The neighboring planet Mars, which has a comparable geological history to Earth, has long piqued people's interest. Its proximity to Earth makes it the most visited planet (by robots, at least), and a number of hopeful but flimsy indications that perhaps life once existed there also contribute to this. These encouraging clues range from a rock with a flower-like appearance to the existence of minor electrical storms to the lingering possibility that liquid water still exists on Mars' surface or ever did.
It's plausible that life frequently manifests itself in the cosmos. However, life disappears quickly because it is unable to keep the planet's surface in a habitable state. Our study goes one step farther by demonstrating the entire self-destruction potential of even the most rudimentary biosphere."
Yet the history of life on Mars is the subject of a recent research published in the journal Nature Astronomy. The red planet suffered a huge temperature change when it was younger, one that made it significantly more arid and less wet, as shown by geologic evidence. The aforementioned article argues that climate change, brought on by gaseous emissions from living things, may be the cause of this climactic shift.
Researchers from France and the United States claimed in a study that life may have thrived in Martian regoliths, or loose dust and rock on top of a layer of bedrock, since it would have been saturated with salt water and shielded from cosmic and ultraviolet radiation. Naturally, this would have occurred between 3.7 and 4.1 billion years ago, and the life in issue would have been more akin to Earth microorganisms than anything particularly advanced or sentient. However, these bacteria might have developed to a point where they could have used carbon dioxide and hydrogen, both of which would have been abundant at the time on Mars, and released methane.
We know this because methanogenesis—a process by which bacteria like those generate methane—occurs in hydrothermal vents on Earth. However, because they are in the ocean, not much methane is released into the atmosphere because some of it is absorbed by the water. The following emission of methane may have altered the planet's atmosphere to the point where it eventually turned unfriendly to the hypothetical Martian bacteria because they would not have had that luxury.
The authors state that the methanogenesis-caused alteration in air composition "would have sparked a global cooling event, ending potential early warm conditions, compromising surface habitability, and driving the biosphere deep into the Earth crust." According to them, "lowland sites at low-to-medium altitudes" are the areas where life forms that behaved in this manner would have most likely left traces for humans to uncover in the future, therefore future explorers should focus their efforts there to test their hypothesis.
The life in issue would not have been extremely intelligent or advanced, but would have resembled Earth microorganisms.
People are familiar with the concept of "man-made climate change," according to which emissions from modern civilization, particularly those of carbon dioxide, are gradually changing the planet's temperature. However, it is not impossible for primitive life—possibly even single-celled life—to significantly affect a planet's atmosphere and consequently its climate. In fact, such an event has happened on numerous occasions throughout Earth's history. Algae transformed enough carbon dioxide into oxygen between 2 billion and 2.4 billion years ago to permanently change the composition of the Earth's atmosphere. The formation of the ozone layer, which protects land-based life from harmful ultraviolet rays, was also a result of the Great Oxygenation Event. The future evolutionary history of life on Earth as well as the climate were both significantly altered by both of these occurrences.
The thought of Martian life making its own planet uninhabitable bears an uncanny resemblance to human behavior today, even if the Great Oxygenation Event made Earth more habitable for some life and less habitable for others (especially anaerobic bacteria). The projected effects of man-made climate change include rising sea levels, a spike in pandemics, heat waves that make significant portions of the earth uninhabitable, an increase in wildfires, and other effects that threaten to terminate life as we know it on Earth. The authors of the study were aware of the similarities between the situation on Earth today and one that might have existed on Mars billions of years ago.
The study's principal investigator, astrobiologist Boris Sauterey of the Institut de Biologie de l'Ecole Normale Supérieure (IBENS) in Paris, France, told Space.com that "the building blocks of life are everywhere in the universe." "So it's feasible that life manifests itself frequently in the cosmos. However, life disappears quickly because it is unable to keep the planet's surface in a habitable state. Our study goes a step farther by demonstrating the entire self-destruction potential of even the most rudimentary biosphere."
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