Entombed oasis (Image: Greg Taylor/Alamy)

“IT’S BEEN called the Galapagos of the subsurface.” Barbara Sherwood Lollar’s enthusiasm for the fertile watery world her team has found 2.5 kilometres beneath Earth’s surface is palpable. The water circulates through fractures in the rocks of a Canadian copper mine. Dating techniques indicate it has been isolated from the rest of the planet for up to 2.64 billion years – making it a time capsule from the early days of life on Earth.

Better still, it is packed with hydrogen and methane – chemicals that microbes love to eat. “What we have here,” says Sherwood Lollar, a microbiologist at the University of Toronto in Canada, “is a plate of jelly donuts.” While she has yet to confirm whether the water is inhabited, she says the conditions are perfect for life.

The team dated the water using the radioactive decay of elements in the rocks to inert gases. Potassium, for instance, gradually decays to argon. So argon levels in the water help establish how long it has been sitting in the rock fractures, isolated from the rest of the world. This and other proxies suggest the water is between 1.5 and 2.6 billion years old.


Older samples have been found, but all of these are microscopic pockets of water trapped within rocks, not large enough to harbour life. “What is unique about this water is that it has the potential to be an ecosystem,” says Christopher Ballentine of the University of Manchester in the UK, whose lab carried out the dating analyses. “Because there is a large volume of fluid, the water can react with the rock to generate hydrogen and methane. Suddenly, we have all the chemicals to support life,” he says.

The team of microbiologists at the University of Toronto are scanning their water samples for signs of microbial life. Sherwood Lollar says she has a hunch they will find bacteria, but she is almost as excited at the prospect of finding nothing at all.

Water that is 1.5 to 2.6 billion years old is a time capsule from the Precambrian – a period when life was dominated by single-celled organisms. “If future searches do yield [indigenous] microorganisms they would provide enormous insight into the evolution of life on our planet,” says Tullis Onstott at Princeton University.

The water is a time capsule from a period when life was dominated by single-celled organisms

Equally, finding lifeless water would give us an unprecedented window on the primordial soup from which life might have evolved.

“The problem on Earth is that life has dominated for billions of years,” says Sherwood Lollar. “This could be a tiny place where we still have a remnant of the kinds of prebiotic conditions that might have existed on early Earth.” In the long run, Sherwood Lollar hopes to find a whole series of these enclosed water worlds, each from a different period in Earth’s prehistory.

Further afield, she and Ballentine point out that the rocks from the Canadian mine are similar in chemistry and age to rocks in the subsurface of Mars – suggesting fertile conditions could persist inside the Red Planet for millions of years.

This article appeared in print under the headline “The deep, dark lake frozen in time”