Ancient Mars may have had an environment that could have accommodated a subterranean world full of microbes, according to a report by French scientists.

But if they had existed, the researchers say, these tiny life forms would have changed the atmosphere, caused Martian ice ages, and wiped themselves out.

The findings provide a bleak view of the ways of the cosmos. Life — even simple life like microbes — "might actually commonly cause its own demise," said the study's lead author, Boris Sauterey, now a post-doctoral researcher at Sorbonne University.

The results “are a bit gloomy, but I think they are also very stimulating,” he said in an email. "They challenge us to rethink the way a biosphere and its planet interact."

Souteri and his team said they used climate and terrain models to assess the habitability of the Martian surface. The study, published in the journal Nature Astronomy, says that about 4 billion years ago, water flowed on the Red Planet and was more hospitable than it is today.

They surmised that hydrogen-gobbling, methane-producing microbes might have flourished just beneath the surface back then, with several inches (a few tens of centimetres) of dirt, more than enough to protect them against harsh incoming radiation. Anywhere free of ice on Mars could have been swarming with these organisms, according to Sauterey, just as they did on early Earth.

Early Mars' presumably moist, warm climate, however, would have been jeopardized by so much hydrogen sucked out of the thin, carbon dioxide-rich atmosphere, Sauterey said. As temperatures plunged by nearly minus 400 degrees Fahrenheit (minus 200 degrees Celsius), any organisms at or near the surface would likely have buried deeper in an attempt to survive.

By contrast, microbes on Earth may have helped maintain temperate conditions, given the nitrogen-dominated atmosphere, the researchers said.
The French study investigated the climate effects of possible microbes when Mars' atmosphere was dominated by carbon dioxide and so is not applicable to the earlier times, Pahlevan said.

"What their study makes clear, however, is that if (this) life were present on Mars" during this earlier period, "they would have had a major influence on the prevailing climate," he added in an email.