1.2 billion-year-old groundwater is some of the oldest on Earth

Groundwater that was recently discovered deep underground in a mine in South Africa is estimated to be 1.2 billion years old. Researchers suspect that the groundwater is some of the oldest on the planet, and its chemical interactions with the surrounding rock could offer new insights about energy production and storage in Earth's crust.

In fact, Oliver Warr, a research associate in the department of Earth sciences at the University of Toronto in Canada and lead author of a new study about the groundwater discovery, described the location in a statement as a "Pandora's box of helium-and-hydrogen-producing power."

The South African groundwater was also enriched in the highest concentration of radiogenic products — elements produced by radioactivity — yet discovered in fluids, according to the study, demonstrating that ancient groundwater sites may one day potentially serve as energy sources.

The gold and uranium mine, known as Moab Khotsong, sits about 100 miles (161 kilometers) southwest of Johannesburg and is home to one of the world's deepest mine shafts, plunging to depths of 1.86 miles (3 km) below the surface at its deepest, according to the mine (opens in new tab).

The new find follows the prior discovery of approximately 1.8 billion-year-old groundwater made during a 2013 research expedition (also led by Warr). That finding occurred at Kidd Creek Mine in Ontario, which lies beneath the Canadian Shield, a geologic structure comprised of igneous and metamorphic rock dating to the precambrian supereon (4.5 billion to 541 million years ago). The Canadian Shield spans 3 million square miles (nearly 8 million square km), and Warr referred to it as a "hidden hydrogeosphere" — an abundance of hydrogen — in a blog post (opens in new tab) published July 5.

"One of the most exciting parts about this new discovery is that at first we thought the groundwater at Kidd Creek was an outlier," Warr told Live Science. "But now we have this brand-new site located somewhere different with a completely different geologic history that also preserves fluid on a billion-year timescale. It looks like this is a feature of these environments, which represent about 72% of the total continental crust by surface area."

Until now, "We only had one data point, and it's pretty hard to say that, yes, this is applicable to the entire world," Warr said. "But this new site reaffirmed what we considered to be true: that these systems trap water over extremely long time spans."

Warr described the way that rocks release this billion-year-old groundwater as similar to the way that liquid escapes from a water balloon.

"These deep mines are the perfect location for what we do, since, as researchers, we don't have the time or the money to put a hole in the ground, but that's what a mine does. When they drill bore holes, the water that has been trapped inside the rock starts gushing out — it's like piercing a water balloon — and we're able to capture it."

After collecting the samples at Moab Khotsong, Warr and his team of international researchers examined their contents and found that the water contained properties that resembled those of water at Kidd Creek.

"In these deep settings, water is held in cracks in the rock and, over time, they interact, resulting in uranium, which then decays over millions, and even billions, of years, creating noble gases," Warr said. As these noble gases accumulate in the water, researchers can measure their concentrations and how long they were present within the rock.

Warr explained that the samples collected contained high salt content — about eight times more than that of seawater — as well as concentrations of uranium, radiogenic helium, neon, argon, xenon and krypton. They also found the presence of hydrogen and helium, both of which are important energy sources. This finding offers a previously unseen glimpse of helium diffusion from deep within the planet, an important process to consider as we face an ongoing helium shortage, and could hint at energy production under the surface of other planets, too, according to the study.

"As long as there is water and rock, you'll see the production of helium and hydrogen — and that doesn't necessarily mean this has to be taking place only on Earth," Warr said. "If there is water on the subsurface of Mars or any other rocky planet, helium and hydrogen could be generated there too, leading to yet another energy source."

The findings were published June 30 in the journal (opens in new tab)Nature Communications (opens in new tab).

Originally published on Live Science.

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