Microbes Found In ‘Dark Biosphere’ May Change How We Search For Alien Life In Mars

Scientists have discovered an unexpected life form that managed to thrive thousands of feet below the Earth’s surface and far from the reach of sunlight.

The organisms, known as cyanobacteria, have been around Earth for billions of years. They were responsible for turning Earth from an inhospitable rock into a green world, as well as helped shape an oxygen-rich atmosphere, laying the groundwork for the emergence of all forms of life.

Cyanobacteria can be found in a diverse range of environments but they typically get at least some exposure to sunlight because they produce their energy through photosynthesis. This is why the discovery of the creatures deep below the surface in total darkness came as a surprise.

In new research, Fernando Puente-Sánchez, from the Spanish Center of Astrobiology, and colleagues reported the discovery of cyanobacteria thriving 2,000 feet deep below the surface of a region known as the Iberian Pyrite Belt in Spain.

This environment, where light is scarce or nonexistent but where life persists, is called “dark biosphere.”

Researchers found that the subterranean microbes were not that biologically different from their light-loving relatives, but they do not have certain features needed for performing photosynthesis. The organisms actually use a different process to produce energy.

Some cyanobacteria may have found themselves unable to gather enough sunlight to complete photosynthesis so they ended up figuring out how to feed themselves.

Puente-Sánchez and colleagues found that large numbers of this organism were clustered near concentrations of hydrogen, suggesting that the microbes managed to stay alive by absorbing hydrogen gas, chemically combining it with oxygen before releasing hydrogen electrons.

How the organisms switched from photosynthesis to chemical subsistence has implications in the current search for alien life on Mars. While the red planet is not the kind of place that life as we know it could thrive, it was earlier in its history.

“It provides a nice example of a test case of organisms that started at the surface and then were able to adapt to deep biosphere life,” Lynn Rothschild, an astrobiologist at NASA’s Ames Research Center in California, told Space.

If the cyanobacteria below the Earth’s surface found a way to survive, it is possible something similar may have occurred with cyanobacteria-like organisms on Mars.

“Our description of this previously unknown ecological niche for cyanobacteria paves the way for models on their origin and evolution, as well as on their potential presence in current or primitive biospheres in other planetary bodies, and on the extant, primitive, and putative extraterrestrial biospheres,” the researchers wrote in their study published in the journal PNAS on Oct. 1.

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