May 31, 2013
Water-Rock Reaction Could Provide Energy For Martian Microbes
Brett Smith for redOrbit.com - Your Universe Online
Previous research has shown how rock-water reactions can produce hydrogen when temperatures are far too hot for living things to survive, such as near hydrothermal vent systems on the ocean floor. However, a new study in Nature Geoscience reports that the same hydrogen-producing reaction can also occur at more hospitable temperatures.
"Water-rock reactions that produce hydrogen gas are thought to have been one of the earliest sources of energy for life on Earth," said Lisa Mayhew, who worked on the study as a doctoral student at the University of Colorado, Boulder.
"However, we know very little about the possibility that hydrogen will be produced from these reactions when the temperatures are low enough that life can survive,” she added. “If these reactions could make enough hydrogen at these low temperatures, then microorganisms might be able to live in the rocks where this reaction occurs, which could potentially be a huge subsurface microbial habitat for hydrogen-utilizing life."
When water infiltrates iron-rich igneous rocks, a few unstable atoms of iron can be released into the water. These unstable atoms, known as reduced iron atoms, can split water molecules to produce hydrogen gas and new minerals containing a more stable, oxidized form of iron at temperatures above 392 degrees Fahrenheit.
To see if these reactions are possible, the researchers submerged rocks in oxygen-free water at temperatures between 122 and 212 degrees Fahrenheit. They were able to detect some evidence of a hydrogen-creating water-rock reaction — possibly enough hydrogen to support life.
Next, the researchers accelerated electrons in a small storage ring to create "synchrotron radiation" that would allow them to establish the type and location of iron in the rocks on a microscopic scale.
Instead of seeing the reduced iron in the rocks converted to the more stable oxidized state, as they are at higher temperatures, the scientists discovered newly formed oxidized iron on minerals with a cubic structure called ℠spinels´ that are highly conductive.
The researchers theorized that the conductive spinels were facilitating the swap of electrons between reduced iron and water, a necessity for the iron to divide the water molecules and create hydrogen gas.
"After observing the formation of oxidized iron on spinels, we realized there was a strong correlation between the amount of hydrogen produced and the volume percent of spinel phases in the reaction materials," Mayhew said. "Generally, the more spinels, the more hydrogen."
The researchers said hydrogen gases produced in these rocks would potentially be able to feed microbial life in a large volume of rock on Earth. They added that low temperature reactions could also be occurring in the same types of rocks that also are prevalent on Mars. Because the minerals that form as a result of these reactions have been found on both Earth and Mars, the new study´s findings may have implications for investigating potential Martian microbial habitats.
NASA announced recently that its Curiosity rover recently spotted preliminary evidence of an ancient streambed on Mars. “¯The study´s results suggest that hydrogen-dependent life could have existed where the Martian streambed was in contact with iron-rich igneous rocks.