurred simultaneously in uninhabited alpine tarns within the same climatic region provides the strongest support.
The paleoclimatologist argues that the 850 CE charcoal spike and vegetation shift were caused by a widespread climate phenomenon (severe regional drought causing wildfires) rather than localized human clearing. The statement showing that remote, uninhabited alpine lakes in the same climate region underwent the exact same charcoal and forest transition at 850 CE strongly strengthens this conclusion. Because humans were absent from those alpine locations, human agriculture could not have caused the changes there, demonstrating that a regional, non-anthropogenic factor such as drought was the true common cause.

Step-by-Step Solution

1
Analyze the argument's premises, conclusion, and underlying gap
Premise: Sediment cores show a charcoal spike and forest-to-scrub transition at 850 CE. Rival claim: Human agricultural land-clearing caused it. Paleoclimatologist's conclusion: A multi-decade regional drought caused natural wildfires that drove the change.
Strengthening an argument that rejects an alternative causal explanation requires finding evidence that either rules out the rival cause or validates the proposed environmental mechanism.
2
Evaluate the impact of demonstrating the phenomenon in human-free environments
If remote, uninhabited lakes in the same climatic zone display identical charcoal spikes and forest retreat at the exact same time, the transition cannot be attributed to human agricultural activity.
Ruling out the rival explanation (human land-clearing) across a broader regional scope substantially increases the likelihood that a shared regional climate event (drought) was the primary driver.
3
Eliminate distractors that weaken, use unwarranted extremes, or address irrelevant biological traits
The correct choice is uniquely supportive, whereas other options introduce opposing evidence, overly broad absolutes, or irrelevant mechanisms.
Ensures that only the uniquely credited answer choice is selected under timed assessment criteria.

Key Concept

Strengthening Causal Arguments by Ruling Out Alternative Causes
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