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.

Loading... Loading... Loading... Loading... Loading... Loading...

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.”