Mars May Have Had Life Until Climate Change Ended It, New Study Suggests

Mars is increasingly in the viewfinder of planetary scientists, as NASA has made it a goal to send a manned mission to the red planet, sending rovers to its surface and developing technology to prepare for human exploration. The increased focus on Mars has led to some intriguing discoveries—most recently, that life might have existed on the planet before climate change ended it. That's the suggestion of a new study; read on to find out more.

Researchers from the University of Arizona aren't positive there was once life on Mars (in a news release, they call it a "big if"), but they've determined that conditions on the young planet could have supported it. In their study, published in the journal Nature Astronomy, the researchers note that today Mars is dry and freezing cold, seemingly uninhabitable. But four billion years ago, the planet had an atmosphere that was conducive to life—rich in carbon dioxide and hydrogen, which would have allowed water to flow and microbes to flourish.

"Our study shows that underground, early Mars would very likely have been habitable to methanogenic microbes," said Regis Ferrière, a University of Arizona professor and senior author of the paper. These kinds of microbes live by converting chemical energy from their environment and releasing methane as waste. Some of the same kinds of microbes exist in extreme habitats on Earth, such as hydrothermal vents along fissures in the ocean floor. 

"The research team tested a hypothetical scenario of an emerging Martian ecosystem by using models of Mars' crust, atmosphere and climate, coupled with an ecological model of a community of Earthlike microbes metabolizing carbon dioxide and hydrogen," the university said in a news release. They determined that about 4 billion years ago, Mars' atmosphere contained a high amount of hydrogen, which would have allowed methanogenic microbes to thrive. The planet was warm and wet then, with an atmosphere that also contained carbon dioxide. Both hydrogen and carbon dioxide are "greenhouse gases" that trap heat. 

"We think Mars may have been a little cooler than Earth at the time, but not nearly as cold as it is now, with average temperatures hovering most likely above the freezing point of water," said Ferrière."While current Mars has been described as an ice cube covered in dust, we imagine early Mars as a rocky planet with a porous crust, soaked in liquid water that likely formed lakes and rivers, perhaps even seas or oceans."

Creating a model of Mars' early crust, then applying gases from its atmosphere, the scientists found that microbes could have lived in the planet's crust, most likely in the upper few hundred meters. Unfortunately, the gases those microbes produced likely brought about their destruction, the scientists say.

The study found that the microbes' "chemical feedback to the atmosphere" caused the planet to cool, making its surface uninhabitable and driving life deeper underground, ultimately leading to its extinction. "According to our results, Mars' atmosphere would have been completely changed by biological activity very rapidly, within a few tens or hundreds of thousands of years," said the study's first author, Boris Sauterey of the Sorbonne. "By removing hydrogen from the atmosphere, microbes would have dramatically cooled down the planet's climate." In other words, climate change may have turned Mars into the barren planet it is today.