Microbes living hundreds of feet below seafloor and using minimal energy may answer whether Mars has life: Study
The deepest part of the oceans is home to organisms that get by with the least amount of resources. According to estimates from a new study, microorganisms residing beneath the seafloor can survive with fifty quintillion times lesser energy than a human. The findings could shed light on the origin of life on Earth and the potential for life elsewhere in the solar system.
These microorganisms take refuge in ocean sediments buried under the seafloor, which are either rock materials carried from the land to the sea, volcanic materials, or meteorites that landed from space. But the oxygen levels in these regions is limited: it is present in less than 3% of sediments. Still, the microbial inhabitants manage to stay afloat.
Exploration of the subsea surface showed that microbes there survive with minimal energy for long periods. More recently, scientists awakened microorganisms trapped in 100-million-year-old sediments, buried 245 feet under the seafloor of the South Pacific Gyre from their slumber. The region, called ocean desert, sits between Australia and South America.
"All life needs energy," Dr James Bradley, Lecturer in Environmental Science at the Queen Mary University of London, told MEA WorldWide (MEAWW). It helps organisms stay active and reproduce. But their calculation suggests residents beneath the seafloor are likely inactive, requiring energy only for maintenance and repair. They are neither growing, multiplying, nor evolving.
However, information about them comes from just a few specific sites and studies. "The rest of the subseafloor biosphere is essentially a black box — even though it comprises as many cells as are contained in the Earth's soils, or oceans," Dr Bradley said. So the researchers set out to understand the energy demands of life in such inhospitable regions across the globe.
To calculate the energy consumed by the microbes, Dr Bradley and his team modeled conditions by using data from years of ocean exploration, including information on the distribution and amounts of carbon and microbial life.
"We calculate that the vast majority of microbes contained in global marine sediments can survive on less energy than we ever thought would be capable of supporting life," Dr Bradley explained. They could make do with fifty-billion-billion times less energy than a human. People, on average, use around 100 watts of power, which is roughly equivalent to the power of a ceiling fan, a sewing machine, or two standard lightbulbs.
These findings widen the range of habitable space for microbes on Earth and elsewhere. "The knowledge that microbes can persist on Earth over very long timescales, using very little energy, perhaps raises the possibility that if life had arisen, for example, on Mars — when it had abundant liquid water at its surface — there might still be remnants of that past life surviving in the planet's subsurface," he explained.
The study, which calculated the amount of energy these organisms are using, does not reveal what they specifically do with it. "Exactly how these microbes survive on such little energy is still largely unknown," Dr Bradley said. The study was published in Science Advances.