Final answer:
Scientists think the volcanoes on Mars may still be active based on evidence such as impact craters, the relatively young age of Olympus Mons, and the geological activity of Mars compared to other planets.
Step-by-step explanation:
Scientists think that the volcanoes on Mars may still be active due to several pieces of evidence. Firstly, images taken from orbit show that many of the Martian volcanoes have a fair number of impact craters, suggesting that they ceased activity a billion years ago or more.
However, Olympus Mons, the largest volcano on Mars, has very few impact craters, indicating that its present surface is relatively young, possibly around 100 million years old. Some of the fresh-looking lava flows on Olympus Mons might have formed relatively recently.
Additionally, Mars represents an intermediate case between the Moon, which is geologically dead, and Earth, which still has a molten interior. The fact that Mars has been more active than the Moon, coupled with the presence of the Tharsis bulge and ongoing activity in the Tharsis volcanoes, suggests that Mars may still experience volcanic activity.