While hiking through Morocco's Dadès Valley, Dr. Rowan Martindale spotted something so unusual that it stopped her in her tracks. The paleoecologist and geobiologist from The University of Texas at Austin was exploring the rugged landscape with fellow researchers, including Stéphane Bodin of Aarhus University, searching for traces of ancient reef ecosystems that once flourished beneath an ocean covering the region millions of years ago. But what Martindale noticed sitting atop ancient ripple marks in deep-water rock formations would challenge everything scientists thought they knew about where ancient microbial life could leave its mark.
"As we're walking up these turbidites, I'm looking around and this beautifully rippled bedding plane caught my eye," Martindale recalled. "I said, 'Stéphane, you need to get back here. These are wrinkle structures!'"
Wrinkle structures are small ridges and depressions formed when microbial communities—algae and bacteria—grow into mats across sandy sediment, binding it together and leaving distinctive textures behind. These delicate features are valuable to scientists because they provide evidence of ancient microbial life. But here's the catch: wrinkle structures are fragile. Once animals began actively burrowing through seafloor sediments hundreds of millions of years ago, these tender textures were typically destroyed before they could fossilize. That's why they're uncommon in rocks younger than about 540 million years old—and why they're usually found in shallow coastal environments where sunlight fuels photosynthetic algae.
The rocks Martindale was examining presented a major puzzle. The turbidites containing these wrinkle structures had formed in deep water, at least 180 meters below the ocean surface. At those depths, sunlight cannot penetrate, making it impossible for photosynthetic algae to survive. If sun-dependent microbes couldn't have created the structures, what did?
Previous reports of wrinkle structures in ancient deep-water turbidites had been controversial and widely debated. The age of these rocks made the mystery even more surprising. They formed roughly 180 million years ago, during the Jurassic period, when seafloor animals were abundant and constantly disturbing sediment—activity that typically destroys delicate microbial textures before they can be preserved.
Martindale knew extraordinary claims required extraordinary evidence. "Let's go through every single piece of evidence that we can find to be sure that these are wrinkle structures in turbidites," she said, since such structures, usually photosynthetic in origin, "shouldn't be in this deep-water setting."
The team carefully investigated the rocks. Their analysis revealed elevated concentrations of carbon in sediment layers directly beneath the wrinkles—often a signature of biological activity. Then they looked to the modern ocean for answers. Video footage from remotely operated submersibles showed that microbial mats can form even far below the sunlit zone, built not by photosynthesis but by chemosynthetic bacteria that generate energy from chemical reactions using compounds like hydrogen sulfide or methane.
When the geological evidence, chemical data, and modern seafloor observations were considered together, the researchers concluded they had identified chemosynthetic wrinkle structures preserved in the rock record—evidence of life thriving where sunlight never reaches. It turns out the deep ocean, long thought of as barren, may hold more secrets about ancient life than we ever imagined.
The discovery opens new possibilities for understanding where life can take hold—and suggests that even in the most unlikely places, life finds a way.