"It's entirely possible a significant portion of Earth's biosphere may remain to be discovered. When I started, I didn't expect to find life there. What a thrill. It's all new."

In 2003, Moser, a microbial ecologist at the Desert Research Institute in Las Vegas, went about two miles into the Earth's crust at the Mponeng Mine and neighboring Driefontein Mine in South Africa to collect samples from water trickling from sealed boreholes near earthquake faults.

The single-celled microbes that showed up at first puzzled the scientists.

"Was it real? Was it a contaminant? We never really knew for sure," he said. "We still can't grow the organism in the lab, but we have all of its genes, its entire genetic history and all of its tools for living at the boundary" of where life exists and doesn't in the crust.

When the research was launched in 1997, "many scientists assumed there could not be life this deep," he said. "We had a hard time understanding ourselves why they should be there. What could they possibly be eating, and what could their energy source be?"

With no sunlight to drive the biological processes needed to support life, Moser and his colleagues have theorized that energy that drives life that deep in the crust can be traced to the natural radioactive decay of elements like uranium, thorium and potassium.

"This radiation first splits water into hydrogen and several oxidants, which in turn lead to the production of sulfate. These bacteria then subsist on the hydrogen and sulfate in a manner similar to the way our own bodies use oxygen."

The life of the deep microbes "requires two things, an energy source and way to use that energy. ... On the surface, we know oxygen from photosynthesis drives that process, but in the subsurface .... those electrons end up being donated to geologically produced sulfate," he said.

Moser, who collaborated with colleagues at the Lawrence Berkeley National Laboratory in California and at other universities, identified at least three new divisions, or "phyla," among the microbes.

"It gives us a new way of looking at the planet. How deep can you go and still be in the biosphere we don't know," Moser said.

"We normally think of the biosphere as being mostly limited to the planet's surface. However, if one accepts that life extends deep into the Earth, the ultimate volume of the biosphere is much greater than we ever realized.

"Even though the density of subsurface life may be relatively low, if you add up all those tiny microbial bodies, you get an enormous amount of life that's equal to perhaps greater than the surface biosphere."

Confirmation of the deep microbes suggests life is not limited to the planet's "thin, lighted veneer at the surface, Moser said.

The addition to the biosphere in the subsurface gives hope life exists beneath the surface of other planets where microbes could be shielded from harsh conditions.

"Humanity is interested in life elsewhere in the universe," Moser said. "Look at Mars. It's the only place we know where life could exist is in the subsurface."

Contact reporter Keith Rogers at krogers @reviewjournal.com or 702-383-0308.