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Difficulty: MediumMethod of Reasoning

Geochemist: Some planetary scientists hypothesize that atmospheric methane detected on Mars originates from subsurface biological activity. However, if microbial organisms were generating this methane, the ambient atmospheric ratio of carbon-12 to carbon-13 isotopes would necessarily be elevated relative to abiotic baseline levels. High-precision isotopic spectroscopy has confirmed that the carbon isotope ratio in the Martian atmosphere matches standard abiotic baselines. Furthermore, non-biological serpentinization reactions beneath the crust produce methane at the exact concentrations observed. Therefore, the hypothesis that Martian methane is biological in origin is unsupported.

Arrange the following steps in the order that accurately reflects the logical progression of the geochemist's refutation from the initial conditional test to the final conclusion.

  1. 1Specifying a necessary observable condition that must hold if the biological hypothesis were correct.
  2. 2Presenting empirical evidence showing that this necessary observable condition does not obtain.
  3. 3Introducing an alternative abiotic mechanism that accounts for the observed phenomenon.
  4. 4Drawing the ultimate conclusion that the proposed biological explanation is unsupported.

Answer

The correct logical progression begins by specifying the necessary condition implied by the hypothesis, followed by presenting empirical evidence that denies this condition, introducing an alternative abiotic explanation for the observation, and finally drawing the main conclusion that the biological hypothesis is unsupported.
The argument follows a classic refutational structure: first establishing a necessary consequence of the opposing hypothesis (elevated carbon isotope ratios), next demonstrating that empirical observations contradict this consequence, then introducing a competing abiotic mechanism that accounts for the observed data, and finally asserting that the original hypothesis is unsupported.

Step-by-Step Solution

1
Identify the conditional premise set up to evaluate the hypothesis
The author establishes that biological generation requires an elevated carbon-12 to carbon-13 ratio.
This creates the logical benchmark necessary to test the opposing claim.
2
Identify the empirical finding that falsifies the conditional implication
Spectroscopy shows isotope ratios matching abiotic baselines rather than elevated levels.
Demonstrating the absence of a necessary consequence undermines the hypothesis via modus tollens.
3
Identify the supporting premise offering a competing causal explanation
Abiotic serpentinization accounts for the observed methane concentrations.
Providing a viable alternative explanation eliminates the need to invoke biological activity.
4
Identify the main conclusion derived from the combined premises
The hypothesis attributing Martian methane to biological activity is unsupported.
The conclusion logically synthesizes the falsified prediction and the alternative explanation.

Key Concept

Method of Reasoning: Indirect Refutation and Alternative Causal Account
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Method of Reasoning

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