Look at the moon today and you'll see a barren rock, but that might not always have been the case. It might be difficult to believe, but there was a time-- between 3.5 and 4 billion years ago-- when the moon may have had an atmosphere, pools of liquid water, and possibly even life.

According to new research recently published in the journal Astrobiology, conditions on the lunar surface would have been sufficient to support simple lifeforms shortly after the moon formed from a debris disk 4 billion years ago, reports Phys.org. Volcanic activity on the moon, which peaked 3.5 billion years ago, could have left a window for life to develop there of hundreds of millions of years.

Even more compelling, we know that simple lifeforms were already plentiful on Earth 3.5-3.8 billion years ago. So the moon very well could have been seeded with life from Earth during this period.

"If liquid water and a significant atmosphere were present on the early moon for long periods of time, we think the lunar surface would have been at least transiently habitable," said Dirk Schulze-Makuch, one of the study's researchers.

Recent space missions have shown that water ice is more plentiful on the moon than previously thought. For instance, 2009 and 2010 missions discovered hundreds of millions of metric tons of water ice hiding on the Moon, and there is strong evidence that the lunar mantle also harbors a large amount of water.

It's intriguing to imagine the moon as a thriving oasis billions of years ago, with flowing streams, hot springs, and a denser atmosphere. It's even more interesting to think of what we might learn about early life on Earth by studying moon fossils. That is, assuming they exist.

"There could have actually been microbes thriving in water pools on the moon until the surface became dry and dead," said Schulze-Makuch.

Of course, the only way to know for sure about the possibility of life on the moon is to go there and engage in aggressive exploration. There are no plans to look for ancient organisms on the lunar surface at this time, but perhaps future research will entice such a mission.

At the very least, if the moon did harbor life, it raises the odds of finding it elsewhere in the solar system as well. And that's an exciting prospect.