Far beneath the reach of sunlight, intriguing markings in Moroccan stone hint at a history of life that was long believed to have been erased by the relentless passage of time. This significant discovery challenges the prevailing notions among scientists regarding the survival of delicate remnants from early ecosystems and suggests new avenues in the search for these biological traces.
These markings manifest as diminutive ridges that have been preserved within deep-water layers of sand and mud, settled approximately 590 feet (or 180 meters) below the ocean's surface. Along the Dadès Valley in Morocco, researchers observed rippled slabs that exhibited additional small ridges atop wave-like grooves, offering a fascinating glimpse into the geological and biological past.
The study, spearheaded by Dr. Rowan Martindale, an Earth scientist at the University of Texas at Austin, delves into how seafloors can retain evidence of ancient life. Dr. Martindale's research concentrates on reefs and microbial ecosystems, employing a blend of field observations and laboratory analyses to draw meaningful conclusions. This methodological approach was critical, particularly because the texture of the rocks appeared too dynamic to preserve microbial mats—layered structures formed by the accumulation of microorganisms.
Wrinkle structures, characterized by ridges and small pits, develop on sandy surfaces as microbes spread across moist sediment. A microbial mat, which is essentially a sticky layer of microorganisms that binds together sediment grains, can effectively trap sand and solidify the uppermost millimeters of sediment. Most wrinkles are typically between 1 to 10 millimeters in size, making them susceptible to disruption by burrowing organisms. Given that sunlight plays a crucial role in the lifecycle of many mat builders, scientists have primarily anticipated the presence of such structures in shallow waters and tidal flats.
However, the Moroccan ripples formed in turbidites—deep-water sediment beds created by dense sediment flows—rather than typical beach sands. During calmer periods, sediment clouds descended and settled rapidly, resulting in layered sand capped with mud. These deposits date back approximately 180 million years to a time when seafloor organisms thrived, complicating the assumption of a photosynthetic origin for the observed structures and providing a formidable challenge in understanding how these wrinkles could have survived.
Dr. Martindale encouraged her team to rigorously analyze the textures as a definitive test. She emphasized the importance of meticulously examining every piece of evidence to ascertain that these were, in fact, wrinkle structures found in turbidites. By tracking sediment layers, ripple forms, and the locations of burrows on the rock, the researchers were able to confirm the beds as turbidites. Without such contextual understanding, superficially similar wrinkles might simply stem from flow deformation, devoid of any biological significance.
The study's chemical analyses revealed an accumulation of organic carbon just beneath the wrinkled surface, rather than being evenly distributed, indicating the presence of biological material. Microscope examinations at UT Austin confirmed that the wrinkles affected only the uppermost 2 millimeters of sediment, consistent with the characteristics of a microbial mat. While carbon alone does not identify the specific microbes involved, it bolsters the hypothesis that biological activity occurred at the sediment-water interface.
In the depths of the ocean, certain bacteria possess the ability to create their own food through a process known as chemosynthesis, deriving energy from chemical reactions rather than sunlight, particularly utilizing sulfide compounds. The research team combined their chemical findings with submersible video evidence, demonstrating that microbial mats can extend well beyond the sunlit zones of the ocean. This modern understanding of microbial ecosystems enabled them to propose that the mat builders in Morocco derived their energy from chemicals either carried or released by the sedimentary beds.
Turbidity flows can entomb fresh organic matter, leading to oxygen depletion in the water trapped between sediment grains. As microbes decompose this organic material, they may produce hydrogen sulfide, a toxic byproduct that poses risks to many marine organisms. Elevated levels of sulfide can inhibit grazing and burrowing activities, allowing microbial mats to persist and potentially wrinkle when bottom currents disturb them. The specific conditions required for such preservation can vary, explaining why some outcrops exhibit pronounced wrinkles while others do not.
Even when mats are formed, subsequent sediment flows often scour the surface, erasing the wrinkles before the sediment solidifies into rock. For preservation to occur, lithification—the process of sediment hardening into rock through mineral cementation—must take place before erosion can erase the surface features. Intervals of calm between sediment flows allow mats to dry slightly, crack into small ridges, and become capped with thin layers of mud, creating a taphonomic window where preservation becomes more feasible on active seafloors.
The discovery of wrinkles in other deep-sea rocks has sparked debate among geologists, many of whom previously assumed that deep sedimentary beds were not conducive to preserving biological evidence. The findings from this study introduce new criteria for evaluating potential biological origins of wrinkle structures, emphasizing the importance of integrating layer characteristics, chemical composition, and modern analogs rather than relying solely on shape. According to Dr. Martindale, "Wrinkle structures are really important pieces of evidence in the early evolution of life." By recognizing turbidites as potential habitats for microbial mats, researchers can revisit historical outcrops and explore new basins for hidden ecosystems powered by chemical energy.
Ultimately, the Moroccan wrinkles, alongside laboratory evidence, underscore the potential for deep-seafloors to preserve microbial activity under favorable chemical conditions. Dr. Martindale plans to conduct laboratory experiments to observe how mats wrinkle in controlled sediment flows while emphasizing the need for caution when interpreting similar textures that lack carbon. The study, which provides important insights into the preservation of early life, is published in the journal Geology.
As reported by earth.com.
