Which of the following provides the strongest evidence that Mars once had rivers and running water?

• A. The presence of dry riverbeds and valley networks visible on the Martian surface
• B. The discovery of large volcanoes such as Olympus Mons on Mars
• C. The detection of polar ice caps composed mainly of frozen carbon dioxide
• D. The thin carbon dioxide atmosphere currently surrounding Mars

Answer: (A)

Verified step by step guidance

1. Step 1: Begin by analyzing the question to understand what it is asking. The question is about identifying evidence that Mars once had rivers and running water. This means we need to focus on geological features or phenomena that suggest the presence of liquid water in the past.
2. Step 2: Evaluate each option provided in the question. For example, the presence of dry riverbeds and valley networks on Mars suggests erosion patterns consistent with flowing water, which is a strong indicator of past rivers and running water.
3. Step 3: Consider the other options. Large volcanoes like Olympus Mons indicate volcanic activity but do not directly suggest the presence of rivers or running water. Similarly, polar ice caps composed of frozen carbon dioxide and the thin carbon dioxide atmosphere are related to Mars' current climate and composition, not evidence of past water flow.
4. Step 4: Compare the options and identify which one provides the strongest evidence for rivers and running water. Geological features like dry riverbeds and valley networks are direct evidence of water erosion, making them the most relevant choice.
5. Step 5: Conclude that the presence of dry riverbeds and valley networks visible on the Martian surface is the strongest evidence that Mars once had rivers and running water, as these features are consistent with the action of flowing water shaping the landscape.