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Difficulty: HardMethod of Reasoning

Geochemist: Some volcanologists argue that the sudden spike in atmospheric sulfur dioxide recorded in ancient subpolar ice cores was caused by the eruption of Mount Hekla around 1100 BCE, pointing out that tephra layers in adjacent peat deposits date to roughly that era. However, this conclusion is premature. Cryogenic analysis shows that the sulfur particles in the ice core exhibit a distinctive mass-independent fractionated isotopic signature that forms exclusively in the upper stratosphere. Mount Hekla's plume height during that period was insufficient to inject gases into the stratosphere, which indicates that the ice-core sulfur must have originated from an equatorial volcano with far greater explosive power.

Which of the following most accurately describes the method of reasoning employed by the geochemist?

  1. challenging a causal claim by presenting physical evidence that the phenomenon in question required conditions the purported cause could not have generatedAnswer
  2. B
    rejecting a causal hypothesis on the grounds that the evidence offered in its favor relies on inaccurate dating of adjacent deposits
  3. C
    treating a finding that provides indirect support for an alternative origin as conclusive proof that no regional volcanic activity occurred
  4. D
    inferring that because stratospheric injection requires powerful eruptions, any absence of high-altitude sulfur rules out past volcanic eruptions
  5. E
    attempting to refute an empirical hypothesis by arguing that a general geochemical law has exceptions in subpolar environments

Answer

Challenging a causal claim by presenting physical evidence that the phenomenon in question required conditions the purported cause could not have generated.
The geochemist refutes the volcanologists' causal hypothesis by showing that the sulfur spike possesses a specific physical property—mass-independent isotopic fractionation requiring stratospheric formation—that could not have been produced by Mount Hekla, whose plume was insufficient to reach the stratosphere.

Step-by-Step Solution

1
Identify the opposing position and its supporting evidence
The opposing view claims the 1100 BCE sulfur spike was caused by Mount Hekla, based on temporally correlating tephra layers in nearby peat.
Establishing the target claim is essential for evaluating how the author seeks to undermine it.
2
Analyze the author's counter-evidence and logical mechanism
The author introduces isotopic data showing the sulfur must have reached the stratosphere, and pairs this with evidence that Mount Hekla's plume could not reach stratospheric altitudes.
This establishes a mismatch between the necessary conditions for the observed effect and the capabilities of the proposed cause.
3
Abstract the overall argumentative technique
The author refutes a proposed causal explanation by showing that the phenomenon possesses an essential feature that the proposed cause could not produce.
Method of reasoning questions require matching the concrete argumentative steps to an accurate, abstract structural description.

Key Concept

Identifying Argumentative Technique (Causal Refutation via Physical Constraint Mismatch)
Estimated Time:1m 30s
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Topics

Method of Reasoning

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