Four billion years ago, the solar system was still young. The process of creating planets ended, and Asteroid Bombardment They were subjected to it.
Our planet then becomes livable Then, some time later (some tens or hundreds of millions of years), it settled down. Earth’s primitive biosphere was very different from what it is today. Life hasn’t been invented yet PhotosynthesisToday its main source of energy.
These primordial microbes – the common ancestors of all current life forms on Earth – therefore had to survive in the oceans using another energy source: the consumption of chemical species released by the planet’s interior at the level of hydrothermal systems and volcanoes. , Accumulated as gases in the atmosphere.
Microorganisms are called “Hydrogenotropic Methanogens”, one of the oldest life forms in our biosphere, particularly benefited from the atmospheric composition of that time. These microbes feed on CO2 (carbon dioxide) and H2 (dihydrogen), then abundant in the atmosphere (H2 It represents 0.01% to 0.1% of the atmospheric composition, compared to approximately 0.00005% today, and is thus harvested. Sufficient power To colonize the surface of the oceans.
Alternatively, they release large amounts of methane (from which methanogens take their name) into the atmosphere. This powerful greenhouse gas accumulated there, warming the climate, and a sun less bright than today could not by itself maintain temperate conditions on the planet’s surface.
So the appearance of organisms on Earth, through methanogens, was able to participate in the consolidation of the habitat of our planet and the establishment of favorable conditions for the evolution and complexity of the terrestrial biosphere. And then billions of years.
If this is the opportunity for the early evolution of Earth’s habitat, what about the other planets in the Solar System? Take the example of our neighbor, the Red Planet. As we explore Mars, it seems more and more certain that at the same time the red planet is forming, or more specifically, under its surface. Similar environmental conditions For those who allowed methanogens to proliferate in Earth’s oceans.
Martian microbial life in harsh surface conditions (esp to UV radiation Harmful), temperatures compatible with the presence of liquid water, and abundant sources of energy in the form of atmospheric gases that diffuse into the crust.
Therefore, it was only natural that our research team asked the following question: Could what happened on Earth also happen on the Red Planet?
A portrait of Mars before
Four billion years
To answer this question, we combined three models. Our results have now been published in the journal Science Natural Astronomy. First predicted how Volcanoes on the surface of MarsThe internal chemistry of its atmosphere and the escape of certain chemical species into space determine the atmosphere’s pressure and composition. These properties Then determine the climate.
The second model describes Physicochemical properties of the microcrust of Mars: Temperature, chemical composition, presence of liquid water. These are determined partly by surface conditions (surface temperature, atmospheric composition) and partly by internal properties of the planet (internal thermal gradient, degree of porosity of the crust).
These first two models allow us to simulate the surface and subsurface environment of young Mars. However, there are many uncertainties about the main characteristics of this environment (volcanic intensity at the time, thermal gradient of the crust).
To solve this problem, we explore numerous possibilities in the model for what these features could have been, creating a set of scenarios for what Mars might have looked like four billion years ago.
Boris ChateriFProvided by the author|
A third and final model describes the biology of hypothetical Martian methanogenic microbes. This is based on the assumption that the latter would have been similar to terrestrial methanogens, at least from the point of view of their energy requirements. In each of the environmental scenarios created by the previous two models, it allows us to estimate the habitat of our microbes compared to the subsurface environmental conditions on Mars.
If these are viable, the model estimates how many microbes could survive on the Martian surface, along with crustal and subsurface samples, and the impact the atmosphere has on the chemical composition of the crust of this subterranean microbial biosphere. And on climate. By creating a micro-scale and global-scale connection to the biology of methanogenic microbes Climate of MarsThe combination of these three models makes it possible to simulate the behavior of the Martian ecosystem.
Most likely underground life
ManyGeological clues indicate that Liquid water Four billion years ago, water spread over the surface of Mars, creating rivers, lakes and oceans. So the climate on Mars was milder than it is today. To explain such a climate, our surface model estimates that the Martian atmosphere is dense (similar to present-day Earth’s atmosphere) and particularly rich in CO.2 and H2More than Earth’s atmosphere at that time.
This atmospheric environment Especially rich in CO2 Actually H2 The properties of the atmosphere as a particularly potent greenhouse gas are, under the same conditions, more potent than that of CH4. In other words, 1% H2 The Martian climate then warms to more than 1% CH in the atmosphere4.
In some scenarios created by our model, this greenhouse effect is insufficient to create the climate conditions necessary to maintain liquid water on the surface of Mars: the Red Planet would then be covered in ice. Although the potential temperature is deep within the crust, it remains uninhabitable: the surface is locked by ice, CO2 and H2 Atmospheric gases – an essential source of energy for methanogenic life – cannot penetrate the crust.
However, in most of our scenarios, the presence of liquid water on the Martian surface is possible, at least in the warmest regions. In these regions, CO2 and H2 Atmospheres can penetrate the crust. In all of these scenarios, our biological model predicts that methanogenic microbes would have found viable temperatures and had a sufficient energy source to survive in the first hundred meters of the crust.
In short, although we currently have no real evidence of past or present life on Mars, the Martian crust probably had a subterranean biosphere composed of methanogenic microbes four billion years ago.
A brutal cold weather
Could these hypothetical Martian methanogens, like their counterparts on Earth, have warmed their planet’s climate? Our story gets hopeless here. A subsurface biosphere based on methanogenesis would profoundly modify the Martian atmosphere and consume much of its H.2 and release significant amounts of CH4.
Now, as we have seen, H2 In the background of the early atmosphere of Mars, CH is a more potent greenhouse gas4. The origin of methanogenesis on Earth participated in the establishment of a favorable climate, thus stabilizing the terrestrial habitat, by consuming most of the H for methanogenic life on Mars.2 The Martian atmosphere suddenly cooled the climate by several tens of degrees and participated in the expansion of the ice cap.
In areas where there is still no ice on the surface, our microbes would have to go much deeper into the crust to find potential temperatures, thus moving away from their atmospheric energy source. So Mars, under the influence of life, would have been much less receptive than it was initially.
In the 1970s, James Lovelock and Lynn Margulies grew up Gaia hypothesis, according to which Earth’s habitat is maintained through the harmonious and mutual self-regulation of the terrestrial biosphere and planet Earth. We, the human race, are the unfortunate exception to this.
This concept led to the emergence of the idea of the “Gayan disturbance”: it is not the conditions necessary for life that are absent in the universe, but the ability to survive once it arises. Its planetary environment for a long time.
Our study suggests even more pessimism. As the example of methanogenesis on Mars shows, even the simplest life can, under certain conditions, seriously compromise the habitat of its planetary environment. Is it possible, then, that this tendency toward self-destruction limits the proliferation of life in the universe?