‘Life could have existed’: Signs of ancient carbon cycle discovered on Mars

New research being led by a University of Calgary scientist shows Mars was not always cold and barren.

Mars was once wetter and warmer than it is today, according to a new study.

The study, led by a University of Calgary geoscientist, was published Friday.

It found evidence that carbon dioxide from the ancient atmosphere was cycling through the planet’s surface, much like it does on Earth.

• The information you need to know, sent directly to you: Download the CTV News App

“The lessons it offers in terms of our own habitability on Earth are significant,” said lead researcher Benjamin Tutolo. “The fact that the carbon cycle is this really finely balanced system here on Earth and on Mars – it clearly went too far in one direction.”

Tutolo’s paper identifies a functioning carbon cycle on early Mars, based on minerals discovered by NASA’s Curiosity rover.

“I mean, it’s an exceptional opportunity,” said Tutolo. “It’s one of those things that you look forward to that is potentially never happening sometime in your career –- and it’s happening now, which is, to me, one of the most amazing opportunities of my life.”

Tutolo and an international team of researchers analyzed rock samples collected by the rover inside Gale Crater, a massive impact basin that once held a lake.

The rover drilled into sedimentary layers and detected siderite, a type of iron-rich carbonate that forms when carbon dioxide reacts with water and rock under specific chemical conditions.

“It was a complete surprise for everyone on the team whenever we had this observation,” Tutolo said.

“If you go back and look at what we had known about these sediments based on orbital spectroscopy, never, even upon reinterpretation of that data, did anyone consider the possibility that there would be iron carbonate or siderite there.”

The siderite appeared in three separate samples and made up between five and 10 per cent of the rock by weight.

It was found alongside evaporite salts, suggesting it formed as underground water evaporated or dried out.

The water would have needed to be mildly alkaline and low in oxygen, and it likely existed in subsurface spaces not directly exposed to the atmosphere.

Because those conditions are not found on Mars today, scientists say the minerals point to a much more chemically and hydrologically active environment in the past.

Since the mineral-rich layer spans at least 89 metres in thickness, the process that created it must have continued over an extended period.

“Here on Earth, our habitability has been maintained over the last four-billion years or more by our carbon cycle, by the fact that carbon comes out of our volcanos, sticks around in the atmosphere and ultimately gets sequestered,” Tutolo said.

“The fact that we’re able to recycle that so efficiently on Earth has enabled our carbon cycle to be approximately in balance over geologic time, which enabled habitable conditions to exist on Earth.

“On Mars, we know something must have happened to the atmosphere in order to become the cold, dry state that it is today.”

The researchers estimate that similar carbonate-bearing layers across Mars could contain up to six-times the amount of CO₂ that Mars’ atmosphere currently contains.

“We estimate that approximately six or so current Martian atmospheres’ worth of carbon dioxide is contained in those deposits,” Tutolo said. “These deposits represent a sequestration of the Martian atmosphere.”

In some of the analyzed samples, the team found that the siderite had partially broken down and transformed into other iron-bearing minerals.

That transformation would have released the carbon dioxide it once stored, returning it to the atmosphere and partially closing the Martian geologic carbon cycle.

“The conclusion in the paper is that Mars’s carbon cycle was imbalanced,” said Tutolo. “The CO₂ goes down, but the fact that the carbonate is still there three-and-a-half-billion years later means that ultimately much of the carbon must have stayed.”

Although the paper makes no claim about habitability or life, the discovery contributes to the growing understanding of early Mars as a planet that once had water, a thicker atmosphere and long-lived chemical processes – conditions that scientists view as important for assessing whether a planet could ever have supported life.

“The evidence of habitable environments was abundantly clear,” Tutolo said. “We have evidence for rivers flowing into the ancient Gale Crater lake, we have evidence for the ingredients required for life – all present in the same place.”

Tutolo says that while the mission’s goal isn’t to prove the existence of life, it’s to understand if the right conditions were there.

“There’s abundant evidence that life could have existed,” he said. “The question is whether the reactions ever had the chance to take off.”