While hiking through Morocco's Dadès Valley, Dr. Rowan Martindale spotted something so unusual that it immediately caught her attention. Martindale, a paleoecologist and geobiologist at The University of Texas at Austin, was exploring with fellow researchers, including Stéphane Bodin of Aarhus University, to investigate ancient reef ecosystems. To get to those reefs, they had to cross layers of rock called turbidites - deposits from underwater avalanches. Ripple marks are common there, but Martindale noticed something sitting on top: wrinkle structures, small ridges and depressions formed by microbial mats.

Wrinkle structures are evidence of ancient microbial life, but they're fragile. Once animals started burrowing through seafloor sediments hundreds of millions of years ago, these features were usually destroyed. As a result, they're rare in rocks younger than about 540 million years old and are mostly found in shallow coastal environments where sunlight supports photosynthetic algae. The rocks Martindale was examining, however, formed in deep water at least 180 meters (590 feet) below the surface, where sunlight can't reach. That's a problem: if sunlight-dependent microbes couldn't have created them, what did?

The turbidites formed roughly 180 million years ago, when seafloor animals were abundant and constantly disturbing sediment - exactly the kind of activity that destroys microbial textures. Everything said these wrinkle structures shouldn't be there. Martindale and her team set out to confirm both the environment and the biological origin. They verified the layers were deep-water turbidites, then found elevated carbon concentrations beneath the wrinkles - a chemical signature of biological activity.

Turning to modern oceans, the researchers found video footage from remotely operated submersibles showing microbial mats forming far below the photic zone, powered by chemosynthetic bacteria that use chemical reactions instead of sunlight. The team concluded they had identified chemosynthetic wrinkle structures in the rock record. Their proposed explanation: turbidite flows delivered nutrients to the deep seafloor; as organic matter decomposed, oxygen levels dropped, creating conditions for chemosynthetic microbes. Between debris flows, bacterial mats spread and developed wrinkles, occasionally getting buried and preserved.

Martindale hopes future lab experiments will clarify how these structures form in deep water. The discovery suggests geologists may need to revisit environments previously dismissed as unlikely to preserve evidence of ancient microbial life. "Wrinkle structures are really important pieces of evidence in the early evolution of life," says Martindale. By ignoring their possible presence in turbidites, "we might be missing out on a key piece of history of microbial life."