Study uncorks possibility that ancient water supports ancient life
Water gushing from a deep mine in Ontario has been isolated from the surface for more than a billion years, a Canadian-United Kingdom scientific group reported today. Intriguingly, the water contains hydrogen and methane, which support bacteria and bigger organisms in the ocean depths, another location where sunlight, life’s usual source of energy, is unknown.
Several analyses indicate that the mine water has been underground for 1.5 to 2.5 billion years, more or less.
Tests for bacteria in the Ontario samples are not complete, but scientists have already found microbes trapped for millions of years in a South African gold mine.
The new study could expand the size and age of the immense bacterial realm beneath our feet, and could even help justify the search for life inside Mars, where geologically quiet regions may retain the liquid water that dominated the planet’s surface billions of years ago.
In deducing how long the water has been isolated from the surface, the researchers focused on inert gases like helium, xenon and argon, which abstain from chemical reactions.
The isotopes of an element are chemically identical but have different physical properties, such as mass. Particular isotopes can only come from a limited number of sources, and do not undergo radioactive decay.
The ultimate source of helium-4 is uranium, and measuring helium-4 can produce an age for the fluid, says project leader Chris Ballentine of the University of Manchester. “We know the concentration of uranium in these rocks, and can calculate that it would take X number of years for this level of helium-4 to build up.”
The researchers calculated that the accumulation of helium-4 would require about 1.14 billion years. Argon-40, another stable isotope, derived from potassium, would require 1.5 billion years. Those dates could be off by hundreds of millions of years in either direction.
Three xenon isotopes provided data on isolation from the surface. “Other workers have been looking at how the xenon isotope composition in the atmosphere has evolved,” says Ballentine. “A small amount of the atmosphere is dissolved in water when it is last at the surface, and when the water percolates into the ground, it takes that signature with it.”
The final step is to match the xenon concentration in the underground water to a time when the same concentration was present in the atmosphere; this process yielded an age of about 1.5 billion years.
Answering the “so-what?” question
The study gives a new view of how water behaves deep underground, says Ballentine, who studies fluid migration. Knowing how fluids form and move will, for example, shed light on what may happen if carbon dioxide gas is pumped underground to reduce greenhouse gas pollution.
Although the ancient water contains methane and hydrogen, which support bacteria in some locations, the “million dollar question” remains to be answered, Ballentine says. Nobody yet knows whether life is present in the water from the Ontario mine. Still, he adds, “We have found an environment that can host life, support it and nurture it for hundreds of millions, or billions of years.”
Because the ancient rock in the Ontario mine is located on the Canadian Shield, where earthquakes and volcanism are absent, “the most important implication is the extent of time that these environments can support life… without being disrupted.”
It’s almost certain that similar locations exist elsewhere, Ballentine adds. “Eventually we hope to find a spectrum of ages that would allow us to … start building a far better understanding of how life finds these pockets, evolves in them, and survives in them.”
Admittedly, that statement is premised on a big “if.” As Ballentine concedes, “We don’t know if there is there life down there, or even what it would look like.”
— David J. Tenenbaum