When first learning about the Sanford Underground Research Facility in Lead, imagine it as a vast, inverted apartment complex. Experiments move into the large, underground caverns. And SURF provides the usual amenities: electricity, running water, elevator maintenance, radon mitigation, liquid nitrogen deliveries and, of course, shielding from cosmic rays.
But amidst the facility’s 370 miles of tunnels, shafts and drifts, there is one group of tenants who pay no rent at all. At SURF, billions of microorganisms — known to biologists as “extremophiles” for their ability to carve out a living far from sunlight and with limited oxygen — live deep underground.
This summer, a research group from South Dakota Mines retrieved a core sample — a smooth cylinder of grey rock — from 4,100 feet below of the surface of SURF. Under a microscope, it wriggled with SURF’s hardiest inhabitants.
From this sample, the research group hopes to find a microbe with a distinct set of characteristics that could help store excess greenhouse gases deep underground.
While extremophiles have slowly evolved to withstand their adverse habitat, scientists are on a mission to keep the Earth’s atmosphere as hospitable as possible. And so, a global effort is underway to store carbon dioxide emissions in deep underground reservoirs. One promising method to keep it locked in place is called “carbon mineralization.”
“Carbon dioxide gas is captured from the atmosphere, then pumped in liquid form deep into underground rock formations,” said Bret Lingwall, a geotechnical, bio-geotechnical and earthquake engineering researcher, who leads the Mines research group. Deep underground, a chemical reaction transforms the CO2 into a stable, solid carbonate mineral — effectively trapping it for millennia.
But this process has a severe limitation: speed.
The crippling pace of the method’s chemical reaction is measured — not in weeks or months — but in years. Currently, the largest carbon mineralization project on Earth can sequester 10,000 tons of CO2 each year — barely a drop in the bucket when climatologists measure carbon emissions by the gigaton (one billion tons).
Meanwhile, Earth is in a bit of a rush.
For carbon mineralization to have an effect, the process desperately needs some added speed.
“What we are trying to do is to accelerate that timescale from a couple of years to a couple of weeks,” Lingwall said. “How we propose to do that is through microbial acceleration.”
Scientists have identified certain microbes that, at the surface, produce enzymes that can greatly accelerate carbon mineralization.
“However, these microbes can’t stand the temperatures, pressures and acidic pH of the deep subsurface,” Lingwall said.
At depths of 4 to 8 kilometers deep, pressures are intense and temperatures climb to 60 to 90 degrees Celsius (140 to 194 degrees Fahrenheit). While these conditions are ideal for carbon storage, they aren’t hospitable to most microbes.
But most microbes weren’t born on the 4100 Level of SURF.
Rajesh Sani, a microbiologist with the Mines research group, has studied various SURF extremophiles for 15 years. In that time, he’s worked with “thermophiles,” a type of extremophile that can survive temperatures from 54 to 70 degrees Celsius (130 to 158 degrees Fahrenheit).
Sani will examine the gene expressions of microbes found in the core sample.
“This process will give us an idea of how these microorganisms function, what are they eating, how they are breathing, how they are producing biomass, and how they are interacting with rock samples underground,” Sani said.
It will also help researchers determine if SURF’s extremophiles can produce the sought-after enzyme that hastens carbon mineralization.