Deep rocks have been cracked open and water isolated for billions of years released – the liquid may represent Darwin's “warm little pond” where life arose
IT IS the closest we have ever come to finding Earth's primordial soup. Ancient rocks deep underground contain water that has been locked away for billions of years. It may never have been touched by life.
In 2007, geochemist Barbara Sherwood Lollar at the University of Toronto in Canada and her team found treasure in a copper mine. Water gushing out of cracks in the rock, caused by mining, turned out to be over a billion years old. Now the group has made a similar find in a second mine, suggesting ancient rocks could be riddled with such time capsules, right back to the early days of life on Earth.
Sherwood Lollar's team is now scouring the water for ancient forms of life, perhaps unknown to science. So far it seems it holds no life, but that is just as exciting because it means the water they found may be identical to that in which life began.
If that's the case, it opens up an extraordinary opportunity to understand how life got started on Earth, and where (see "Beginner's guide to the origin of life"). The find could also offer insights into how life may survive on other planets.
Sherwood Lollar first got a whiff of the hidden water over a decade ago, deep inside the Kidd Creek Mine in Timmins, Ontario, Canada. In a corridor more than 2 kilometres beneath the surface, she caught a whiff of gas from a fracture in the rock. Water dripped from the hole. Subsequent analyses revealed it to be between 1.1 and 2.7 billion years old (Nature, doi.org/tgw). The smell came from the sulphurous gases mixed in with the water, which also holds methane and hydrogen.
Crucially, as far as the team could tell, the water contained no trace of life. "It speaks to this question of whether we can find an exotic small part of this planet that has not been touched by life," says Sherwood Lollar. "These fractures may have been isolated long enough that they retain chemistry that reflects the same kind of processes that were taking place before there was life on Earth. At that time, presumably the whole planet would have looked something like this."
The discovery could have been a one-off, so the team has been looking for other places where ancient water exists in deep rocks. Last month at the Goldschmidt conference in Sacramento, California, team member Chelsea Sutcliffe presented their results from two mines in the Sudbury basin, also in Ontario.
Like Timmins, the mines are dug into rock that is billions of years old. Sutcliffe collected water from 1.3 and 1.7 kilometres down, and so far it looks very similar to the Timmins water. The chemicals in the water are similar, and isotope ratios suggest it is similarly old. The team are now running further analyses: the noble gases in the water samples will provide a fairly precise age.
"If they are seeing the same thing at Sudbury, that's pretty powerful," says Tullis Onstott of Princeton University. This water is "an abiotic fringe zone – a place where life could exist but doesn't yet", he says. "This is a zone that's been trapped for billions of years, providing a geological experiment on the genesis of life."
At most, the Timmins and Sudbury water is 2.7 billion years old – the age of the rock it is trapped inside. That's about a billion years after life got started, so the researchers are not suggesting they have bottled the actual primordial soup in which life began. But the chemistry they are seeing corresponds to water that could have given rise to life.
"Geochemically, it's the kind of site that has been invoked for the origins of life on our planet," says Onstott. "Yet here we see it isolated from the present-day DNA world."
There are two leading theories for where life got started on Earth. Perhaps the most famous is Darwin's "warm little pond" – a soup of organic chemicals bathed in sunlight. The other, which has gained popularity in recent years, is that deep-sea vents at the bottom of the ocean acted as a cradle for life, offering both heat and nutrition via fluids pumped up through Earth's crust.
That's where the ancient water from the Ontario mines comes in. The rocks they are held in were formed by hydrothermal vent systems at the bottom of the ocean, billions of years ago.
"I would say this is as close as we have come to bottling the warm little pond, in a warm little fracture," says Sherwood Lollar. Onstott agrees: "They are literally like Darwin's warm little pond without the light."
Having bottled Earth's primordial soup, the researchers are now probing it to see what they can learn. It may be that chemical reactions deep underground have given rise to some of the very earliest stages in the formation of life, like the generation of amino acids, or the building blocks of DNA.
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