Not all microbes are created equal. Some of them are particularly resilient, and can live without sunlight in soaring temperatures at perpetually dark depths, including within Earth’s crust itself.

It has long been thought that extremely hardy organisms should only be found in extreme environments, but a new study, published in the Journal of Geophysical Research: Biogeosciences reveals that, sometimes, certain mischievous microbes turn up where they shouldn’t be. Methane-producing microbes, those often found in deep-sea hydrothermal vent systems, have just been discovered in a set of freshwater springs in Sonoma County, California.

The freshwater emerges up through a set of serpentinized rocks, a geological alteration feature that indicates that circulating, high-temperature, high-pH fluids have been moving through the region. Active serpentinization processes often occur deep underground and within oceanic crust, and the microbes living in these areas use its chemical byproducts to produce energy. The fact that they now clearly exist at the surface too is thoroughly unorthodox.

“As our technology’s expanding, we’re able to look outside of the box a little to capture some of these groups [of microbes],” Matt Schrenk, a microbiologist at Michigan State University in East Lansing, Michigan, who was not involved in the study, said in a statement. “As we’re beginning to look into some of these natural environments [deep underground], our view of the microbial world, and of life in general, is really expanding.”

Previous analysis of the water from the area suggested that the high concentrations of methane may be down to microbes rather than non-biological chemical processes, including active serpentinization. In order to confirm this, water samples were taken back to a laboratory, and the team exposed them to a variety of conditions.

In the samples that were sterilized, no methane was ultimately produced; conversely, samples with live microbes contained up to 650 percent more methane than the sterilized ones. With the serpentinization reactions removed from the equation, it was concluded that a set of microbes in the water were responsible for methane production, also known as methanogenesis.

These methane-detecting organisms likely belong to the archaea domain, single-celled microorganisms that, despite having similar ecological roles to bacteria, are in fact physiologically distinct.

This discovery brings with it several revelations. Firstly, methanogens – organisms that manufacture methane – are likely found in a wider variety of environments around the world, and possibly on other worlds, than previously thought.

^{The Cedars is a small, isolated set of springs flowing out of a large patch of red rock in Sonoma County, California. The Cedars is one of the few easily-accessible sites of active serpentinization on land. Lukas Kohl}

Methane has recently been detected in Mars’ atmosphere, and many have suggested that serpentinization is the culprit. This new microbial discovery suggests that it’s possible that archaea at or near the Martian surface, perhaps within patches of high-pH water, may be responsible for pumping methane into the atmosphere instead.

Secondly, as these microorganisms appear to be able to convert carbon dioxide into methane as part of their metabolic processes, researchers in the area may have to rethink their carbon sequestration efforts. Using technology to remove carbon dioxide from the atmosphere is all well and good when it comes to militating against climate change, but if this is locked up in this methanogen-containing soil as a form of carbonate, it will be rapidly converted it to methane – a shorter-lasting but far more powerful greenhouse gas.

^{Image in text: Another example of a methane-generating microorganism, typically of the archaea domain. Maryland Astrobiology Consortium, NASA, and STScI}