Sunday, December 21, 2014
Possibility of widespread ‘deep-Earth life’
jolts scientists
What if Earth
hosts another ‘biosphere’ of tiny microbial organisms deep below the surface?
When we think of life on Earth, we usually
picture blue oceans, green forests and the big animals that live in both.
But what if Earth hosts another “biosphere”
of tiny microbial organisms deep below the surface? And what if
extraterrestrial life looks more like this deep, dark world than the sunny
blue-green one we are familiar with?
In a study published Wednesday in the journal
Nature, research led by University of Toronto geoscientist Barbara Sherwood
Lollar demonstrates that the environment that could host “deep-Earth life” is
far vaster than previously imagined.
And the possibility that we could find the
same thing on other planets received an electric jolt Tuesday with the
announcement that NASA’s Mars Curiosity rover had detected a plume of methane on
the red planet that spiked and then dissipated — a potential signal of
microbial life.
“It’s a critical reminder that the oceans and
rivers and lakes on Earth give us a skewed view of the places where life could
exist and evolve in another setting or another planet,” said Lisa Pratt, a
geochemist at Indiana University who was not involved in either paper. Pratt
chairs the Mars Exploration Program Analysis Group, a community of scientists
that advises NASA.
Both papers, Pratt says, suggest that “we
better start looking for something that’s different than the common, ordinary,
cellular life we’re used to seeing and studying on Earth.”
Sherwood Lollar’s announcement follows on two
tantalizing pieces of research published in recent years.
In 2006, she and Pratt were among the
co-authors of a Science paper that announced the discovery of bacteria living
deep in a South African gold mine, completely isolated from sunlight — the fuel
source for all of life on the surface of Earth. These microbes likely derived
their energy from hydrogen gas produced by reactions between water and the
surrounding rock — and they were estimated to have survived down there for
between 3 million and 25 million years.
Then, last year, Sherwood Lollar was part of
a team that described a similar environment. In a mine in Timmins, Ont., the
scientists analyzed water in a deep fracture with similar chemistry to the
South African mine. The water in the Timmins mine was billions of years old.
The team is still analyzing that site for the existence of microbial life.
So Sherwood Lollar was curious. “How many
places in the planet might we find more?”
By combing through the literature and
visiting sites around the world, she and her Nature co-authors found dozens
more ancient rock sites with similar chemistry, doubling previous estimates of
the amount of energy available to deep life from water-rock reactions.
“Much more of the planet is actually
potentially hospitable for deep life than we thought,” said Sherwood Lollar.
“It’s fantastic. I think it’s really, really
exciting stuff,” says Jan Amend, a geochemist at the University of Southern
California who was not involved in the research.
“If somebody told you all of a sudden that
you had twice as much money in the bank as you thought you had, that would put
a smile on your face,” he said. “That analogy works for microbiologists
especially, because a lot of microorganisms use hydrogen as an energy source.”
Sherwood Lollar will present the findings at
the American Geophysical Union meeting currently underway in San Francisco.
That was where NASA scientists on Tuesday announced that the Mars rover had
detected a tenfold spike in methane near the Gale Crater over the course of two
months. Because the gas wouldn’t last long in the Martian atmosphere, something
must have produced it recently and nearby.
The rover scientists acknowledged that one
potential source is subsurface microbial life that releases methane as a waste
product. But it also could have been produced through inorganic chemical
reactions, and Mars has dashed our hopes as a host for life before.
But both papers will certainly spark a
renewed interest in deep subsurface biospheres.
“Essentially what this says is that the
subsurface of our entire planet is likely a feasible place for life to take
hold,” said Sherwood Lollar. “So when we think about how much of our planet is
alive, we are no longer thinking about just a thin veneer on the surface.”
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