How Subsurface Ecosystems Shape and Are Shaped by Basalt Reactivity

A team of geochemists, geobiologists, and microbiologists from ISTerre (CNRS/Université Grenoble Alpes), IPGP and Iceland University explored microbial life buried hundreds, even thousands, of meters within the basaltic rocks of Iceland, at the heart of its geothermal aquifers. These extreme environments, where temperatures sometimes exceed 100 °C, host an astonishing microbial diversity whose role remains largely unknown.

Using analyses based on environmental DNA sequencing, the researchers compiled an inventory of the bacterial and archaeal communities colonizing these groundwater systems across 22 wells in western Iceland. They identified assemblages dominated by chemo-lithotrophic and thermophilic microorganisms—capable of deriving energy from rocks and inorganic compounds—that could actively contribute to basalt weathering and carbon storage.

These findings represent a significant step forward in designing experimental microcosms aimed at reproducing interactions between microorganisms, minerals, and fluids under deep subsurface conditions. Identifying the emblematic taxa of these environments—that is, the most representative and metabolically active species—will enable more relevant experiments to study silicate dissolution and CO₂ trapping processes in basaltic formations.

Beyond climate-related implications, these underground ecosystems offer a unique window into the limits of life in extreme conditions, comparable to those that may have existed on early Earth—or even in the subsurface of Mars.

This study thus paves the way for a better understanding of the role of microbes in deep biogeochemical cycles and provides a valuable experimental framework for exploring how life interacts with minerals, from Earth’s depths to planetary environments.