SCIENCE : Yellowstone Geysers Spew Fossil Clues to Primeval Life : Intricate mineral tufts and terraces may help decode relics of microscopic life on Mars.

Kneeling at the edge of a splashing hot spring, Jack Farmer gingerly taps his chisel against a thin mineral tuft rising from the pool’s brim. After snapping off a pea-sized chunk of stone, he holds it up for inspection.

Red and green bands stripe the tiny piece of rock as if it were a miniature slice of layer cake.

“Those are bacteria, living cells,” says the National Aeronautics and Space Administration research scientist. “As they get coated with minerals, they are encased and fossilized right before our eyes.”

Where tourists see intricate mineral tufts and terraces adorning Yellowstone National Park’s hot springs and geysers, Farmer sees crusty catalogues of past life. In the pale yellow and gray formations, he seeks clues that may lead him to similar, telltale relics of microscopic life on Mars.

Steaming thermal basins like Yellowstone’s may be rare today but were commonplace during Earth’s early days. So common, in fact, many scientists suspect hot springs were the original incubators of life, which for most of its history on Earth took the form of simple one-celled microbes.

Millions of microbes still flourish in Yellowstone’s simmering waters, some as feathery filaments waving in the current, others as thick mats that look like green, growing JELL-O.

The primitive organisms closely resemble the earliest life on Earth. And they may not be so different from the first life that would have appeared on other planets.

Just like Earth, the modern Martian landscape is far different from what it once was. Although it’s now barren, river channels and lake beds visible from spacecraft attest that water was abundant 3.5 billion years ago, about the same time life developed on Earth.

Altered by the same kind of volcanic forces that heat Yellowstone, Mars is home to the largest volcano in the solar system, a peak three times higher than Mt. Everest. Fueled by such fiery heat and water, hot springs probably once gurgled on Mars--offering life another foothold in the solar system.

Since bacterial life appeared early in Earth’s 4-billion-year history, Farmer figures it might have developed on Mars too. If it did, the tiny creatures may have left fossil footprints in hot spring mineral deposits, just as microbes in Yellowstone do today.

It is those tracks that Farmer would like to find.

Any primeval life on Mars might have vanished as the planet’s atmosphere dissipated over later eons, taking liquid water with it. Or, Farmer says, Martian microbes may have since become subterranean dwellers--moving underground, closer to the heat source of the planet’s center.

But in a convergence of biology, chemistry and geology, hot springs entomb their tiny inhabitants in calcite, silica and iron that builds up--like residue on a bathroom faucet--where water bubbles to the surface. So any organisms in Martian springs should have left a Stone Age diary behind.

“We want to know what information gets incorporated into the rock and then how you get that information out,” says Farmer, poking at crunchy shoots of bacteria that have just begun to accumulate a mineral crust. Once laminated with rock, they may last billions of years.

To pinpoint similar remains of Martian hot springs, Farmer and his colleagues are first taking what lessons they can from Earth. By comparing high-altitude photographs of regions like Yellowstone to what they find on the ground, they hope to single out distinctive topographic impressions of ancient hot spring terraces.

“Once we can recognize these environments on Earth, we should be able to recognize them on Mars too,” adds Farmer, who is based at NASA’s Ames Research Center in Northern California, where he works at the Search for Extraterrestrial Intelligence Institute.

Two spacecraft are scheduled to lift off for Mars in 1996, succeeding the failed Mars Observer mission. One will survey Martian terrain from above, while the other--the Mars Pathfinder--will land. With Farmer’s input, NASA expects to direct the lander to a broad river plain that may hold fragments of eroded hot spring terraces.

The space agency then plans to launch another Mars orbiter and lander roughly every two years.

“Everybody wants to ask that question, ‘Can life exist somewhere else?’ ” Farmer says, depositing his small chunk of rock into a vial about the size of his little finger. “Mars not only had a favorable environment for life, but it also had an environment that could have preserved evidence of life.”

In addition to Yellowstone, Farmer and his colleagues have examined California’s Mono Lake, where they will return next summer to probe the lake floor; salt ponds in Baja California, and dry lakes throughout the West.