For more than a decade, scientists have known microbes can live under glacial ice sheets that are millions of years old, but the mechanism that allows the light- and organic carbon- starved microbes to obtain energy for survival has been a mystery.
Now, research by Montana State University professors and others appearing in the November issue of Nature Geoscience has found that the grinding action of glaciers and ice sheets against silicate rocks, when combined with water, releases enough hydrogen gas to sustain methanogenic archaea, or microorganisms that produce methane.
Mark Skidmore, associate professor of geology in the MSU College of Letters and Science, and Eric Boyd, assistant professor in the Department of Microbiology and Immunology in the MSU College of Agriculture and MSU College of Letters and Science, co-authored “Rock Comminution as a Source of Hydrogen for Subglacial Ecosystems” with colleagues from the U.K, Norway and Ohio. Nature Geoscience is the number one-ranked multidisciplinary geoscience journal.
“This is the first time that this mechanism has been considered in a glaciated environment, and I would say it’s an important mechanism for supporting life in any subsurface system,” Boyd said. “This mechanism likely extends to numerous other wet environments where seismic activity or other physical processes lead to shearing of silicate minerals.”
As part of the research, Skidmore and Boyd collected a rock sample from Robertson Glacier near Canmore, Alberta, and sent the samples to lead study author Jon Telling of the University of Bristol’s School of Geographical Sciences.
Researchers then crushed the sample – along with subglacial rock samples from Greenland, Norway and Antarctica – in a lab. The samples were ground into progressively smaller pieces to replicate the physical process of an ice sheet moving against bedrock. During the grinding process, surface minerals were sheared and free radicals formed. When researchers added water to the sample, hydrogen gas was produced – enough to support subglacial microbial communities. The amount of hydrogen produced increased with higher temperatures and with increased surface area of the crushed rock.
The hydrogen-generating mechanism is an important process for microbes existing under ice sheets for extended periods of time, Skidmore said. Initially, sub-glacial microbes can obtain organic carbon from soils or vegetation that are overrun as an ice mass forms, but eventually these organic carbon energy sources become depleted. Once they’re exhausted, the availability of hydrogen becomes key to the survival of these microbes. Skidmore said such environments include East Antarctica, which has been covered in ice for millions of years.
Past periods of global glaciation on Earth, such as the Neoproterozoic glaciation of 700 million years ago, are implicated in this finding as well. During Neoproterozoic glaciations, sometimes referred to as the “Snowball Earth” events, most of Earth’s continents were covered in ice.
NASA provided funding for Skidmore and Boyd’s research on Robertson Glacier.
Boyd said that NASA is interested in studying the limits of life on Earth – looking at high and low temperature extremes, for example – to better understand potential for life on other features of our solar system.
“There are silicate rocks on Mars, and also ice caps and glacier-like features, so there’s no reason to believe why ice on Mars grinding up silicate rocks shouldn’t interact with basal melt water to produce hydrogen there, exactly as it does on Earth,” Skidmore said.
Boyd was a post-doctoral fellow with the NASA Astrobiology Institute from 2009 to 2011 and conducted research on Robertson Glacier that focused on methane producing microorganisms in subglacial ecosystems.
Skidmore and Boyd were also awarded a grant from the NASA Exobiology and Evolutionary Biology program to study methane in subglacial sediment at Robertson Glacier. For five years beginning in 2010, they went to Robertson Glacier two to three times per year to conduct research, sometimes staying up to three months at a time.
Future research building upon the findings published in Nature Geoscience will likely focus on how hydrogen dependent primary producers, such as methanogenic archaea, support more complex forms of life underneath glaciers, Boyd said.
“The obvious next step for us is to figure out the extent to which the hydrogen that is produced by silicate mineral shearing is supporting other forms of life in subglacial ecosystems,” Boyd said. “Not only are we supporting more simple forms of microbial life, we’re supporting complex life in the form of eukaryotes.”
Contact: Mark Skidmore, (406) 994-7251 or firstname.lastname@example.org; or Eric Boyd, (406) 994-7046 or email@example.com