Difficulty: Easy

Average Score: 100%

On Earth, dunes are typically rendered inactive when the climate becomes moist and sand-trapping vegetation grows. On Mars, however, there is no vegetation, though there are inactive dunes. Dunes might also become inactive if they become buried beneath dust. However, because of interparticle forces, a slow accumulation of dust would not stop the sand's movement; instead, a thick layer of dust would have to be deposited in a single event - which is exactly what occurs when there is a volcanic eruption on Mars.

The author of the passage refers to a thick layer of dust that is deposited in a single event most likely in order to

Rationale

suggest a possible explanation for the inactivity of dunes found on Mars.

The author discusses the thick layer of dust deposited during volcanic eruptions on Mars to provide a rationale for why dunes become inactive in that environment. This explanation highlights a significant factor that distinguishes Martian dune dynamics from those on Earth, where vegetation plays a role in dune stabilization.

A (compare climatic conditions on Earth with those on Mars) YOUR ANSWER

While the passage does mention climatic differences between Earth and Mars, the primary focus is not a direct comparison of their climates. Rather, the emphasis is on the mechanisms affecting dune activity, particularly the role of dust accumulation on Mars.

B (compare active and inactive dunes) YOUR ANSWER

The passage does touch on the concepts of active and inactive dunes; however, it does not provide a thorough comparison. Instead, it specifically uses the scenario of dust accumulation to explain the inactivity of Martian dunes, making this choice less relevant to the author's intent.

C (compare dust dunes with sand dunes) YOUR ANSWER

The author does not make a direct comparison between dust dunes and sand dunes. The focus is on the effects of dust accumulation on the inactivity of sand dunes on Mars, rather than comparing the two types of dunes themselves.

D (describe the effects of vegetation on dunes found on Earth) YOUR ANSWER

Although vegetation's role in stabilizing dunes on Earth is mentioned, the primary purpose of highlighting dust accumulation on Mars is to explain dune inactivity in the absence of such vegetation. Therefore, this choice does not capture the author's main point.

Conclusion

The passage ultimately aims to explain the inactivity of dunes on Mars through the phenomenon of dust accumulation resulting from volcanic activity. By emphasizing that a thick layer of dust must be deposited in a single event, the author provides insight into Martian dune dynamics, differentiating them from those on Earth where vegetation plays a critical role in stabilizing active dunes.

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