Ancient microbes caused a climate change on Mars that made the planet less habitable, which may have eventually led to their extinction, a new climate modeling study suggests.
According to the study, simple microbes that feed on hydrogen and secrete methane could have thrived Mars about 3.7 billion years ago, around the same time that primitive life was dominant Earthits primordial oceans. But while he was on Earth his appearance simple life gradually created an environment conducive to more complex life forms, the exact opposite happened on Mars, according to a team of scientists led by astrobiologist Boris Sauterey from the Institut de Biologie de l’Ecole Normale Supérieure (IBENS) in Paris, France.
Sauterey and his team conducted a complex computer modeling study that simulated the interplay of what we know about the ancient atmosphere and the Martian lithosphere with hydrogen microbes similar to those found on ancient Earth. The researchers found that while on Earth the methane produced by these microbes gradually warmed the planet, Mars cooled, driving the microbes into deeper and deeper layers of the planet’s crust to survive.
Related: NASA’s Mars Life Explorer mission would dig deep to hunt for life on the Red Planet
Slowing down the greenhouse effect
“At that time, Mars would have been relatively wet and relatively warm, between minus 10 degrees and 20 degrees Celsius [14 degrees Fahrenheit and 68 degrees Fahrenheit]Sauterey told Space.com. “It had liquid water in the form of rivers, lakes and perhaps oceans on its surface. But its atmosphere was quite different from Earth’s. It was just as dense, but richer in carbon dioxide and hydrogen, which acted as powerful heating gases.”
Being further away from sun than Earth and therefore naturally cooler, Mars needed these greenhouse gases to maintain a comfortable temperature for life. But as these early microbes began gobbling up hydrogen and producing methane (which on Earth acts as a powerful greenhouse gas), they actually slowed that warming. the greenhouse effectmaking ancient Mars gradually so cold that it became inhospitable.
“On ancient Mars, hydrogen was a very strong heating gas due to something we call a collision-induced absorption effect where carbon dioxide and hydrogen molecules interact with each other,” explained Sauterey. “We don’t see this on Earth because our planet’s atmosphere is not as rich in carbon dioxide as that of Mars. So the microbes essentially replaced a more powerful warming gas, hydrogen, with a less powerful warming gas, methane. which would have pure cooling.”
It hides deeper
As the planet cooled, more of its water turned to ice and the surface temperature dropped below minus 70 degrees Fahrenheit (minus 60 degrees Celsius), pushing microbes ever deeper into the crust where warmer conditions persist. While at first the microbes may have lived comfortably just beneath the sandy surface of Mars, within a few hundred million years they were forced to retreat to depths of more than 0.6 miles (1 kilometer), the modeling revealed.
Sauterey and his team identified three sites where traces of these ancient microbes would likely have survived closer to the surface. These locations include; Jezero Craterwhere NASA’s Perseverance rover it is currently searching for rock samples that could harbor traces of this ancient life, and two low-lying plains: Hellas Planitia in the mid-latitudes in the southern hemisphere and Isidis Planitia just north of the Martian equator.
“The places on the planet where these microbes would be closest to the surface would be the warmest areas,” Sautery said. “And the warmest places are usually the deepest places. At the bottom of these craters and valleys, the climate is much warmer than the rest of the surface, so it would be much easier to look there for evidence of these forms. life.”
Oasis of habitability
Next, the researchers would like to know if these ancient microbes could still live anywhere within the Martian crust. Satellites have detected in the past traces of methane in the thin atmosphere of Marsbut at present it is impossible to say whether this methane is of biological origin.
“Because the atmosphere of Mars is almost gone these days, these microbes will have to turn to another source of energy,” Sauterey said. “We can imagine that some geological process on Mars today could provide the same type of energy substrate, hydrogen and carbon dioxide, that these microbes could live on. We would like to find out and try to identify any oases of habitability in the Martian crust”.
Is life self-destructive?
The findings, Sauterey added, suggest that life may not have intrinsic self-sustaining properties, as some biologists believe was the case on Earth (until the emergence of humanity). Life, in fact, can emerge randomly in the universeonly to disappear through its own interaction with the host world.
“The ingredients of life are everywhere in the universe,” Sauterey said. “So it’s possible that life appears regularly in the universe. But life’s inability to sustain habitable conditions on the planet’s surface makes it disappear very quickly. Our experiment takes it even a step further by showing that even a very primitive The biosphere can have a completely self-destructive effect.’
The study (opens in new tab) was published in the journal Nature Astronomy on Monday (10 October)
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