Saturday, January 20, 2007

Tech researchers study rock formations

Group recently submitted funding proposal to the National Science Foundation for project

Argen Duncan El Defensor Chieftain Reporter

For underground petroleum reservoirs and life beyond our atmosphere, the research four New Mexico Tech scientists hope to conduct could change the way we search.

Peter Mozley, Department of Earth and Environmental Science associate professor, said the group recently submitted a funding proposal to the National Science Foundation for research on whether bacteria and the stream of slime they produce when they decompose material can create rock formations called elongated concretions.

This type of concretion forms when minerals precipitate (leave their dissolved state) from groundwater and fill in pores in surrounding sediment. In the proposed research, the mineral in question is calcite, which makes up caliche and limestone.

Collaborator Penelope Boston, research associate professor in Earth and Environmental Sciences, said the "suite of processes" where microorganisms interact with the geological environment is a new field.

"I think the bottom line of this kind of work is biology has had more of an impact on the planet than we recognized in the past, and this kind of work is helping further our understanding of the degree to which that's the case," she said.

In previous research, Mozley concluded that elongated concretions developed their long, stretched-out shape because waste from bacteria decomposing a piece of organic matter in groundwater created a plume of water with chemistry different from the surrounding fluid. The changed chemistry encouraged the calcite to precipitate to form the rock.

The new research would follow up on that work by testing a new hypothesis that the altered water chemistry, the bacteria and their protective slime directly cause calcite to precipitate. Then the three components all make up the rock formation.

"But this is something new," Mozley said.

People traditionally think the concretions are inorganic, he said. However, if the theory were true, it would mean bacteria control the creation of the formations.

"So bugs are controlling things even underground," Mozley said.

This applies to the search for extraterrestrial life. The Mars rovers have discovered rust concretions, evidence the planet once had groundwater.

Boston said if the group could create concretions in a lab only by using microorganisms, they could infer the same happened in nature.

"So it's a geological signature of past life," she said.

Another collaborator, Professor of Hydrology Robert Bowman, said the researchers would see if concretions bacteria formed would have different size, shape or chemical composition than formations created inorganically. If they found a difference in characteristics, it might prove biological activity formed rocks with similar features on other planets.

As for the search for oil and natural gas, the calcite "cement" that forms concretions strongly influences how well fluids move through rock and the amount of pores in the rock, Mozley said. Rock must have many pores to hold petroleum or gas, and be very permeable to allow pumping.

If the rock has too much cement, it won't have oil or gas.

"So if our hypothesis is correct, it could be that the distribution of the cement and where it is in the surface is controlled by some original distribution of bacterial colonies," Mozley said.

To predict where oil is, one would need to forecast where calcite is. If the researchers' theory is true, one would need to predict where the microbes are to forecast where calcite is, Mozley said.

Bowman would design and run the experimental system if the group received funding.

"These are basically going to be small sand tanks," he said. "Kind of like an ant farm."

Water with a specific chemical composition would flow through the tanks at a steady rate. Some tanks would contain organic matter, to serve as a point of formation for the concretions, and bacteria; some would have organic material without microbes; and some would hold only inorganic substances.

The researchers would observe which tanks developed concretions and what differences the rocks had if they formed in more than one type of tank.

Professor of Geology Andrew Campbell said the scientists want to use stable carbon isotopes to track whether the bacteria affect the precipitation of calcite. Isotopes are atoms of the same element that have different weights.

The researchers would feed the bacteria in the experiment acetate with labeled carbon isotopes. Then they would see if the calcite that precipitated contained those isotopes.

aduncan@dchieftain.com

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