(ORDO NEWS) — Life on Mars, if it was there after all, may have destroyed itself, writes Scientific American. And even if microorganisms can make the planet uninhabitable, then intelligent beings will cope with this task faster, scientists warn.
While we already know that Mars used to be a wetter, warmer, and more habitable place than the parched desert it is today, researchers have yet to find conclusive evidence that the planet once hosted life.
If there really was life there, then important questions arise before us: how did living beings influence the planet, and where can we find evidence of their existence?
Data from a new study designed to answer these questions show that, contrary to common sense, the biosphere of Mars – if it really existed – could have significantly contributed to the transition of the planet to its current uninhabited state.
These studies also allow us to highlight some regions – including the Lake Lake crater, where NASA‘s Perseverance rover is currently operating, – which are best suited to search for traces of life. However, they also suggest that life on Mars could be its own worst enemy.
Using climate and terrain models to recreate the appearance of Mars as it was four billion years ago, French researchers concluded that during that period, microorganisms may have safely existed only a few centimeters below the surface of the Red Planet, and from a strong cosmic radiation they were protected by a layer of soil.
However, this underground biosphere at some point, to its misfortune, began to go deeper and deeper, to which it was pushed by low temperatures, which became the result of its vital activity.
The authors of the study, suggested that these hypothetical ancient microorganisms absorbed hydrogen and carbon from the Martian atmosphere and produced methane.
All three of these substances act as heat-trapping greenhouse gases, that is, changes in the concentration of each of them can have a significant impact on the temperature on the surface of the planet.
In this case, the decrease in the levels of greenhouse gases produced by these hypothetical “methanogenic” microorganisms in the atmosphere of Mars provoked a global cooling, as a result of which most of the planet was covered with ice, and it eventually turned into an uninhabited desert.
“In fact, we are arguing that life, appearing on the planet in its certain form, can be self-destructive,” said Boris Sauterey, a research fellow at the Sorbonne University in Paris and lead author of the study. “It is this tendency to self-destruct, perhaps limits the ability of life to arise everywhere in the universe.”
Blessing of Gaia or Curse of Medea
In 1965, the late chemist James Lovelock, then at NASA’s Jet Propulsion Laboratory, formulated a viable strategy for discovering life on other planets.
Lovelock and his fellow researchers have argued that certain chemical compounds in the planet’s atmosphere serve as so-called biosignatures that indicate the presence of life.
On Earth, for example, the coexistence of methane (produced by methanogens) and oxygen (produced by photosynthetic organisms) is a powerful biosignature.
The thing is that under environmental conditions, both gases eliminate each other, so the constant presence of both indicates their continuous replenishment, which also occurs from biological sources.
The idea that living organisms directly influenced the chemistry of the Earth’s atmosphere became the basis for what Lovelock called his “Gaia Hypothesis,” which he developed with microbiologist Lynn Margulis in the 1970s.
The Gaia Hypothesis, named after the ancient Greek goddess of the earth, states that life is a self-regulating system. Terrestrial organisms interact collectively with their environment in such a way that the habitability of their environment in this case, the planet itself is maintained.
For example, rising global temperatures due to excess carbon dioxide in the atmosphere can also stimulate the growth of plants, which in turn take more greenhouse gases from the air, ultimately cooling the planet.
In 2009, paleontologist Peter Ward of the University of Washington offered a less optimistic view. On a planetary scale, the scientist argued, life is more self-destructive than self-regulating, and eventually destroys itself.
In contrast to the Gaia hypothesis, he named his idea after another character from Greek mythology – Medea, a mother who kills her own children. To argue for the “Medea hypothesis,” Ward cited several episodes of mass extinction on Earth as examples that may indicate the self-destructive nature of life.
On the eve of the Great Oxygen Catastrophe more than two billion years ago, photosynthetic cyanobacteria emitted huge amounts of oxygen into the Earth’s atmosphere, which until then had practically no this highly active gas.
This inevitably led to the extinction of the former owners of the planet – methanogens and other “oxygen-free” organisms, for which oxygen was poisonous.
“Just look at the history of the Earth and you will see periods when life turned out to be its own worst enemy,” Ward said, commenting on the obvious connection between his Medea hypothesis and the study of Soterey and his colleagues. “I think that the same story could take place and on Mars”.
And in the spirit of the Gaia hypothesis, this event, which became completely catastrophic for anoxic life forms on Earth, served as a catalyst for the flourishing of other microorganisms: the influx of atmospheric oxygen played a key role in ensuring the biological diversity of our planet and in the appearance of the multicellular ancestors of our modern biosphere.
Thus, determining whether life follows the trajectory of Gaia or Medea is perhaps only a matter of perspective and requires a wider interplanetary viewing angle.
But until scientists discover life on other planets, we can only rely on speculative comparisons obtained through theoretical studies such as Sauterey’s work.
A more thorough search for life on Mars
Kaveh Pahlevan, a research fellow at the SETI Institute, says Sauterey’s study, which he did not participate in, “really expands our understanding of the impact of the biosphere on habitability.” But he also noted that the study looked at the impact of only one type of metabolism on the planet.
For example, it does not take into account the full complexity of events such as the Great Oxygen Catastrophe, which occurred as a result of the conflicting influence of methanogens and cyanobacteria.
Sauterey acknowledges this possible shortcoming: “It can be assumed that a more complex, more diverse biosphere [on Mars] would not have such a negative impact on the habitability of the planet as the effect that only methanogens could have,” he noted.
However, this limitation of the researchers’ conclusions may in itself point to one fundamental truth.
The abundance of diverse micro-organisms on ancient Earth and the resulting evolutionary flexibility to recover from catastrophic environmental changes is likely why the complex terrestrial biosphere managed to survive, while the supposedly simpler biosphere on Mars simply disappeared.
According to Ward, the increase in diversity is likely to have helped the biosphere avoid the sad fate of the curse of Medea.
“I truly believe that the only way out – the only way to keep life on the planet when it appears there – is the development of intelligent life forms,” Ward said. Only then, according to him, can technological solutions appear that will mitigate ”
As part of their study, scientists did not consider the possibility of the existence of modern methanogens hiding in the Martian interior.
Their likely presence could help explain the mysterious plumes of methane that scientists have repeatedly recorded in the planet’s atmosphere (although they may also be caused by inanimate processes).
As for ancient Mars, as part of the study, scientists noted those places on the planet where hypothetical microorganisms could live closer to the surface (that is, be within the reach of perfect devices that can detect their traces).
These “hot spots” coincide with those rare areas of Mars that could remain ice-free for much of the planet’s history, despite near-global glaciation as a result of global cooling. One such site is the Lake Crater, the site of an ancient lake and a vast delta where fossils can remain.
By a happy coincidence, this is where NASA’s Perseverance rover is currently operating, which is extracting materials potentially containing biosignatures for further analysis in laboratories on Earth.
However, it is not clear whether it will be possible to detect traces of ancient methanogens there. They may be buried under deep layers of sediment that the Perseverance rover cannot penetrate.
In addition to the Jezero crater, scientists name two even more promising areas where traces of ancient methanogens may be found: the Hellas Plain and the Isis Plain.
This increase in the number of likely targets indicates a growing interest in the Martian surface, which could lead to an expansion of the search for life on this planet.
Victoria Orphan, a geologist at the California Institute of Technology, who was not involved in the study, explains this. According to her, Sauteray’s work is “a starting point that helps stimulate debate and deepen thinking about future missions.”
“However, of course, all this is just a hypothesis, and therefore everything is ambiguous,” Soterey admitted. “We can only say that with some degree of probability in this particular region of Mars its crust was habitable.”
According to him, the fact that Mars was once inhabited does not mean at all that someone really lived on this planet.
Whether ancient methanogens lived on Mars or not, the results of the new study serve as a reminder that living organisms can create the conditions for their own prosperity – or extinction.
Even single-celled organisms have the ability to turn a completely habitable planet into an uninhabitable place. And, as Sauteray added gloomily, “with modern technological means at their disposal, people can do it much faster.”
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