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Difficulty: MediumAligning Data and Predictions with Viewpoints

The crustal dichotomy of Mars refers to the sharp contrast between the southern highlands (thick, cratered crust) and the northern lowlands (thin, smooth crust). Two scientists discuss competing models for this dichotomy's origin.

Scientist 1
The dichotomy was caused by a single, giant impact early in Mars's history. A large body struck the northern hemisphere, stripping away the crust and leaving a vast basin. This model predicts that the boundary zone between the lowlands and highlands is abrupt, featuring a steep slope. Additionally, the extreme pressure of the impact would have instantly formed shock-metamorphosed minerals, such as stishovite, which should remain present along the boundary.

Scientist 2
The dichotomy was caused by asymmetric mantle convection. A giant hot mantle plume rose beneath the southern hemisphere, causing prolonged volcanism and crustal thickening there. This model predicts a gradual transition zone between the hemispheres, marked by ancient volcanic flows and faults rather than impact debris. Because volcanic pressures are far too low, no shock-metamorphosed minerals would have formed.

Suppose a new geologic survey of the dichotomy boundary reveals that the boundary is extremely abrupt (a steep crustal slope occurring over less than 15 km15\text{ km}) and that stishovite is entirely absent from the region. How does this new finding align with the predictions of the two scientists?

  1. The abruptness of the boundary supports Scientist 1, while the absence of stishovite supports Scientist 2.Answer
  2. B
    The abruptness of the boundary supports Scientist 2, while the absence of stishovite supports Scientist 1.
  3. C
    Both findings support Scientist 1, because Scientist 1 predicted an abrupt boundary and the absence of shock-metamorphosed minerals.
  4. D
    Both findings support Scientist 2, because Scientist 2 predicted a gradual transition and the presence of shock-metamorphosed minerals.

Answer

The abruptness of the boundary supports Scientist 1, while the absence of stishovite supports Scientist 2.
The correct answer correctly maps each piece of new data to the corresponding scientist's prediction. The steep slope (abrupt boundary) matches Scientist 1's prediction of an abrupt boundary zone. The absence of stishovite matches Scientist 2's prediction that no shock-metamorphosed minerals would form.

Step-by-Step Solution

1
Identify Scientist 1's predictions regarding the dichotomy boundary.
Scientist 1 predicts an abrupt boundary (steep slope) and the presence of shock-metamorphosed minerals like stishovite.
To establish a baseline of evidence that would support Scientist 1.
2
Identify Scientist 2's predictions regarding the dichotomy boundary.
Scientist 2 predicts a gradual transition zone (gradual slope) and the complete absence of shock-metamorphosed minerals.
To establish a baseline of evidence that would support Scientist 2.
3
Map the new findings (abrupt boundary and absent stishovite) to each scientist's predictions.
The abrupt boundary supports Scientist 1 (who predicted an abrupt zone) and contradicts Scientist 2 (who predicted a gradual zone). The absence of stishovite supports Scientist 2 (who predicted no shock minerals) and contradicts Scientist 1 (who predicted shock minerals would remain).
To determine the correct alignment of the data with both viewpoints.

Key Concept

Aligning Data and Predictions with Viewpoints
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Topics

Aligning Data and Predictions with Viewpoints

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