Earth's oldest architects
On the expansive tidal flats of Bigeumdo island, a part of the Shinan Dadohae UNESCO Biosphere Reserve, a deep biological process is quietly taking place. Here, vast communities of microorganisms, primarily cyanobacteria, form gelatinous carpets known as microbial mats. These mats are like Earth's earliest ecosystems. The microbes secrete sticky substances called extracellular polymeric substances (EPS) that trap and bind sediment particles like sand and silt. This activity, combined with the precipitation of minerals, builds up thin layers day by day. Over long periods, these layers lithify, or turn to stone, creating laminated structures called stromatolites.
The structures on Bigeumdo are living rocks. Fossilized stromatolites are the most ancient and common macroscopic evidence of life, with some examples dating back 3.5 billion years. The cyanobacteria within these ancient structures were responsible for one of the most significant changes in Earth's history: the Great Oxygenation Event. Through photosynthesis, they steadily released oxygen, transforming the planet's atmosphere and paving the way for complex life to evolve. Observing the Bigeumdo mats allows a direct view of the fundamental processes that built the world we know today. The very same mechanisms that operated in the Precambrian seas are visible in the daily cycle of tidal immersion and sunlit exposure on these South Korean flats.
Understanding the dolomite problem
The Bigeumdo mats show more than the past; they provide clues to a long-standing geological puzzle known as the "dolomite problem." Dolomite is a calcium magnesium carbonate mineral that is abundant in the ancient rock record but rare in modern environments. Scientists have long debated the exact conditions required for its formation. Research from other modern microbial mats, such as those in the coastal sabkhas (salt flats) of Qatar and Abu Dhabi, shows a direct link between microbial activity and dolomite precipitation.
Within the complex chemical micro-environment of the mat, the metabolic processes of bacteria alter the water chemistry, creating conditions favorable for magnesium to incorporate into the carbonate mineral structure. The exopolymeric substances (EPS) secreted by the microbes act as a template, facilitating the formation of dolomite crystals. The presence of active dolomite formation in places like Bigeumdo helps geologists understand how massive dolomite rock formations, like Italy's Dolomite Mountains, could have formed in the geological past. By studying the specific microbial communities and environmental fluctuations on these tidal flats, scientists can refine models of ancient marine chemistry and the bio-geological forces that have shaped the planet's surface.