Yellowstone hot spring

Hot springs, such as those in Yellowstone National Park, host microbial communities supported by mineral forms of energy. As such, they provide a readily accessible portal for studying the processes that give rise to nutrients that support microbial life in the deep, hot biosphere.

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Twenty-five years ago, the late astrophysicist Thomas Gold predicted scientists would find microorganisms in the extreme heat and hard rocks of Earth’s crust.

A Montana State University team and its collaborators who have found such microorganisms in Montana, Colorado and the Middle East, have now published a look back at Gold’s prediction, at what he got right and what he got wrong about a field of research that still 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.

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 Gold’s controversial predictions.

PNAS is the official scientific journal of the National Academy of Sciences and covers biological, physical and social sciences. The Austrian-born Gold, who worked at Cornell University, published his predictions in the same journal in the same month a quarter-century ago. He died in 2004.

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 has found bacterial microbes living in the cracks of 2.7-billion-year-old rocks in the Beartooth Mountains; 360-million-year-old rocks in the Henderson Mine in Colorado; and 100-million-year-old rocks in the country of Oman.

Boyd said the microbes thrive in these environments and could be found in rocks with temperatures at least as high as 250 degrees Fahrenheit. He said these microorganisms are “highly efficient miners” that extract chemical energy from minerals instead of light, living off the hydrogen, and methane produced by chemical reactions between rocks and water.

Gold also predicted 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, Boyd said, which means, among other things, that oil supplies cannot be replenished.

“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 microbes living in extreme conditions provide a better understanding of life on Earth, and 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 because the pools bring heat-loving microorganisms 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. Co-authors were Boyd, Saroj Poudel at MSU, and Blake Stamps and John Spear at the Colorado School of Mines.

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.

“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.”

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