Mars, our planetary neighbor with a similar geological history, has long fascinated Earthlings. Part of that is its proximity to Earth – meaning it’s the most visited planet (by robots, at least); and part of that is due to a number of encouraging but faint signs that perhaps life once existed there. These signs of hope run the gamut from a flower-shaped rock; the presence of tiny electrical storms; to the ever-present possibility that liquid water exists somewhere on the Martian surface or perhaps once did.
“It is possible that life appears regularly in the universe. But the inability of life to maintain habitable conditions on the surface of the planet causes it to disappear very quickly. Our experiment goes even further because it shows that even a very primitive biosphere can have a completely self-destructive effect.”
Yet a new paper in the journal Nature Astronomy has an intriguing premise for the history of life on Mars. We know from geological evidence that the Red Planet underwent a significant climate change in its younger years, which made it much more arid and less watery. The reason for this climate change is not well understood, and the aforementioned article suggests that climate change, caused by gaseous emissions from life on Mars, may also have destroyed it.
In a study by French and American researchers, scientists explained that life could have thrived in Martian regoliths (or loose dust and rock above a layer of bedrock) because they would have been permeated salt water and protected from ultraviolet and cosmic rays. Of course, that would have been around 3.7 to 4.1 billion years ago, and the life in question would have looked like earthly microbes rather than anything particularly intelligent or sophisticated. Yet these microbes could have proliferated to a sufficient degree to consume hydrogen and carbon dioxide, both of which would have existed in treasure troves on Mars at the time – and to release methane.
We know this because, on Earth, such microbes already exist in hydrothermal vents, and they too release methane using a process known as methanogenesis. Because they do this in the ocean, however, little methane is released into this atmosphere, as it is absorbed somewhat by ocean water. These hypothetical Martian microbes would not have had that luxury, and the subsequent release of methane may have altered the planet’s atmosphere so much that it eventually became hostile to microbes.
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“The predicted change in atmospheric composition caused by methanogenesis would have triggered a global cooling event, ending potential early warm conditions, compromising surface habitability, and forcing the biosphere deep into the Earth’s crust,” the authors write. They add that, for future explorers to test their hypothesis, they should target “low and mid-altitude plain sites” because these are the regions where life forms that behaved in this way would most likely have left traces. traces for humans to discover them one day. .
The life in question would have looked like earthly microbes rather than anything particularly intelligent or sophisticated.
Humans are familiar with the idea of human-induced climate change, for which there is a scientific consensus that emissions from industrial civilization, particularly carbon dioxide, are slowly changing the temperature of the planet. Still, the idea of simple life, perhaps even single-celled life, altering a planet’s atmosphere to the point of altering its climate isn’t far-fetched. Indeed, at several times in Earth’s history, such a thing has happened. Between 2 billion and 2.4 billion years ago, algae converted so much carbon dioxide into oxygen that they permanently changed the composition of Earth’s atmosphere. The Great Oxygenation Event, as it is known, also led to the creation of the protective ozone layer around the Earth, which shields life on Earth from harmful ultraviolet rays. These two events permanently changed the future evolutionary history of life on Earth, as well as the climate.
But while the Great Oxygenation Event has made Earth more habitable for some life and less habitable for others (especially anaerobic bacteria), the prospect of Martian life rendering its own planet inhospitable bears an uncanny similarity to the behavior of mankind today. Man-made climate change is expected to cause sea levels to rise, increase the number of pandemics, cause heat waves and render large areas of the planet uninhabitable, lead to more wildfires and, by d other means, to destroy life on Earth as we know it. The parallels between Earth’s current predicament and that which might have existed on Mars billions of years ago were not lost on the study’s authors.
“The ingredients of life are everywhere in the universe,” astrobiologist Boris Sauterey of the Institute of Biology at the Ecole Normale Supérieure (IBENS) in Paris, France, who led the study, told Space.com. research. “It is therefore possible that life appears regularly in the universe. But the inability of life to maintain habitable conditions on the surface of the planet causes it to disappear very quickly. Our experiment goes even further because it shows that even a very primitive biosphere can have a completely self-destructive effect.”
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