Evolution: some extremophiles use radioactivity (Evolution)

by David Turell , Monday, May 24, 2021, 19:47 (1277 days ago) @ David Turell

The only way they can live:

https://www.quantamagazine.org/radioactivity-may-fuel-life-deep-underground-and-inside-...

"Scientists poke and prod at the fringes of habitability in pursuit of life’s limits. To that end, they have tunneled kilometers below Earth’s surface, drilling outward from the bottoms of mine shafts and sinking boreholes deep into ocean sediments. To their surprise, “life was everywhere that we looked,” said Tori Hoehler, a chemist and astrobiologist at NASA’s Ames Research Center. And it was present in staggering quantities: By various estimates, the inhabited subsurface realm has twice the volume of the oceans and holds on the order of 1030 cells, making it one of the biggest habitats on the planet, as well as one of the oldest and most diverse.

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"Two papers appearing in February by different research groups now seem to have solved some of this mystery for cells beneath the continents and in deep marine sediments. They find evidence that, much as the sun’s nuclear fusion reactions provide energy to the surface world, a different kind of nuclear process — radioactive decay — can sustain life deep below the surface. Radiation from unstable atoms in rocks can split water molecules into hydrogen and chemically reactive peroxides and radicals; some cells can use the hydrogen as fuel directly, while the remaining products turn minerals and other surrounding compounds into additional energy sources.

"Although these radiolytic reactions yield energy far more slowly than the sun and underground thermal processes, the researchers have shown that they are fast enough to be key drivers of microbial activity in a broad range of settings — and that they are responsible for a diverse pool of organic molecules and other chemicals important to life.

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"In work published in 2016, they showed that radiolytic hydrogen peroxide was likely interacting with sulfides in the walls of a Canadian mine to produce sulfate, an electron acceptor. But Sherwood Lollar and her colleagues still needed proof that cells were relying on that sulfate for energy.

"In 2019, they finally got it. By culturing bacteria from the groundwater in mines, they were able to show that the microbes made use of both the hydrogen and the sulfate. Water, some radioactive decay, a bit of sulfide — “and then you get a sustained system of energy production that can last for billions of years … like an ambient pulse of habitability,” said Jesse Tarnas, a planetary scientist and NASA postdoctoral fellow.

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"Analyses of water samples from the same Canadian mine showed very high concentrations of acetate and formate, organic compounds that can support bacterial life. Moreover, measurements of isotopic signatures indicated that the compounds were being generated abiotically. The researchers hypothesized that radiolytic products were reacting with dissolved carbonate minerals from the rock to produce the large quantities of carbon-based molecules they were observing.

"To cement their hypothesis, Sherwood Lollar’s team needed additional evidence. It arrived just one month later. Nuclear chemists led by Laurent Truche, a geochemist at Grenoble Alpes University in France, and Johan Vandenborre of the University of Nantes had been independently studying radiolysis in laboratory settings. In work published in March, they pinned down the precise mechanisms and yields of radiolysis in the presence of dissolved carbonate.

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"According to their models, in deep sediments more than a few million years old, radiolytic hydrogen is being produced and consumed more quickly than organic matter is — making radiolysis of water the dominant source of energy in those older sediments. While it accounts for only 1%-2% of the total energy available in the global marine sediment environment — the other 98% comes from organic carbon, which is mostly consumed when the sediment is young — its effects are still quite sizable. “It might be slow,” said Doug LaRowe, a planetary scientist at the University of Southern California, “but from a geologic perspective, and over geologic time … it starts to add up.”

"This means that radiolysis “is a fundamental source of bioavailable energy for a significant microbiome on earth,” Sauvage said — not just on the continents but beneath the oceans, too. “It’s quite striking.”

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"Modeling and experimental work have shown that even simple systems (consisting solely of hydrogen, carbon dioxide and sulfate, for example) can lead to extremely intricate microbial food webs; adding compounds like formate and acetate from radiolysis to the mix could significantly broaden the potential ecological landscape. And because acetate and formate can form more complex organics, they can give rise to even more diverse systems. “It’s important to see life operating with this amount of complexity,” said Cara Magnabosco, a geobiologist at the Swiss Federal Institute of Technology Zurich, “even in something that maybe you would view as very simple and very energy-poor.'”

Comment: Back to the same concept. Life must have a continuous energy supply to survive. Further this system may be the way life started.