BOZEMAN -- Twenty-five years ago, the late astrophysicist Thomas Gold predicted that scientists would find microorganisms living in extreme heat in the hard rocks of Earth's crust.
A Montana State University team and their collaborators who have found such microorganisms in subsurface environments located in Montana, Colorado and the Middle East country of Oman, have now published a paper saying Gold was right about some things and mistaken about others. Either way, Gold set the course for a new field of research that has plenty of room for more explorers.
"It's an exciting time. It's a frontier as unique and potentially as fruitful as when people were first exploring Antarctica," said Eric Boyd, assistant professor in the Department of Microbiology and Immunology in MSU’s College of Agriculture and College of Letters and Science.
Boyd, along with MSU postdoctoral researcher Dan Colman and their collaborators, published a retrospective paper on July 3 in the Proceedings of the National Academy of Sciences about the accuracy and significance of Gold's controversial predictions. PNAS is the official scientific journal of the National Academy of Sciences and covers biological, physical and social sciences. Gold published his predictions in the same journal in the same month a quarter-century ago.
Among other things, Gold speculated that scientists would discover a "deep, hot biosphere" in Earth's crust. This life would extend down for several miles until it became too hot to support life.
He was right about that, Boyd said.
MSU alone has found bacterial microbes living in the cracks of 2.7-billion-year-old rocks in the Beartooth Mountains of Montana; 360-million-year-old rocks in the Henderson Mine in Colorado; and 100-million-year-old rocks in Oman. Boyd said the microbes thrive in these environments and could be found in rocks with temperatures as high as 251.6 degrees Fahrenheit or possibly even higher. He said these microorganisms can be considered “highly efficient miners” that get their energy from extracting chemical energy from minerals instead of using light as a source of energy. They live off the hydrogen, methane and other forms of energy produced by chemical reactions between rocks and water.
Gold predicted, too, that microbes living in the hot rocks of the crust would be able to live off of hydrocarbons such as oils that could be replenished from Earth’s mantle with no biological processes involved. He was wrong on that point, Boyd said, which means, among other things, that oil supplies cannot be replenished from non-biological processes that take place in the mantle.
"I would say we have learned a whole heck of a lot since Gold made his postulations 25 years ago, but we still know so very little about these ecosystems," Boyd said.
Colman said the discoveries they have made about microbial life that exists under extreme conditions provide a better understanding of life on this planet. Their findings may also help in the search for life on other planets, in particular, rocky planets like Mars.
"You are not going to go to Mars and look for trees,” Boyd said. “You are going to look for the most simple forms of life, such as microbes that live off of minerals, that set the stage for higher forms of life. If you find those simple forms of life, you will be compelled to look for more complex forms of life."
Noting that it's expensive to drill down to rock that might house heat-loving microbes, Boyd said it's also difficult to obtain funding for this type of research. For those reasons, the scientists hope to work more closely with exploration mining companies and other enterprises that already drill into the hard rocks of Earth's crust.
MSU researchers are involved in drilling operations in Oman, Boyd said, because they can easily access the layer below the crust there, allowing them to expand their search for life down and into the mantle. They also continue to explore the hot springs of Yellowstone National Park because the pools bring extremophiles, as heat-loving microorganisms are called, to Earth's surface making them easy to study.
Colman, lead author of the PNAS paper, earned his doctorate at the University of New Mexico and joined Boyd's laboratory two years ago. He is the grandson of the late Kenneth Colman, former manager of the MSU Wool Lab. Co-authors in addition to Boyd were Saroj Poudel at MSU and Blake Stamps and John Spear from the Colorado School of Mines, under the auspices of the NASA Astrobiology Institute at Mountain View, California.
Boyd noted that he, Colman and Spear each specialize in a different area of microbiology, so this was the perfect group and time to write a retrospective paper on "The deep, hot biosphere: Twenty-five years of retrospection."
"What this paper does is really serve as a road map for where we feel that the field should go and where the highest return might be," Boyd said.
He added that, "It's a fun time to be doing this kind of work. Literally, the field is wide open. Even if you flooded the field with investigators, the sandbox could never be too small."
The PNAS paper grew out of a partnership between MSU's NASA Astrobiology Institute and the National Science Foundation. The NSF's International Continental Scientific Drilling Program, the NAI, and other groups provided funding for drilling work that is taking place in Oman.
Gold was an Austrian-born astrophysicist who worked at Cornell University. He died in 2004. Although he did not have a doctorate, the MSU team said he was a highly recognized scientist who often contributed his thoughts to fields well beyond astrophysics.
Eric Boyd, email@example.com or (406) 994-7046