Kidd Creek Mine in Ontario, Canada, is home to some of the oldest-known water on the planet – and now, it seems, the creek's sulfate and hydrogen-rich water can host microbial life.

Previous studies determined that the water has been trapped 2.4 kilometers (1.5 miles) below the surface in the creek's Precambrian rock for millions (and, perhaps, billions) of years. Last month, a study published in Geomicrobiology Journal discovered the existence of microbial life untouched by water from the surface.

Researchers from the University of Toronto, Canada, found microbial cells amongst the sediment in samples collected via two boreholes, which naturally discharge fracture water. The results add more weight to the collection of evidence that there is a subsurface biosphere in the Earth's crust – an area thought to be hostile to life – that has very little (if any) interplay with what goes on above.

In December 2018, a decade-long project exposed a deep biosphere comprised of billions of microbes living miles below the subsurface – in fact, they suspect as much as 70 percent of all microorganisms that live on Earth exist here underground in environments believed to be too hot, too dark, and with too little nutrients to sustain living things (even those as small as a nematode).

As a collective, it is believed these microbes create 15 to 23 billion tonnes of carbon – which is 245 to 385 times greater than the carbon mass of humans above the surface.

The scientists involved described it as a "subterranean Galapagos", comprising of bacteria, archaea (microbes without a membrane-bound nucleus), and eukarya (microbes and multicellular organisms with a nucleus and membrane-bound organelles). Unlike their surface-dwelling relatives, these microbes live on near-geologic timescales. Some subsist on nothing more than energy from rocks.

These microorganisms (and their diversity) are an understudied phenomenon that needs far more exploration, but this early evidence suggests levels of genetic difference could be as far-reaching as that above surface – and perhaps, even more so.

As for those that exist in Kidd Creek Mine, the team at the University of Toronto analyzed their metabolic activity by measuring how quickly they metabolized certain food types. The results show that the community of microbes collected were almost all sulfate reducers. That is: microorganisms that perform anaerobic respiration that uses sulfate, reducing the substance to hydrogen sulfide (H₂S).

"The identification of sulfate-reducing organisms in these fluids, both in the geologic past and in the present day (this study) is an important finding extending our understanding of the deep subsurface biosphere," write the study authors.

"Understanding when these fracture fluids were colonized by life remains an outstanding question but can begin to be constrained by application of a variety of groundwater dating approaches."

While the results raise questions over how long extant microbial ecosystems (or biomarkers of past life) can last, the researchers hope the findings can be used to enhance our understanding of Earth's deep biosphere and attempts to find extant and extinct life on Mars – or, indeed, anywhere else in the Solar System.

[H/T: The Scientist]