Scientists say ancient deep-sea microbial life may have left behind a surprising fossil signal in rocks from Morocco, challenging a long-held assumption about where these structures can form. The team found wrinkle-like textures in sediments laid down about 180 million years ago in deep water, far below the reach of sunlight. That matters because researchers usually link these features to shallow seafloors, where light supports photosynthetic microbial mats.
The discovery began when Rowan Martindale, a paleoecologist and geobiologist at the University of Texas at Austin, noticed unusual ridges and wrinkles on top of rippled sediment layers while working in the Dadès Valley in Morocco’s Central High Atlas Mountains. She and her colleagues had been studying ancient reef systems in the area when the textures stood out as something different from ordinary ripple marks.
Why the Discovery Looked So Unlikely
Scientists call these features wrinkle structures. They usually form when algae and microbial communities grow in mats across sandy seafloors, creating tiny ridges and pits. Researchers rarely find them in younger rocks because animals churn up sediments, destroying these delicate textures. ScienceDaily reports that wrinkle structures are uncommon in rocks younger than about 540 million years old, after animal life began actively disturbing the seafloor.
That made the Moroccan find hard to explain. The team identified the host rocks as turbidites, deposits left by dense underwater debris flows. According to the report, these sediments formed at depths of at least 180 meters, too deep for sunlight-dependent algae to survive. On top of that, the rocks date to a period when animals already disturbed seafloors worldwide, which should have reduced the odds of preserving fragile microbial textures.
Chemical Clues Pointed to Life in the Dark
To test whether the wrinkles were truly biological, the researchers examined the surrounding rock layers and analyzed sediment chemistry. They found elevated carbon levels just beneath the wrinkle surfaces, a clue that often points to a biological origin. They also compared the structures with modern observations from deep-ocean environments below the photic zone, where microbial mats can still form in the absence of sunlight.
The team concluded that ancient deep-sea microbial life likely produced these mats through chemosynthesis rather than photosynthesis. In this process, microbes obtain energy from chemical reactions rather than sunlight. The researchers propose that turbidite flows carried nutrients and organic material into deep water while also lowering oxygen levels in nearby sediments. During quieter periods between flows, chemosynthetic bacteria could spread across the seafloor, form mats, and create the wrinkled textures later preserved in rock.
A New Place to Search for Early Life
The study suggests geologists may need to rethink where they look for fossil traces of microbial ecosystems. If chemosynthetic mats can create wrinkle structures in deep-water sediments, then researchers may have overlooked evidence of ancient deep-sea microbial life in environments once considered unlikely candidates. Martindale said the finding could reveal “a key piece of history of microbial life” that scientists have missed by focusing too narrowly on shallow-water settings.
The work appeared in the journal Geology and lists Rowan C. Martindale, Sinjini Sinha, Travis N. Stone, Tanner Fonville, Stéphane Bodin, François-Nicolas Krencker, Peter Girguis, Crispin T.S. Little, and Lahcen Kabiri as authors. The result does not just add one unusual fossil site. It broadens the map for future searches by showing that life in the dark ocean may have left visible fingerprints in places scientists did not expect to find them.