An ancient world
In the sheltered waters of Porto Pim Bay on Faial Island, a remarkable geological and biological phenomenon exists. Here you can find living marine stromatolites, which are layered structures created by communities of microorganisms. These structures are living fossils because their ancestors were one of the earliest forms of life on Earth, dating back as far as 3.5 billion years. For billions of years, before the evolution of more complex life, vast reefs of stromatolites dominated shallow seas worldwide.
The structures in Porto Pim are formed by cyanobacteria, single-celled microbes that photosynthesize. In a process that continues today, these bacteria secrete sticky compounds that trap and bind sand and other sediments. Layer by layer, over long periods, these microbial mats build up the stony, laminated structures characteristic of stromatolites. Modern marine stromatolites are exceedingly rare, typically found only in extreme environments like hypersaline lagoons where high salt levels prevent grazing animals from eating the microbial mats. The presence of this community in the normal salinity of Porto Pim Bay makes it an important site for scientific study.
The Azorean volcanic context
The Azores archipelago sits at the triple junction of the North American, Eurasian, and African tectonic plates, a location of intense and ongoing volcanic activity. This unique geological setting shapes the chemistry of the coastal waters. The sediments of the Azores Platform are a mixture of biogenic material and detrital volcanic matter. This specific geochemical environment likely contributes to the conditions that allow the Porto Pim stromatolites to thrive.
The stromatolite structures in the bay are shaped like bread loaves, each about 12 to 15 cm high and 40 to 50 cm long. They are fully exposed during low tide and are oriented in the same direction by the tidal currents. While cyanobacteria are the primary builders, the structures host a diverse community of other bacteria and archaea. These complex microbial ecosystems are miniature laboratories for understanding how life colonized the planet and fundamentally changed its atmosphere by producing oxygen. The study of these modern communities shows how the earliest life on Earth functioned and created the world we know today.