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Question

Difficulty: HardRole in Argument

Consider the following argument:

Astrobiologist: Planetary scientists often assume that detecting atmospheric methane on an Earth-sized exoplanet provides definitive evidence of biological activity. However, serpentinization reactions involving ultramafic mantle rock can generate abiotic methane plumes of comparable magnitude. Furthermore, planetary composition models confirm that the target exoplanet is exceptionally rich in olivine-bearing rock, ensuring high rates of abiotic methane generation under hydrothermal conditions. Therefore, the detection of methane in this exoplanet's atmosphere would fail to establish the presence of biological organisms.

Match each excerpted statement from the passage with the precise argumentative function it performs.

  • Detecting atmospheric methane on an Earth-sized exoplanet provides definitive evidence of biological activity.A widely held background assumption that the overall argument is designed to challenge.
  • Serpentinization reactions involving ultramafic mantle rock can generate abiotic methane plumes of comparable magnitude.A general empirical principle introduced to demonstrate that a specific observed phenomenon has non-biological causal mechanisms.
  • The target exoplanet is exceptionally rich in olivine-bearing rock, ensuring high rates of abiotic methane generation under hydrothermal conditions.A supporting factual premise that applies the general geological mechanism directly to the specific celestial body under investigation.
  • The detection of methane in this exoplanet's atmosphere would fail to establish the presence of biological organisms.The overarching conclusion that the argument as a whole aims to establish.

Answer

The statement identifying methane as definitive proof of life matches the background assumption challenged by the argument; the statement about serpentinization generating abiotic methane matches the general empirical principle showing alternative causal mechanisms; the statement about the target exoplanet's olivine-rich mantle matches the supporting factual premise applying the principle to the case at hand; and the statement that methane detection would not establish life on the target planet matches the overarching conclusion of the argument.
The argument proceeds by identifying a prevailing assumption, offering an empirical principle that provides an alternative explanation, supplying specific factual evidence that the alternative mechanism is operative in the case under consideration, and inferring that the prevailing assumption does not hold for that case.

Step-by-Step Solution

1
Isolate the overall conclusion and opposing viewpoint in the stimulus.
Identified the final sentence as the main conclusion and the opening sentence as the target opposing assumption.
The author explicitly rejects the common assumption by showing why methane on this specific planet does not prove life.
2
Distinguish between the general scientific rule and its specific factual application.
Categorized the serpentinization statement as a universal geochemical principle and the olivine-bearing composition statement as a case-specific factual premise.
The argument requires both a general causal mechanism (serpentinization) and evidence that the required conditions exist on the target planet (olivine richness) to support its conclusion.
3
Correlate each statement directly with its functional description.
Formed unambiguous structural pairings based on functional dependencies.
Each statement serves a distinct, non-overlapping role within the multi-tiered argumentative structure.

Key Concept

Argumentative Role Identification in Multi-Layered Reasoning
Estimated Time:2m 0s
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Topics

Role in Argument

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