Question

Astronomers estimate that the runoff channels seen on Mars must be at least 3.9 billion years old. How do they estimate ages like this? a. by examining radioactive rocks from these channels returned to Earth by robot probes b. by counting impact craters in the regions containing these channels c. by looking for the erosion of these channels by the regular periods of rainfall that occur on Mars even today d. by measuring the height of the region in which the channels occur; on Mars, older regions are always lower in elevation e. guessing

Answer 1

Answer:  b. by counting impact craters in the regions containing these channels

Explanation:

In counting the impact craters in the areas containing the runoff channels in question, scientists are able to infer the ages of these channels.

The logic is simple, the longer these areas have been exposed, the more meteors they would have been hit by to create these craters. Therefore areas with more craters must have been around for longer and using mathematical models, they come up with age estimates.