A new computer model generated by a team of scientists led by astrobiologist Boris Sauterey from France’s Institut de Biologie de l’Ecole Normale Supérieure (IBENS) suggests that Mars may have once had microbial life. That life’s metabolism could have caused climate change that killed the microbes.
Their work initially assumed the presence of microbes that consumed hydrogen and excreted methane as a waste product. Similar microbes caused Earth to gradually warm up. However, Mars cooled down and could have driven the microbes deeper under Mars’ surface.
Mars used to have a thick, wet atmosphere that had high hydrogen and carbon dioxide content. Earth still has a similar atmosphere, though the “mix” of gasses is different from Mars’, which still has a high carbon dioxide content.
Mars eventually lost most of its atmosphere, especially after its protective magnetic field died. A lot of it got blasted away by solar wind. While it still had a thick atmosphere, though, it could have looked a lot like Earth did before complex life arose. It could even get nearly as warm as what we call “room temperature.”
“Mars would have been relatively wet and relatively warm, between minus 10 degrees and 20 degrees Celsius [14 degrees Fahrenheit and 68 degrees Fahrenheit],” says Sauterey.
That means it could support liquid water on the surface. Most water remaining on Mars is probably frozen at the poles or deep underground. As it was, Mars is farther away from the sun and needed greenhouse gases – mostly hydrogen and carbon dioxide – to maintain a temperature that could have supported life.
As the microbes consumed the hydrogen and produced methane, they could have triggered the cooling effect on the planet. Methane is also a powerful greenhouse gas, but Sauterey says it’s not as powerful as hydrogen can be under the right conditions. Hydrogen can interact with carbon dioxide using the collision-induced absorption effect, which increases its potency as a greenhouse gas.
Methane also typically lasts about a decade, while carbon dioxide can last a couple of centuries. Most methane produced by these early microbes is probably long gone.
As the planet cooled to as low as negative 60 degrees Celsius, it pushed microbes deeper underground than scientific instruments brought by Martian landers like InSight can probe under the Martian surface. (InSight’s instruments are better suited for detecting Marsquakes than finding Martian life anyway, though – in a tribute to their designers – they could detect a bell choir practicing in a nearby building while they were still being tested on Earth.) They might have gone as deep as 1 kilometer under the surface.
Data from Mars probes’ scientific instruments suggest that the ingredients for life are present and the planet once could have served as a good host for life. Some minerals on Mars could only have formed in the presence of liquid water, for instance.
The Viking landers did look for signs of metabolism, but the results were so confusing that most scientists doubt that they found conclusive proof that life exists on modern-day Mars. The instruments could have been contaminated or it turned up only some non-biological chemical activity that sort of looked like the results of metabolism. A few scientists are convinced that they did find proof of life, but maybe the instruments just weren’t advanced enough to provide a definite yes-or-no answer.
Sauterey’s team identified three sites where Martian microbes could still live, including Jezero Crater. The Perseverance rover is still plugging away in Jezero Crater – and extracting exciting data from rock samples that could hold signs of ancient life. Other sites where life might exist include Hellas Planitia at mid-latitudes on the southern hemisphere, and Isidis Planitia just north of the Martian equator.
Yes, life can create climate change naturally.
You will hear a lot about how humans’ industrial activity is pouring a lot of greenhouse gasses into the atmosphere, which can cause climate change. However, that doesn’t mean that life can’t have an impact on the environment just from normal biological activity.
If Mars ever had life, it could have arisen at about the same time as Earth’s earliest known life, about 3.7 billion years ago. The first known life on Earth were anaerobic microbes – they didn’t need a ready supply of oxygen to live. Like Sauterey’s theoretical Martian microbes, Earth’s anaerobic microbes could metabolize hydrogen and produce methane or acetate as by-products of their metabolism.
(It could also be argued that cows also produce methane as a biological “waste product”. However, they still need oxygen to live and don’t account for all the methane that gets leaked into the atmosphere.)
Anaerobic microbes had to do it that way because photosynthesis didn’t exist yet. However, that changed fast when photosynthetic cyanobacteria evolved. These little buggers became the first solar powered life-forms and could split water molecules into their constituent hydrogen and oxygen. Once they became numerous enough, suddenly there was a lot of free oxygen around.
Although that also would have meant that there was a lot more hydrogen around, the anaerobic life-forms just couldn’t handle it. Most of them died off in what was probably Earth’s first mass extinction.
With them went a source of biologically created methane – and, remember, methane is a powerful if short-lived greenhouse gas. This was an early case of a mass extinction (and possible climate change) caused by what would have been considered pollution at the time.
One good part of the evolution of photosynthesis and all the free oxygen it produced was that it made more complex life-forms possible. Oxygen has its downsides, like accelerating aging by doing damage to DNA, but also makes it possible for tissues to become more specialized.
So far, life on Mars hasn’t been confirmed. However, Mars would have once been friendlier toward life than it is now and the presence of anaerobic microbes that can metabolize hydrogen could have explained early climate change.