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Buried microbes coax energy from rock

Here’s yet another reason to marvel at microbes: Buried deep within Earth at temperatures and pressures that would kill most living beings, bacteria and other tiny organisms not only survive but apparently even coax the rocks around them to produce food.

Researchers have found that the mere presence of microbes triggers minerals to release hydrogen gas, which the organisms then munch. “It looks like the bacteria themselves have an integral role in liberating this energy,” says R. John Parkes, a geomicrobiologist at Cardiff University in Wales.

His team’s findings appear in the March issue of Geology.

The work helps explain how microbes can survive up to kilometers deep in a subterranean world far from any sunlight to fuel photosynthesis. Such “deep biospheres” may even exist on other planets, Parkes says, with organisms tucked safely away from frigid temperatures and lethal radiation at the surface.

On Earth, some two-thirds of all bacteria, along with another group of single-celled organisms known as archaea, are thought to lurk underground. Scientists have long wondered where these critters get their energy.

Earlier work showed that the microbes fed, in part, on decayed organic matter that settled to the seafloor and formed thick sediments there — a sort of microbial smorgasbord. Parkes and his colleagues decided to look instead at inorganic minerals that can wash offshore and also end up in those sediments.

The researchers ground up a variety of minerals, such as quartz, and put them in a sludgy sediment. In some mixtures they added a dash of microbes to start things off. The scientists then heated the mixtures to various temperatures up to 100 degrees Celsius — what might be found 3 to 4 kilometers deep — and waited to see what happened over several months.
 
 

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