Fiction writers have fantasized about it. Prominent scientists have theorized about it. Experimentalists have delved into it. Skeptics have ridiculed it.

But for decades, nobody has had substantial evidence one way or another on the question of whether the depths of the rocky earth harbor anything that could be considered part of the spectacle of life - until now.Two teams of scientists, drilling deep beneath land and sea, have independently come up with tantalizing clues that swarms of microbial life thrive deep within the planet, the evidence in one case coming from a depth of nearly two miles.

Like a lost world, these communities of microbes have been cut off from all other life on the planet for millions of years, in some cases since the age of dinosaurs or earlier.

"We're finding lots of organisms down there," said David R. Boone, an environmental microbiologist at the Oregon Graduate Institute in Portland who is a member of one of the teams.

The microbes brought to the surface are sometimes unique, including the first bacillus ever discovered that is a strict anaerobe, meaning it can live and grow only where there is no oxygen. Its proposed name is Bacillus infernus, bacillus from hell.

The findings are seen as lending support to the theory, once disparaged but rapidly gaining credibility, that the earth has a hidden biosphere of ancient life extending down many miles, whose total mass may rival or exceed that of all surface life.

"It's a very hot topic," Henry L. Ehrlich, a biologist at the Rensselaer Polytechnic Institute and editor of The Geomicrobiology Journal, said in an interview. "The fact that organisms can be found at this extreme depth is a surprise. From the study of soils, it had generally been assumed that below very shallow depths, microbes weren't likely to be found.

"The thinking now is that these organisms aren't just resting there in a state of suspended animation but, when the right conditions prevail, they metabolize and grow."

John A. Baross, a biologist at the University of Washington in Seattle who was an early supporter of the deep-biosphere idea, said, "So far, all the evidence supports it. The implications are that it's an extensive environment."

The repercussions of the discoveries are not just academic. One of the drilling programs, run by the federal Department of Energy, has isolated more than 5,000 microbes from the deep earth and is making them available to scientists in government and industry.

Interested parties include the National Cancer Institute, Pfizer, Du Pont, Monsanto, Hoffman LaRoche, Glaxo, Zymogenetics, Genencor and a half dozen other companies.

"There's a lot of interest," said Frank J. Wobber, head of the subsurface science program at the Energy Department in Washington.

Thriving under high heats and pressures, the microbes are seen as harboring a treasure trove of rare genes and biochemical processes that may yield innovative medical and biochemical tools. Some of the microbes are already being scanned for antibiotics and agents that might help fight diseases like cancer and AIDS.

Asked if the deep drilling might open a Pandora's box of new human ills, the discoverers generally said the subterranean microbes were adapted to an environment so hostile and alien as to greatly reduce the odds of human infection.

"It's doubtful that an organism from a strange environment separated from man would be pathogenic," said Boone of the Oregon Graduate Institute. "The best place to incubate a virulently pathogenic organism is where you have people. There's no reason to fear deep contamination."

Tullis C. Onstott, a geologist from Princeton University who is a member of the Energy Department team, noted that "every day, the earth is uplifted" as its deep parts are brought naturally to the surface by geological forces, and their microbes are "thrown back into the pool."

Until relatively recently, ideas and evidence of deep life were considered either heretical or impossible to defend. The main problem was the risk of contamination from surface microbes.

No matter how detailed the precautions, deep drillers looking for microbial evidence had a hard time convincing their peers of positive results.

But a mix of old and new techniques is changing all that, including the sterilization of drilling rigs and coring tools and the use of physical and chemical tracers to monitor the flow of fluids in the drilling circulation systems, lowering the risk that surface contamination could be mistaken for deep life.

The new drilling methods, said Ehrlich of Rensselaer, "are very careful."

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One team's report on new evidence of deep life is in the current issue of the British scientific journal Nature. R. John Parkes and eight colleagues at the University of Bristol in England, the University of Wales and the Dunstaffnage Marine Laboratory in Scotland analyzed drillings from the Pacific Ocean floor down to depths of 1,700 feet. The deepest samples came from the Sea of Japan.

Rocky cores extracted from sedimentary formations deep under the ocean in the 1980s and 1990s were prepared for analysis with sterilized gear in an atmosphere of sterile, oxygen-free nitrogen. Samples from inside these cores were then examined with high-powered microscopes and cultured, revealing a riot of microbial life.

"Their presence considerably extends the biosphere," the authors said in their report in Nature. The fact that life continued almost unabated as drills bit ever deeper, they said, implied that the biosphere extended much farther down than the drills have reached. "It is likely that bacterial populations are present to much greater depths," they said.

A deeper and broader program of drilling has been conducted quietly in the United States since the mid-1980s by the Energy Department, which forged the nation's nuclear arsenal during the Cold War and, as a byproduct, created an environmental mess whose cleanup is expected to cost hundreds of billions of dollars.

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