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Difficulty: MediumIdentifying Underlying Assumptions and Premises

Trace amounts of methane (CH4CH_4) have been detected in the atmosphere of Mars. Since solar ultraviolet (UV) radiation rapidly destroys atmospheric methane, its ongoing presence implies a continuous source of replenishment. Two scientists propose different mechanisms for how this methane is generated and released.

Scientist 1
The methane is biogenic, produced by methanogenic microorganisms living in liquid water aquifers deep beneath the Martian surface. These microbes survive in the warm subsurface heated by geothermal activity. During warmer Martian seasons, ground ice thaws, forming fractures through which the accumulated methane escapes into the atmosphere.

Scientist 2
The methane is abiogenic, produced by serpentinization. In this process, liquid water reacts with olivine-rich rocks deep inside the crust to produce hydrogen gas (H2H_2). This hydrogen then reacts with carbon dioxide (CO2CO_2) under high temperatures and pressures to form methane. The methane is stored in subsurface ice structures called clathrates, which seasonally destabilize and release the gas.

Which of the following is an underlying assumption shared by both Scientist 1 and Scientist 2?

  1. Liquid water is present in the Martian subsurface.Answer
  2. B
    Active microbial life exists within Martian subsurface aquifers.
  3. C
    Olivine-rich volcanic rocks are abundant in the Martian crust.
  4. D
    Martian methane is temporarily stored in clathrate cages before being released.

Answer

Liquid water is present in the Martian subsurface.
The correct option identifying the presence of liquid water is correct because both models require liquid water to function. Scientist 1's hypothesis depends on microbial life surviving in liquid water aquifers, and Scientist 2's hypothesis depends on liquid water reacting with volcanic rocks. Neither scientist provides direct proof that liquid water currently exists under the Martian surface; therefore, its existence is an unstated, shared assumption necessary for both theories to remain plausible.

Step-by-Step Solution

1
Analyze Scientist 1's proposed mechanism for methane production.
Scientist 1 suggests methanogenic microbes produce methane in deep subsurface liquid aquifers.
To identify the environmental conditions required for Scientist 1's model to function.
2
Analyze Scientist 2's proposed mechanism for methane production.
Scientist 2 suggests serpentinization occurs when liquid water reacts with olivine-rich rocks.
To identify the environmental conditions required for Scientist 2's model to function.
3
Compare the prerequisites of both models to find the common factor.
Both models rely on the presence of liquid water beneath the Martian surface (one as a biological medium, the other as a chemical reactant) without presenting direct evidence of its existence.
To determine the shared underlying assumption necessary for both hypotheses to be valid.

Key Concept

Identifying underlying assumptions in conflicting scientific viewpoints
Estimated Time:1m 30s
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Topics

Identifying Underlying Assumptions and Premises

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