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Difficulty: HardAligning Data and Predictions with Viewpoints

A rover on Mars detected simple chlorinated organic molecules in several rock samples. Two hypotheses were proposed to explain the origin and distribution of these molecules.

Hypothesis 1
Organic molecules on Mars are biotic in origin, representing the remains of ancient microbial life. These microorganisms thrived in wet, lacustrine (lake) environments. As they died, their organic debris was adsorbed by clay minerals in mudstone formations, which protected the organics from degradation. In contrast, basaltic (igneous) rocks formed from volcanic flows that were too hot to support life and lacked the clay minerals necessary for preservation. Therefore, clay-rich mudstones will contain high concentrations of organic molecules, whereas basaltic rocks will contain negligible concentrations, regardless of how long the rocks have been exposed to cosmic radiation at the Martian surface.

Hypothesis 2
Organic molecules on Mars are abiotic in origin, having been delivered to the surface by carbonaceous chondrite meteorites. These meteorites deposit organic matter uniformly across all rock types. However, once deposited, these molecules are slowly altered by cosmic radiation and ultraviolet light into the specific chlorinated organic compounds detected by the rover. Consequently, the concentration of these chlorinated organic compounds is directly proportional to a rock's surface exposure age (the total time a rock has been exposed directly to cosmic radiation). Basaltic rocks and clay-rich mudstones with similar surface exposure ages will contain similar concentrations of these organic molecules.

Suppose scientists analyze a sample of clay-rich mudstone (Sample A) with a surface exposure age of 10 million years10\text{ million years}, and a sample of basalt (Sample B) with a surface exposure age of 150 million years150\text{ million years}. Based on the two hypotheses, which of the following predictions regarding the concentrations of chlorinated organic molecules in these samples is correct?

  1. A
    According to Hypothesis 1, Sample B will have a higher concentration of organic molecules than Sample A because Sample B has a greater surface exposure age.
  2. B
    According to Hypothesis 1, Sample A and Sample B will have similar concentrations of organic molecules because they are from the same geological era.
  3. C
    According to Hypothesis 2, Sample A will have a higher concentration of organic molecules than Sample B because clay-rich mudstone is more shielding.
  4. According to Hypothesis 2, Sample B will have a higher concentration of organic molecules than Sample A because Sample B has been exposed to cosmic radiation for a longer duration.Answer

Answer

According to Hypothesis 2, Sample B will have a higher concentration of organic molecules than Sample A because Sample B has been exposed to cosmic radiation for a longer duration.
According to Hypothesis 2, the concentration of chlorinated organic compounds is directly proportional to a rock's surface exposure age, independent of the rock type. Since Sample B has a much higher surface exposure age (150 million years150\text{ million years}) than Sample A (10 million years10\text{ million years}), Hypothesis 2 predicts that Sample B will have a higher concentration of these molecules.

Step-by-Step Solution

1
Identify the key parameters of the two samples from the prompt.
Sample A is a clay-rich mudstone with a surface exposure age of 10 million years10\text{ million years}. Sample B is basalt with a surface exposure age of 150 million years150\text{ million years}.
This establishes the rock type and surface exposure age variables needed to evaluate each hypothesis.
2
Apply the logic of Hypothesis 1 to the samples.
Hypothesis 1 states clay-rich mudstone has high organic concentration, while basalt has negligible concentration, independent of surface exposure age. Therefore, Hypothesis 1 predicts Sample A will have a higher concentration than Sample B.
This determines the predicted relationship between the samples under the first viewpoint.
3
Apply the logic of Hypothesis 2 to the samples.
Hypothesis 2 states organic concentration is directly proportional to surface exposure age, regardless of rock type. Since Sample B's exposure age (150 million years150\text{ million years}) is greater than Sample A's (10 million years10\text{ million years}), Hypothesis 2 predicts Sample B will have a higher concentration than Sample A.
This determines the predicted relationship between the samples under the second viewpoint.
4
Compare these predictions to the choices to find the matching statement.
The option stating that under Hypothesis 2, Sample B will have a higher concentration due to its longer exposure duration matches our deduction in Step 3.
This identifies the correct option based on the logical mapping of the data to the viewpoints.

Key Concept

Aligning Data and Predictions with Viewpoints
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Topics

Aligning Data and Predictions with Viewpoints

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