Decades of drilling into Earth’s crust has revealed a vast and poorly explored habitat for microbes. Some scientists are trying to fill in the gaps by combining existing sampling data with what we know about subsurface habitats.
Robert Pockalny (University of Rhode Island, USA), Sabin Zahirovic, Xiaodong Qin (both at University of Sydney, Australia), and Rick Colwell (Oregon State University, USA), along with members of the EarthByte group and the DCO Engagement Team, compiled and mapped existing sampling sites onto a virtual model of Earth to create a 3D, interactive globe of deep life. The 3D globe can be accessed on any web browser, and clicking on a site brings up additional information including the depth, age, and environment where the samples were collected, as well as the scientific publication that contains the data set.
“I want this to be a tool for researchers to see where we have data and to find areas that are comparable – and then also to identify where we need to get more data,” said Pockalny.
The current map includes data from ocean sediments and the basement rock beneath continents and oceans. The researchers also used predicted temperatures at different depths, based on geophysical models, to identify where they would likely find groups of microbes adapted to specific temperature ranges, from cold-loving psychrophiles at 20 degrees Celsius to the most heat-tolerant hyperthermophiles at 122 degrees Celsius. Pockalny plans to update the map as more sampling data become available.
Currently, Pockalny and colleagues at the University of Rhode Island, Woods Hole Oceanographic Institution, Bigelow Laboratory for Ocean Science, and Texas A&M University are using the map to make better estimates of where and how many microbes live in subsurface environments. Previously, scientists have shown that microbes live in biofilms and as free-living organisms within veins and open spaces inside rocks in ocean crust. Also, the available space decreases with age and depth of the rocks as they become less porous and less permeable. By combining what we know about the temperature of the subseafloor at different depths, the habitat size inside rocks, and how many microbes can live within these spaces, the team can calculate the total number of cells in the ocean crust.
The researchers hope that the map will be valuable for planning – and funding – future deep life research. “I think it would be a really useful tool to include in proposals to say, this is where we have data, this is where the big holes are, and this is why we need to fill those holes,” said Pockalny.