If there had ever been life on Mars — and that’s a huge “if” — conditions during the planet’s infancy most likely would have supported it, according to a study led by researchers at the University of Arizona.
Dry and extremely cold, with a tenuous atmosphere, today’s Mars is extremely unlikely to sustain any form of surface life. But 4 billion years ago, Earth’s smaller, red neighbor may have been much more hospitable, according to the study, published in Natural Astronomy.
Most Mars experts agree that the planet started out with an atmosphere much denser than it is today. Rich in carbon dioxide and hydrogen, it likely would have created a temperate climate for water to flow in and potentially allow microbial life to thrive, according to Regis Ferrière, a professor in UArizona’s Department of Ecology and Evolutionary Biology and one of the two senior authors on the paper.
The authors do not claim that life existed on early Mars, but if it did, Ferrière said, “our study shows that underground, early Mars most likely would have been habitable for methanogenic microbes.”
Such microbes, which make their living by converting chemical energy from their environment and releasing methane as a waste product, are known to exist in extreme habitats on Earth, such as hydrothermal vents along cracks in the ocean floor. There, they support entire ecosystems adapted to crushing water pressure, near-freezing temperatures, and total darkness.
The research team tested a hypothetical scenario of an emerging Mars ecosystem by using state-of-the-art models of the Martian crust, atmosphere and climate, combined with an ecological model of a community of Earth-like microbes that metabolize carbon dioxide and hydrogen.
On Earth, most hydrogen is trapped in water and does not often occur alone, except in isolated environments such as hydrothermal vents. However, the abundance in Mars’ atmosphere could have provided an ample supply of energy to methanogenic microbes about 4 billion years ago, at a time when conditions were more favorable for life, the authors suggest. Early Mars would have been very different from what it is today, Ferrière said, tending toward warm and wet rather than cold and dry, thanks to large concentrations of hydrogen and carbon dioxide — both strong greenhouse gases that trap heat in the atmosphere.
“We think Mars may have been a little cooler than Earth back then, but not nearly as cold as it is now, with average temperatures most likely hovering above the freezing point of water,” he said. “While present-day Mars has been described as an ice cube covered in dust, we imagine early Mars as a rocky planet with a porous crust, soaked in liquid water that likely formed lakes and rivers, perhaps even seas or oceans.”
That water would have been extremely salty, he added, according to spectroscopic measurements of rocks uncovered on the surface of Mars.
To simulate the conditions that early life forms would have encountered on Mars, the researchers applied models that predict temperatures at the surface and in the crust for a given atmospheric composition. They then combined that data with an ecosystem model they developed to predict whether biological populations would have been able to survive in their local environment and how they would have affected it over time.
“Once we produced our model, we used it in the crust of Mars — figuratively speaking,” said the paper’s lead author, Boris Sauterey, a former postdoctoral fellow in Ferrière’s group who is now a postdoctoral fellow at the Sorbonne. University in Paris. “This allowed us to evaluate how plausible a subsurface biosphere on Mars would be. And if such a biosphere existed, how it would have changed the chemistry of the crust of Mars and how these processes in the crust would affect the chemical composition of the atmosphere.” affected.”
“Our goal was to model the Martian crust with its mix of rock and salt water, diffuse gases from the atmosphere into the ground, and see if methanogens could live with it,” said Ferrière, who is a researcher. joint appointment at Paris Sciences & Lettres University in Paris. “And the answer is, in general, yes, these microbes could have made a living in the Earth’s crust.”
The researchers then set out to find an intriguing question: If life thrived underground, how deep would you have to go to find it? Mars’ atmosphere would have provided the chemical energy the organisms needed to thrive, Sauterey explained — in this case, hydrogen and carbon dioxide.
“The problem is that even on early Mars it was still very cold on the surface, so microbes would have to go deeper into the crust to find habitable temperatures,” he said. “The question is how deep does biology have to go to find the right compromise between temperature and availability of molecules from the atmosphere that they needed to grow? We found that the microbial communities in our models would have been happiest in the uppermost. few hundred of meters.”
By adapting their model to account for how processes occurring above and below the ground affect each other, they were able to predict the climate feedback of the change in atmospheric composition caused by the biological activity of these microbes. In a surprising twist, the study revealed that while ancient life on Mars was initially prosperous, its chemical feedback to the atmosphere would have caused a global cooling of the planet, eventually rendering its surface uninhabitable and allowing life deeper and deeper underground. are driven, and possibly to extinction.
“According to our results, the Martian atmosphere would have been completely changed by biological activity very quickly, within tens or hundreds of thousands of years,” Sauterey said. “By removing hydrogen from the atmosphere, microbes would have drastically cooled the Earth’s climate.”
The surface of early Mars would soon have become glacial as a result of biological activity. In other words, the climate change caused by life on Mars may have contributed to making the planet’s surface uninhabitable very early on.
“The problem that these microbes would have had to deal with then is that the Martian atmosphere has basically disappeared, has completely thinned out, so their energy source would have disappeared and they should have found an alternative energy source,” Sauterey said. “In addition, the temperature would have dropped significantly and they should have gone much deeper into the crust. At this point, it’s very difficult to say how long Mars would have remained habitable.”
Future Mars exploration missions may provide answers, but challenges remain, according to the authors. For example, while they identified Hellas Planitia, a vast plain carved out very early in Mars’ history by an impact from a large comet or asteroid, as a particularly promising place to search for evidence of past life, the site’s topography generates some of Mars’ most violent dust storms, which could make the area too risky to be explored by an autonomous rover.
However, once humans start exploring Mars, such sites could be shortlisted again for future missions to the planet, Sauterey said. For now, the team is focusing its research on modern Mars. NASA’s Curiosity rover and the European Space Agency’s Mars Express satellite have detected elevated levels of methane in the atmosphere, and while such spikes may be the result of processes other than microbial activity, they raise the intriguing possibility that life forms such as methanogens may be involved. have survived in isolated pockets on Mars, deep underground – oases of alien life in an otherwise hostile world.
Underground microbes may have overrun ancient Mars
Boris Sauterey et al, Early Mars habitability and global cooling by H2-based methanogens, Natural Astronomy (2022). DOI: 10.1038/s41550-022-01786-w
Quote: Life may have thrived on early Mars, until it caused climate change that caused its demise (2022, October 16) Retrieved October 16, 2022 from https://phys.org/news/2022-10-life-early-mars- drove -climate.html
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