Liquid lessons: What can we learn from the world’s oldest water?
No, you can’t drink it. The oldest water discovered on Earth has been stagnating underground for 1.6 billion years and is definitely older than your immune system. It predates Mount Everest, was around before the dinosaurs. It’s 10 times saltier than seawater. It smells like rotten eggs. And it’s Barbara Sherwood Lollar’s pride and joy.
The geologist from Canada’s University of Toronto studies microbes and fluids trapped in ancient fractures in the Earth’s crust. Her research goes literally deep, to gold mines in South Africa, caves across Scandinavia, and to the Precambrian Canadian Shield, a mineral-rich landmass that once formed the ocean floor and now holds some of the oldest rocks on Earth. But it’s her discovery of the prehistoric water, 2.4 km down a Canadian mine, that’s exciting everyone from climate scientists to astronomers.
It didn’t happen overnight. Sherwood Lollar, 58, tells Wknd that she had previously found untouched pools inside gold mines in Africa, and knew from the microbial systems they harboured that they’d been cut off from the surface for millions of years. “As scientists, we asked the next question: If we go to a similar geologic setting, but one where rocks were less disturbed, well preserved, how old might the waters be there?”
The team headed to the ancient rocks of Ontario’s Kidd Creek mine in 1992, peering closely at the copper and zinc deposits, “following our noses for the ‘musty’ scent,” of the super-saline waters collected in the fissures. It took 17 years to collect the briny samples that would make history. The team knew they’d found something old. But how do you test how long water has been lying around?
Water, it turns out, accumulates gases like helium and xenon over time, in a way that surface water doesn’t. In it, microbes feast on hydrogen and sulphate, surviving without sunlight the way they do in hydrothermal vents on the ocean floor. If the microbes keep chomping long enough, they turn their watery home saltier and saltier.
By 2013, the team knew that the mine water was at least a billion years old. “It pushed back our understanding of how old flowing water could be in the deep crust of the planet,” Sherwood Lollar says.
Last month, researchers at Oxford university confirmed that the samples collected in 2009 are older even than Sherwood Lollar believed. At 1.6 billion years old, the water holds secrets that science is only beginning to uncover. “Recent studies by our group and others really ‘open the box’ about possible models for planetary habitability,” she says.
Many are keen to use the samples in comparison studies to track human impact on the environment. Others are studying how life thrives in the deep pockets of Earth that don’t ever receive sunlight. Radiolysis (in which radiation breaks down the water molecule to produce hydrogen) might just disprove the accepted theory that a planet needs photosynthesis to be habitable; underground radioactivity might fuel life too. “Our most recent paper shows that organic carbon can be produced as well,” explains Sherwood Lollar.
Could similar pockets of old water exist in other parts of the world? “Absolutely!” she says. Sherwood Lollar likens Earth’s crust to “a Swiss cheese”. Gaps in rocks and water-rock reactions offer rich opportunities for life to thrive undisturbed. “The rocks of South India would be an ideal target for future studies as they are very likely to have the same phenomenon.”
Water from this planet could unlock answers about other planets too. “The vast majority of the Mars crust is continental rock that is billions of years in age, like the Canadian Shield, South Africa and the rocks of southern India,” Sherwood Lollar says. “All these Earth settings are ideal analogues for the rocks of Mars.” If sunless underground pools already support life here, perhaps they do on Mars, and even on the ocean-world moons of Saturn and Jupiter. And maybe we do have neighbours after all, even if they’re a little salty.
Meanwhile, in Odisha… A gem of a discovery from an early Earth
In 2018, a rock sample taken eight years previously from Champua, an Odisha town near the border with Jharkhand, had scientists cheering for India. Studies indicated that grains of magmatic zircon embedded within it were 4.2 billion years old. This would make it the world’s second-oldest sample of its kind, after a rock with a 4.4 billion-year-old zircon fragment found in Western Australia in the 1990s.
For geologists, Odisha’s zircon crystals, not much wider than a strand of hair, are a time capsule. They’re dense and resistant to chemical, geological and temperature changes, adding rings of additional zircon around the original crystal over time, like tree rings.
The crystals are a gateway to understanding the crucial half-billion years after the planet was formed, when it was mostly a ball of cooling lava, minerals and chemical-rich water, long before the first rocks formed 3.9 billion years ago. The crystals are also being studied to determine when the water and an atmosphere would have emerged, making Earth hospitable to life.
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