### Methane on Mars Two scientists debate the origin of methane (\text{CH}_4) detected in … — ACT

### Methane on Mars

Two scientists debate the origin of methane ( $\text{CH}_4$ ) detected in the atmosphere of Mars.

Scientist 1
Mars's atmospheric methane is produced by subsurface methanogenic microbes. Because ultraviolet (UV) radiation rapidly destroys atmospheric methane, an active biological source must exist. Microbial metabolic activity fluctuates with temperature. Consequently, atmospheric methane concentrations will vary seasonally, peaking in the warmer summer months and dropping significantly during winter. Furthermore, this biological process does not generate substantial amounts of molecular hydrogen ( $\text{H}_2$ ).

Scientist 2
Martian methane is produced geologically through serpentinization, an abiotic reaction between liquid water, carbon dioxide, and olivine minerals in the subsurface. This geological reaction is continuous and unaffected by surface temperature changes. Therefore, methane release rates remain constant year-round. Additionally, serpentinization produces molecular hydrogen ( $\text{H}_2$ ) as a primary byproduct alongside methane in equal proportions. Thus, areas with atmospheric methane should also exhibit elevated $\text{H}_2$ levels.

A space probe monitored the atmospheric composition at a crater on Mars over one Martian year. The seasonal average concentrations of methane and hydrogen are shown in the table below:

Season	Methane concentration (ppb)	Hydrogen ( $\text{H}_2$ ) concentration (ppb)
Spring	$1.5$	$0.1$
Summer	$5.8$	$0.1$
Autumn	$1.6$	$0.1$
Winter	$0.2$	$0.1$

Based on the provided information, do the data in the table better support the viewpoint of Scientist 1 or Scientist 2?

Scientist 1, because the methane concentration varied seasonally and the hydrogen concentration remained low and constant.Answer
B
Scientist 1, because both the methane and hydrogen concentrations peaked during the summer.
C
Scientist 2, because the methane concentration peaked during the summer and the hydrogen concentration was constant.
D
Scientist 2, because the methane concentration was constant and equal to the hydrogen concentration in every season.

Answer

Scientist 1, because the methane concentration varied seasonally and the hydrogen concentration remained low and constant.

The correct answer accurately matches the observed data to Scientist 1's predictions. The table shows that the concentration of methane fluctuates significantly with the seasons, reaching a peak of

5.8\text{ ppb}

in the summer and dropping to

0.2\text{ ppb}

in the winter, which matches Scientist 1's prediction of seasonal variation. Additionally, the molecular hydrogen concentration remains low and constant at

0.1\text{ ppb}

in all seasons, which aligns with Scientist 1's assertion that biological methane production does not produce significant amounts of hydrogen.

Step-by-Step Solution

Analyze the predictions of both scientists.

Scientist 1 predicts that methane concentration varies seasonally (peaking in summer, dropping in winter) and hydrogen concentration remains low. Scientist 2 predicts that methane concentration remains constant year-round and hydrogen concentration matches methane concentration (elevated levels).

This establishes the criteria for evaluating the data against each hypothesis.

Examine the data table for seasonal trends in methane and hydrogen concentrations.

Methane varies seasonally (

1.5\text{ ppb}

in spring,

5.8\text{ ppb}

in summer,

1.6\text{ ppb}

in autumn,

0.2\text{ ppb}

in winter). Hydrogen remains constant at

0.1\text{ ppb}

across all seasons.

This extracts the empirical findings from the experiment.

Match the empirical findings to the predictions of the scientists.

The seasonal variation in methane and the consistently low hydrogen support Scientist 1's model, while contradicting Scientist 2's predictions of constant methane and elevated hydrogen.

This identifies the correct viewpoint supported by the data.

Key Concept

Aligning experimental data containing multiple variables with the conflicting predictions of two hypotheses.

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