No. 85: Jan-Feb 1993
It is accepted that every cubic centimeter of the topsoil beneath our feet seethes with thousands of microorganisms. It is less well known that life's domain extends down much further. The hard rocks and strata of earth's crust -- seemingly sterile and inert -- are continuously being transformed by bacteria and other life forms. In fact, it was easy to find three examples of such processes from the literature collected from the past two months.
Although the discoveries reported below may seem dull to anomalists ued to more exciting fare, it may well be that life from "inner space" has been and will be more important to humankind than life from "outer space," as implied in third item!
Bacteria and placer gold.
"Lacelike networks of micrometresize filiform gold associated with Alaskan placer gold particles are interpreted as low-temperature pseudomorphs of a Pedomicrobium-like budding bacterium. Submicron reproductive structures (hyphae) and other morphological features similar to those of Pedomicrobium occur as three-dimensional facsimiles in highpurity gold in and on placer gold particles from Lillian Creek, Alaska."
In short, bacteria help create placer gold deposits. The author believes that bacterioform gold is widespread. (Watterson, John R.; "Preliminary Evidence for the Involvement of Budding Bacteria in the Origin of Alaskan Placer Gold," Geology, 20:315, 1992.)
Microorganisms and iron deposits. At least 500 million years ago, filamentous bacteria and/or fungi were already playing vital roles in the deposition of iron from hydrothermal fluids. Abundant microbial filaments indicative of biological activity are found in the Cambrian ironstones in Australia's Thalanga deposit. (Duhig, Nathan C., et al; "Microbial Involvement in the Formation of Cambrian Sea-Floor Silica-Iron Oxide Deposits," Geology, 20:511, 1992.)
Deeper implications. The formation of placer gold and ironstone are only part of the repertoire of deep-living microorganisms. A five-year survey of microbial life conducted by the U.S. Department of Energy (DOE) found that bacteria were everywhere -- even 3 kilo meters deep in a Virginia borehole. F. Wobber, the DOE manager of the project underscored the mystery and probable importance of "biogeology":
"Besides asking how subsurface bacteria affect geology, he wonders how geologic processes could have carried living things so deep into the planet. 'When you find these organisms at great depths,' he says, 'you have to ask: Where did they come from?' Microbes from the soil could easily infiltrate shallow aquifers...but in very deep sediments, like those in the Texaco well, the microbes may have been entombed when the rock was first deposited, tens or hundreds of millions of years ago. If so, the deep Earth might be a den of survivors, toughened by millenia of evolution in their harsh environment. Attacking rock might be just one of their feats.(Appenzeller, Tim; "Deep-Living Microbes Mount a Relentless Attack on Rock," Science, 258:222. 1992.)
Comment. Is Wobber suggesting that these super-tough, deep-living bacteria might be dangerous to humans, like the microorganism from outer space in the movie The Andromeda Strain?
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