The researchers presented their study this week in the journal Astronomy of nature. Their theory is that microbes changed the planet’s atmosphere and thus triggered an ice age that wiped them out.
The discovery can be said to provide dark perspectives on existence for some. Life – even simple life forms like microbes – “can often cause their own extinction,” says lead author Boris Sauterey. He is a researcher at the Sorbonne University.
– The results are a bit grim, but I think they are also very inspiring. They challenge us to reconsider how the biosphere and the planet affect each other, says Sauterey.
Life underground
Sauterey’s research team estimated how habitable the Martian surface was about 4 billion years ago. To achieve this, they used climate and terrain models. There may have been a lot of water on the planet at that time. Living conditions may therefore have been much more hospitable.
Their conjecture is that microbes that fed on hydrogen and produced methane as a waste product may have flourished. The idea is that this happened a few inches below the ground. If so, it would have provided these microbes with sufficient radiation protection for them to survive.
Wherever there was ice on Mars, these organisms would have spread, in the same way that life on Earth would have spread in its time.
Mars at this time had a thin CO2-rich atmosphere. The humid, hot climate early in Mars history would have reacted strongly to the disappearance of so much hydrogen, Sauterey’s team believes.
Ice Age
Models show that the temperature may have dropped by 200 degrees. Organisms remaining near the surface would have to bury themselves deeply to try to survive.
On Earth, where the atmosphere was dominated by nitrogen, the picture was different. Here the microbes may have helped stabilize the temperature conditions, the researchers believe.
SETI Institute researcher Kaveh Pahlevan says future models of the Martian climate must take the French study into account.
Pahlevan recently conducted another study which concluded that Mars was initially a wet planet. Warm seas have existed there for millions of years, she believes. The atmosphere was therefore denser with a high hydrogen content. Hydrogen may have acted as a greenhouse gas before rising into the atmosphere and disappearing into space.
However, the French study, which focuses on the climate effect of possible microbes, is based on a time when CO2 dominated the Martian atmosphere. Therefore, it is not relevant to the previous period, according to Pahlevan.
What their study makes clear, however, is that if there had been life on Mars during this time, it would have had a major impact on the climate, he says.
Looking for clues
French scientists also have suggestions on where to look for ancient signs of life that could help confirm their theory.
The unexplored area of the Hellas Planita plain is one. The second Jezero crater on the northwestern edge of the Isidis Planita plain, where the Nasa Perseverance spacecraft is currently collecting rock samples. The plan is for these to be brought to earth within a decade.
The next item on Boris Sauterey’s to-do list is also clear: look for signs that microbes are still persistent, in the red plant’s subsoil.
– Is it conceivable that Mars is still inhabited by microorganisms that originated in such a primitive biosphere? And if so, where?
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