Bizarre Life Forms Thrive Beneath Earth's Surface
In the classic tale, A Journey to the Center of the Earth, Jules Verne imagined elaborate worlds in a hollow, miles beneath our feet. More modern science-fiction novelists have dreamed of spheres in outer space where earthling astronauts encounter alien life forms. Now these two ideas are being fused in a bubbling witches' cauldron: deep within the planet may be the best place to find new life forms on our planet--and glean clues to possible life on others.
Vaporous hot pools far beneath Earth's surface support microbes conducting the business of life at extreme temperatures and pressures. The microbes, some of which are bacteria, are all called extremophiles, and their potentially far-reaching domain is called the subsurface biosphere.
Life in Extreme Environments
In mid-March, at a workshop funded by NSF, more than 100 scientists gathered in Washington, D.C., to discuss the subsurface biosphere. At this stage, stated the workshop's organizers, there is little doubt that a subsurface biosphere exists; at issue are its nature and extent. The workshop brought together researchers from fields as varied as geology, chemical oceanography, biological oceanography, microbiology and physics.
Workshop attendees reviewed evidence for subsurface microbial life, considered the physical and geochemical nature of these environments, looked at the diversity of organisms potentially living in the subsurface and their physiological adaptations, and discussed research strategies for sampling and observing the subsurface biosphere.
Plumbing the Depths
Participants noted that extremophiles living closer to the earth's surface have already been studied. These include organisms living in the deep-sea hydrothermal vents and hot pools in Yellowstone National Park.
Furthermore, the molecules that allow these extremophiles to prosper are already intriguing industries. With potential applications ranging from the production of sweeteners and "stonewashed" jeans to the genetic identification of criminals and diagnosis of infectious and genetic diseases, scientists are investigating the "survival kits" of these heat-loving, pressure-tolerating organisms.
But now, tantalizing evidence is taking these scientists--or, more accurately, their instruments--deeper and deeper into the planet.
In A Journey to the Center of the Earth, the zealous Professor Von Hardwigg finds a riddle in Icelandic parchment. This discovery lures him and an intrepid party of explorers on an adventure into the bowels of our planet. Today, in a story no less strange, researchers are following clues leading them on a fantastic descent into Earth's subterranean world, where an entire biosphere of extremophiles ferments in superheated, vise-pressured darkness.
The tale begins with Cornell University theorist Thomas Gold, who led discussions five years ago about how Earth could be harboring a biosphere of deep microbial life that extends for miles. Gold argued that the total mass of this biosphere might rival or exceed that of all surface life. As evidence, Gold talked of the microbes that had been found in deep-sea hydrothermal vents in terrestrial hot springs like those of Yellowstone National Park, and in other deep, hot places. He then suggested that microbial life might be widespread throughout the upper few miles of Earth's crust, inhabiting pores and cracks among rocks and living off Earth's inner heat and bubbling broth of chemicals. Not needing sunlight, this kingdom of microbes could exist independently of Earth's surface.
Gold's theory was soon put to the test by scientists like John Baross and Marv Lilley, both of the University of Washington (UW) at Seattle, and Kim Juniper, of GEOTOP at the Université du Québec at Montreal, Canada, among other researchers. Baross, Lilley and Juniper were co-conveners at the NSF subsurface biosphere workshop.
Expanding Life's Boundaries
In 1993, Baross and UW colleague Jody Deming published a paper entitled "Deep-sea smokers: Windows to a subsurface biosphere?" This paper advanced Gold's theory one more step by theorizing that Earth holds not only thermophilic (heat-loving) organisms, but also "superthermophilic" microbes that live at even more extreme temperatures.
The paper states that superthermophilic microorganisms inhabit pressurized environments beneath deep-sea hydrothermal vents. These super-organisms not only exist, but thrive at temperatures up to and possibly beyond 150o Centigrade (more than 300o Fahrenheit), setting a new limit at which life can exist.
After Baross and Deming published their paper, John Parkes discovered bacteria in a marine sediment core that substantiated the idea of superthermophilic organisms. While working with the NSF-funded Ocean Drilling Project, Parkes, of the United Kingdom's University of Bristol, discovered bacteria that lives at a temperature of 169o Centigrade.
Deming and Baross also offered new geochemical information collected from the Endeavour Segment of the Juan de Fuca Ridge in the deep Pacific Ocean off the U.S. West Coast. These explorations, conducted in the submersible Alvin, indicated that organic materials--the building blocks of life--exist below the surface of hydrothermal vents along the Endeavour Segment.
Deming and Baross added that it is likely that life in the subsurface is a two-way street: microbes living beneath these deep-sea vent--called smokers--change the chemistry of the froth spewing out, just as the microbes themselves depend upon this chemical stew to survive. The smokers got their name because of their chimney-like structures through which fluids from within the planet are released to the surrounding deep ocean.
Connections to Other Worlds
Could there be an entire ecosystem functioning in Earth's subsurface environment?
While this question remains unanswered, today's journey beneath Earth's surface continues, with new questions constantly arising. Says Baross, "Who knows, the subsurface biosphere may be inoculating' the surface biosphere with new seeds of life. And perhaps, if there's a biosphere beneath the surface here, there might also be one under the surfaces of other planets."
To find out, adds geologist John Delaney of UW, scientists first need new ways of collecting samples of this distant, extreme environment on Earth. "We need a system of semi-permanent observatories placed at strategic points along the sea floor that would provide us with new ways of peering beneath the surface."
To help scientists get this kind of information, NSF has created a new funding initiative called "Life in Extreme Environments," or "LexEn." Total funding of $6 million is currently available to scientists exploring the relationships between organisms that live in extreme environments and the extreme environments themselves.
"We believe that the study of extreme environments on Earth and the life they support," says Mike Purdy, coordinator of the new NSF initiative, "is the most effective way of understanding how and where life may exist on other planets and what the limits of life might be on our own."
Research supported by LexEn is expected to lead to the discovery of a diverse group of microorganisms, the lifestyles and biology of which can now only be guessed, Purdy adds.
"We advanced regardless of everything drawn on by ardent curiosity," wrote Jules Verne in A Journey to the Center of the Earth. "What other marvels did this great cavern contain--what other wondrous treasures? My eyes were quite prepared for any number of surprises, my imagination lived in expectation of something new and wonderful."
Scientists like John Baross, Marv Lilley and Kim Juniper would no doubt agree. "If anyone tells me they have a theory on this subject that's even remotely plausible," says Baross, "I have an open mind."