Life in the Inferno: Researchers Identify Factors that Determine Where Microorganisms Can Survive in the Hellish World Deep Underground

Contact: Mary Beckman
beckmt@inel.gov
208-526-0061
Idaho National E & E Laboratory

Life in the inferno: researchers identify factors that determine where microorganisms can survive
in the hellish world deep underground

Life in the Inferno: Researchers Identify Factors that Determine Where Microorganisms Can Survive in the Hellish World Deep Underground

Even Dante would blanch at the conditions kilometers below the earth’s surface. Temperatures climb
past 100 degrees Celsius, pressures hundreds of times greater than atmospheric pressure bear down, and
space is so tight even microorganisms can barely budge.

Yet, even there life persists. Now subsurface scientists have begun to identify the factors that
determine why microorganisms survive deep underground in some places, but not others, report
researchers from the Department of Energy’s Idaho National Engineering and Environmental Laboratory
and Princeton University. The INEEL specializes in subsurface science as part of its environmental
mission.

High temperatures ensure nothing can live too far below the earth’s surface. But pressure, the
availability of water, the porosity of the surrounding rock and the flow of chemical nutrients also
limit where extremophiles–microorganisms that relish harsh conditions–can exist.

As recently as the 1980s most microbiologists thought nothing could survive far below the soil
layer. They now know extremophiles live embedded in rock hundreds of meters below dry land, in deep
ocean sediments and in fissures crisscrossing the ocean floor.

“We’re at the point of recognizing that microorganisms have remarkable abilities to colonize these
environments and trying to understand the parameters that control that colonization,” said INEEL
microbiologist Rick Colwell, who presented a synthesis of recent findings in the Biogeoscience: Deep
Biospheres: Where and How? poster session today at the American Geophysical Society meeting in San
Francisco.

A better understanding of how extremophiles survive deep underground may shed light on how life
endured the earth’s violent youth, or show scientists where to look for life on other planets, said
Princeton geochemist T.C. Onstott.

Temperature appears to be the primary factor in limiting how deep extremophiles can go. No known
microorganism can live for long at 120 degrees Celsius. Since the surface temperature averages 15
degrees Celsius and the temperature in the ground increases with depth about 19 degrees Celsius every
kilometer, extremophiles should die off between five and six kilometers below the surface of dry land.

Near geothermal hotspots, subsurface temperatures rise much more rapidly, and life survives only
near the surface. In deep ocean sediments, where kilometers of cold water above keep temperatures
down, extremophiles may thrive at depths of several kilometers below the ocean floor.

Pressure limits the range of extremophiles less than temperature does. Most microorganisms can
survive pressure 600 times atmospheric pressure, which corresponds to a depth of six kilometers. At
that depth in most locations the temperature likely exceeds 120 degrees Celsius.

Lack of water and chemical nutrients likely prohibits deep subsurface life in arid, geologically
stable regions. For instance, little grows between the surface and the groundwater of the Snake River
Plain, on which INEEL sits.

Conversely, extremophiles may be more abundant deep in active geological features, such as faults,
mid-ocean ridges and salt deposits, where fluids and nutrients flow more freely.

Subsurface environments are so austere some extremophiles live in a state of nearly suspended
animation. Microorganisms living on the surface divide after hours or days. Those living deep
underground may divide only after hundreds of thousands of years.

Life may have persevered below the surface 4 billion years ago, when asteroids routinely pelted
the earth and caused the oceans to boil, Onstott said, so microorganisms living deep underground may
provide clues about the emergence of life on the developing planet. “If you want to understand
primitive microbial ecosystems, the only place you can go is into the subsurface,” he said.

If life exists elsewhere in the solar system, it may be tucked beneath the surface of other
planets or their moons. By studying subsurface extremophiles on earth, researchers may learn where to
look in their search for extraterrestrial life.

As data accumulate, researchers hope to understand the processes that control life deep below the
surface well enough to predict what they will find in a given locale. “In the early days it was
discovery-driven science–let’s drill a hole and see what we find,” Colwell said. “I think it’s now
moving into what I’d call hypothesis-driven science.”

Onstott agrees. “In terms of microbiology,” he said, “I think the field is headed toward
identifying energy sources for these microorganisms, correlating these sources to microbial activity
and determining whether that activity has changed the subsurface environment.”

The INEEL is managed and operated by Bechtel BWXT, Idaho, LLC (BBWI) for the U.S. Department of
Energy.

Media contacts:
Adrian Cho, 208-526-3176,
choha@inel.gov,
Mary Beckman, 208-526-0061,
beckmt@inel.gov

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