Researchers discover life’s energy generators in Earth’s oldest groundwater

An international team of researchers has discovered 1.2 billion-year-old groundwater at a gold and uranium mine in Moab Khotsong, South Africa, shedding more light on how life is sustained below the surface of the Earth and how it can thrive. other planets.

The results were published earlier this week in the journal Nature Communication.

“For the first time, we have a glimpse of how energy stored deep in the Earth’s subsoil can be released and distributed more widely across its crust over time,” said Oliver Warr, associate researcher in the Department of Earth Sciences at the University of Toronto and lead author of the study. “Think of it as a Pandora’s box of helium and hydrogen-producing energy, which we can learn to harness to benefit the deep biosphere on a global scale.”

“Ten years ago we discovered billion-year-old groundwater beneath the Canadian Shield – that was just the beginning, it seems,” says Barbara Sherwood Lollar, a professor in the Department of Earth Sciences at the University of Toronto and corresponding author. “Now, 2.9 km below the Earth’s surface in Moab Khotsong, we have discovered that extreme outposts of the global water cycle are more prevalent than previously thought.”

Uranium and other radioactive elements are naturally present in the surrounding host rock which contains deposits of minerals and ores. These elements contain new information about the role of groundwater as an energy generator for chemolithotrophic (or rock-eating) groups of cohabiting microorganisms previously discovered in the Earth’s deep subsoil. When elements like uranium, thorium and potassium decay underground, the resulting alpha, beta and gamma radiation have ripple effects, triggering what are called radiogenic reactions in rocks. and surrounding fluids.

At Moab Khotsong, researchers discovered large quantities of radiogenic helium, neon, argon and xenon, as well as an unprecedented discovery of a krypton isotope, a never-before-seen tracer of this powerful reaction story. The radiation also breaks up water molecules in a process called radiolysis, producing large concentrations of hydrogen, an essential energy source for Earth’s deep underground microbial communities that are unable to access energy from the sun. for photosynthesis.

Due to their extremely small masses, helium and neon are particularly valuable for identifying and quantifying transport potential. Although the extremely low porosity of the crystalline basement rocks in which these waters are found means that the groundwater itself is largely isolated and rarely mixes, which explains its age of 1.2 billion years, diffusion can always take place.

“Solid materials such as plastic, stainless steel, and even solid rock are eventually penetrated by helium diffusion, much like the deflation of a helium-filled balloon,” Warr explains. “Our results show that diffusion allowed 75-82% of the helium and neon originally produced by radiogenic reactions to be transported through the overlying crust.”

New information from the study on the amount of helium released from deep within the Earth is a crucial step forward, as the world’s helium reserves run out and the transition to more sustainable resources gains momentum, researchers point to. .

“Humans aren’t the only lifeforms that rely on energy resources from deep underground on Earth,” Warr says. “Since radiogenic reactions produce both helium and hydrogen, we can not only learn more about helium reservoirs and transport, but also calculate the hydrogen energy flow of the Deep Earth that can sustain underground microbes on a global scale.”

Warr notes that these calculations are key to understanding how subterranean life is sustained on Earth and what energy might be available from radiogenic energy on other planets and moons in the solar system and beyond, informing future missions. on Mars, Titan, Enceladus and Europa.

Other co-authors on the paper include CJ Ballentine from Oxford University and researchers from Princeton University and the New Mexico Institute of Mining and Technology.