Fracking has mostly been studied because of what it can potentially do to the surface environment. The chemicals used in fracking fluid, as well as the gas and brines that can come back up the wells, all pose environmental risks that have to be managed. What’s often not considered is that the well is a bit like a two-way street. The fracking fluid, which is anything but sterile when injected, also contaminates the environment deep under the Earth’s crust.

A new study, released this week by Nature Microbiology reveals that fracking creates an entire ecosystem 2.5km below the Earth’s surface, one that can persist for at least a year after the frack. And the microbes that thrive there may actually have implications for the production and durability of the fracking wells.

The people behind the work (14 of them at three different institutions) took a relatively simple approach: sample the fracking fluid at a couple of wells before it’s sent underground, then sample the fluid that comes back up the wells at various time points, including over 300 days after the fracking. The sampling included a look at the organic chemicals in the fluids, and DNA sequencing that’s sufficient to reconstruct entire genomes from anything present.