Life in underground water that has been isolated from the outside for more than a billion years

An investigation reveals how exotic microorganisms survive in water that has been stagnant for about 1.2 billion years at a depth of 2.9 kilometers in South Africa. The findings can also be useful to search for life on other worlds.

The international team of Oliver Warr, from the University of Toronto in Canada, has investigated the aforementioned body of water in a gold and uranium producing mine, specifically the Moab Khotsong mine in South Africa.

The uranium and other radioactive elements naturally present in minerals in and around the mine contain information about the role of groundwater as an energy generator for chemolithotrophic microorganisms, which feed on the stones. This class of microorganisms lives in the deep subsoil of the Earth. When chemical elements like uranium and thorium decay underground, the resulting alpha, beta, and gamma radiation trigger radiogenic reactions in rocks and surrounding fluids.

At Moab Khotsong, researchers found large amounts of radiogenic helium, neon, argon, and xenon. They also made an unprecedented discovery: a never-before-seen isotope of krypton from this complex series of reactions. The radiation also breaks down 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 cannot access the Sun’s energy for photosynthesis.

Oliver Warr collecting a sample at the Moab Khotsong mine. (Photo: Oliver Warr)

Helium and neon are very useful to identify and quantify the potential transport of materials from the subsurface to the surface. Although the very low porosity of the subsurface crystalline rocks in which this water is found means that the groundwater itself is largely isolated and rarely mixes with water from outside, accounting for its 1.2 billion year old, diffusion can still take place.

For example, solid materials such as stone, plastic and even stainless steel end up being passed through by helium. The study results show that diffusion has provided a pathway for 75 to 82 percent of the helium and neon originally produced by radiogenic reactions to be transported through the crust to the surface.

The study results also offer insight into how much vital energy and resources could be made available through the radiogenic pathway to support life in subterranean habitats on the planet Mars and on Saturn’s moons Titan and Enceladus and Jupiter’s Europa.

The study is titled “86Kr excess and other noble gases identify a billion-year-old radiogenically-enriched groundwater system.” And it has been published in the academic journal Nature Communications. (Font: NCYT by Amazings)