There, however, the activity appears to have stopped operating early in the planet's history, billions of years ago. On our moon, too, volcanism operated early and then shut off sometime around 3 billion years ago. Another possibility, McEwen says, is ice volcanism. Some researchers have also suggested that the same sort of ice volcanism may be present on Saturn's moon, Enceladus. Io, one of Jupiter's moons.
Planetary scientists have no doubt that Jupiter's moon Io is volcanically active.
As many as 500 volcanic centers may have been active in the last 100 years. This is what happened on Earth during the Archean era, 2.5 billion years ago, when the Earth was hotter. That's interesting, because it suggests that we might learn something about ancient volcanoes on Earth by studying Io today.