The important question that begs to be answered is whether ancient microbes might still be living in the subsurface of Mars
Mars it may have had abundant microorganisms living just below its surface billions of years ago. But these ancient microbes triggered an Earth-reverse climate change that brought about a Martian Ice Age and made the planet inhospitable to life, causing the microbes to eventually self-destruct. This is the assessment of a new French scientific modeling study.
The study estimates that about 3.7 billion years ago, at a time when Earth’s first microscopic life forms were emerging in its oceans (eventually leading to larger and more complex organisms that followed), Mars probably had a few simple microbes that fed on hydrogen and expelled methane. The interaction of the Martian atmosphere and lithosphere with the methanogenic microbes, according to computer model simulations, had – in contrast to Earth where the environment gradually became more and more hospitable for life – a bad ending.
The researchers, led by the astrobiologist, Boris Sotereof the Faculty’s Institute of Biology Ecole Normale Superieure of Paris, who made the relevant publication in the astronomy journal “Nature Astronomy»estimate that while on Earth the methane produced by similar microbes slowly warmed the planet, on Mars it led to a drop in its temperature, forcing the microorganisms to penetrate deeper and deeper into the subsoil in order to survive.
“At that time, Mars would have been relatively wet and warm, with temperatures between minus ten and 20 degrees Celsius. It had liquid water in the form of rivers, lakes and perhaps oceans on its surface. But its atmosphere would be quite different from Earth’s. It was just as dense but richer in carbon dioxide and hydrogen, both of which acted as powerful warming gases,” Soterre said.
As Mars was further from the Sun than Earth and thus already colder by nature, it needed those microbial “greenhouse gases” to maintain temperatures favorable for life to grow. But as those ancient methanogenic microbes began gobbling up atmospheric hydrogen and massively producing methane, they eventually slowed down the greenhouse effect instead of, as might be expected, accelerating it.
According to Soterre, “on ancient Mars hydrogen was a very strong warming gas due to interaction with carbon dioxide, something we don’t see in Earth’s atmosphere, which is not as rich in carbon dioxide as that of Mars . So the microbes essentially replaced a more powerful climate change gas, hydrogen, with a less powerful one, methane, which ultimately resulted in the temperature drop.”
As the neighboring planet cooled further, more and more of its liquid water turned to ice and its surface temperatures dropped below minus 60 degrees Celsius, pushing the microbes deeper and deeper below the surface, where there was even more heat. According to the model, within a few hundred million years the microbes had been forced to live at depths greater than one kilometer.
The researchers estimate that in only three areas, which had probably remained warmer, microbes may have survived for a long time near the surface: Jezero Crater (where NASA’s Perseverance rover currently operates), Hellas Plain in the southern Martian hemisphere, and another a plain.
The important question that begs to be answered is whether ancient microbes might still be living in the subsurface of Mars. Martian satellites have detected traces of methane in the planet’s current thin atmosphere, but it is so far impossible to say whether this methane is of biological or geochemical origin.
Soterre pointed out that if the findings of his model hold, it shows that life can randomly appear in the universe but also self-destruct through interaction with its environment through a vicious cycle. As he said, “the ingredients of life are everywhere in the universe. Therefore it is possible for life to appear regularly in the universe. But its inability to maintain hospitable conditions on the surface of a planet leads to its disappearance very quickly. Our experiment shows that even a very primitive biosphere can have a completely self-destructive effect.”
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