Scientists still have much to learn about how water and other fluids flow thousands of feet beneath Earth's surface and how this influences microbial life below. Perhaps surprisingly, we know more about the surface of Mars than we do about water and life in the depths of our own planet.

The National Science Foundation Frontier Research in Earth Sciences, or FRES, program awarded a University of Arizona-led team $2.8 million to study how subsurface fluids, rocks and microbes interact and evolve over time. The project has been dubbed SMRFS, short for Subsurface Microbe-Rock-Fluid Systems, which was meant to evoke images of little blue Smurf miners.

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Jennifer McIntosh, a professor in the UArizona Department of Hydrology and Atmospheric Sciences, is the lead principal investigator of the project. Pete Reiners, a professor in the Department of Geosciences, is a co-principal investigator.

The team hopes to learn how changes to the Earth's surface over its history affected the underground biosphere, what geologic and climate factors favor or limit the potential for subsurface microbial life, and what the rock record says about the history of microbial life and its relationship with fluids and fluid-rock reactions.

Addressing these fundamental questions will be no easy feat. There are very few studies about microorganisms deep underground, and the studies that have been done rarely consider the context of microbial life, such as the rocks in which the microbes live and the water by which they're transported, McIntosh said. Earth's subsurface contains most microbial life on Earth – about 90% of bacteria and single-celled microorganisms called archaea and 10%- 20% of all biomass on land.

"The subsurface is like a black box," McIntosh said. To peer into it, the team will partner with oil and gas and mining companies that drill up to thousands of feet deep.

"Like straws or wells, we'll collect the fluids and rock material brought up when they drill as well as any microbes hitching a ride," McIntosh said. The team will also collect samples from various state geological surveys' libraries of rock material and from a few locations where deep fluids come up to the surface naturally, such as hot springs and naturally-flowing wells.

McIntosh, who also holds the title of University Distinguished Scholar, said she's most excited to see where and how life exists beneath Earth's surface.

"This will be the first time that we're collecting and measuring microbial samples all the way from the surface to groundwater to these very deep fluids coming up in oil and gas and mining wells in the same location," she said.

In general, microbial life is limited by temperature, saltiness, pressure and the availability of an energy source, but it can survive in conditions that humans would consider extreme.

"Microbes have been found in million- to billion-year-old, salty waters thousands of feet beneath the surface," McIntosh said. "So, yes, microbes can live in the most extreme environments, including places that you would think would be inhospitable."

McIntosh and her team also want to understand how life existed deep underground tens of millions of years ago.  

"We're going to look for signatures that the microbes and fluids left in the rocks. Then, we will date the rocks to build a timeline of microbial activity and fluid flow. Based on which microbes were active at a specific time, we can potentially say something about the fluids that were circulating through those rocks and how those fluids may have stimulated microbial activity," McIntosh said. "We're also going to determine past temperatures of subsurface environments to identify locations that may have been too hot for microbes to survive."

The team will focus the study on the Paradox and Rio Grande Rift basins in the southwestern United States and, ultimately, create a guide for looking for life in the subsurface throughout geological time.

"We want to make a predictive model for the past," McIntosh said. "At the end, we're hoping to say, 'In this subsurface location, at this time, we would expect life could have survived.'"

The team aims to identify "hot moments" and "hot spots" – specific time periods and locations in the geologic past – within the Earth's crust where subsurface conditions promoted microbial activity. In addition, the project will provide information for effective management and storage of resources from groundwater to energy fuels and waste products.

Other team members include Magdalena Osburn from Northwestern University and Randolph Williams from the University of Wisconsin-Madison, as well as Henrik Drake from Linnaeus University in Sweden and Grant Ferguson from the University of Saskatchewan in Canada. Ferguson is also an adjunct faculty member in the UArizona Department of Hydrology and Atmospheric Sciences.

"Exploration is at the heart of most everything we do at the University of Arizona, and that is no better illustrated than by our exploration of the planet we live on," said University of Arizona President Robert C. Robbins. "As a land-grant university, we have a commitment to deepen our understanding of the past, present and future of life on Earth and then share that knowledge with the wider community. By studying the Earth's subsurface in such detail, Dr. McIntosh and her team are not only pushing the boundaries of what we know about the subsurface, but also inspiring the next generation to continue exploring its mysterious depths."

The project will also involve: training several graduate students; working to recruit and retain first-generation, low-income, community college and underrepresented minority undergraduate students; developing Earth science curriculum for elementary school students; and sharing research results with the public through educational videos. The team will also develop video vignettes featuring research results to engage underserved schoolchildren and the public through the University of Arizona Flandrau Science Center's Earth Science Discovery program.