Gold-uranium mine in South Africa sheds new light on the power generators of life beneath the earth’s surface

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“Think of it as a Pandora’s box of helium- and hydrogen-generating energy, one that we can learn how to harness for the benefit of the deep biosphere on a global scale,” Oliver Warr, research fellow at the University of Toronto and lead author of the study, said in a media statement.

A decade ago, Warr and his colleagues discovered billions-year-old groundwater beneath the Canadian Shield.

“Now, 2.9 kilometers below the surface at Moab Khotsong, we have found that the extreme outposts of the global hydrological cycle are more widespread than previously thought,” said Barbara Sherwood Lollar, corresponding author of the paper.

Sherwood Lollar explained that uranium and other radioactive elements occur naturally in the surrounding host rock, which contains mineral and ore deposits. These elements contain new information about the role of groundwater as an energy generator for chemolithotrophic (or rock-eating) groups of microorganisms previously discovered in the Earth’s deep subsurface.

When elements like uranium, thorium, and potassium decay underground, the resulting alpha, beta, and gamma radiation has ripple effects, triggering radiogenic reactions in the surrounding rocks and fluids.

Krypton never seen before

At Moab Khotsong, researchers found large amounts of radiogenic helium, neon, argon and xenon and an unprecedented discovery of an isotope of krypton – a never-before-seen tracer of this powerful reaction history.

The radiation also breaks up water molecules in a process called radiolysis, producing large concentrations of hydrogen, an essential energy source for subsurface microbial communities deep within the Earth that don’t have access to solar energy for photosynthesis.

Due to their extremely low masses, helium and neon are uniquely valuable for identifying and quantifying transport potentials. While the extremely low porosity of the crystalline bedrock in which these bodies of water are found means that the groundwater itself is largely isolated and rarely mixes, which is attributed to its 1.2 billion-year age, diffusion can still occur occur.

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

The researchers emphasize that the study’s new insights into how much helium is diffusing upwards from deep within the Earth are a crucial step forward as global helium reserves are depleted and the transition to more sustainable resources gathers momentum.

“Humans are not the only life forms that depend on the energy resources of the Earth’s deep underground,” Warr said. “Because the radiogenic reactions produce both helium and hydrogen, we can not only learn about helium reservoirs and transport, but also calculate the hydrogen energy flow from the deep earth that can sustain subsurface microbes on a global scale.”

Warr noted that these calculations are critical to understanding how subsurface life is sustained on our planet and what energy might be available through radiogenic energy on other planets and moons in the solar system and beyond, and provides information about upcoming missions to Mars, Titan, Enceladus and Europa.

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