A survey of groundwater samples drawn from aquifers beneath more than 80,000 square miles of Canadian prairie reveals ancient groundwaters harbor not only diverse and active microbial communities, but also unexpectedly large numbers of microbial cells. Strikingly, some of these microbes seem to produce ‘dark oxygen’ (in the absence of sunlight) in such abundance that the oxygen may nourish not only those microbes, but may leak into the environment and support other oxygen-reliant microbes that can’t produce it themselves.
