The number of impact craters on the slopes of Tharsis volcanoes suggests that they have been inactive
A) since Mars formed 4.6 billion years ago
B) for at least a billion years
C) for at least tens of millions of years
D) only for the last few hundred years

Question

Quizplus · Accepted Answer

The number of impact craters indicates that the Tharsis volcanoes have been inactive for at least tens of millions of years, as fewer craters would suggest more recent volcanic activity.

The Number of Impact Craters on the Slopes of Tharsis