Researchers discover the power generators of life in the oldest groundwater on earth

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

The results were published in the journal earlier this week nature communication.

“For the first time, we have a glimpse of how energy stored deep in the Earth’s subsurface can be released over time and distributed more widely through its crust,” says Oliver Warr, a senior research fellow in the University of Earth’s Department of Earth Sciences Toronto and first author of the study. “Think of it as a Pandora’s box of helium- and hydrogen-producing energy, one that we can learn how to harness for the benefit of the deep biosphere on a global scale.”

“Ten years ago we discovered billion-year-old groundwater beneath the Canadian Shield — that was apparently just the beginning,” says Barbara Sherwood Lollar, professor in the Department of Earth Sciences at the University of Toronto and corresponding author. “Now, 1.8 miles (2.9 km) below the surface at Moab Khotsong, we have discovered that the extreme outposts of the global water cycle are more widespread than previously thought.”

Uranium and other radioactive elements occur naturally in the surrounding host rocks, which contain 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 so-called radiogenic reactions in the surrounding rocks and fluids.

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 apart water molecules in a process called radiolysis, creating 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 percent of the helium and neon originally produced by the radiogenic reactions were 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,” says Warr. “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 deep within the Earth that can sustain subsurface microbes on a global scale.”

Warr notes that these calculations are critical to understanding how subsurface life is sustained on Earth 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.

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