There's still no proof there was ever life on Mars, but evidence is starting to pile up that conditions were once ripe for life to begin, NASA scientists say.

The Curiosity rover's exploration of the Gale Crater has found signs that liquid water flowed on the planet's surface for tens of millions of years, CNET reports, giving life (of the microbial kind at least) much longer to get going than researchers had previously believed.

The rover had already determined that the planet once had the right chemical ingredients for life, reports the Guardian, and sediment deposits have now revealed that lakes and rivers were once common on its surface, with large amounts of water remaining underground even after those dried up.

Curiosity team members say the new findings suggest that early Mars was much like early Earth. "What I get excited about is imagining a Mars 3.5 to 4 billion years ago, a planet with a thick atmosphere, maybe a blue sky with puffy clouds and mountains and lakes and rivers," John M.

Grunsfeld, a NASA science administrator, tells the New York Times. Grunsfeld, who's also a former astronaut, says the Curiosity mission has given vital clues to how and where to search for evidence of Martian life.

"We don't know if life ever started on Mars, but if it did, we now have a better chance of discovering it," he says. (In other space news, why is SpaceX hiring a farmer?)

This article originally appeared on Newser: Rover Finds More Clues to Martian Life

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