Stromatolites form when cyanobacteria -- among the simplest organisms capable of photosynthesis -- trap fine particles of sand, crushed shell, and sediment in their sticky filaments. The bacteria cement these particles with calcium carbonate they produce themselves, building the structure upward at roughly 0.5 mm per year. Some columns at Hamelin Pool stand 1.5 meters tall, representing thousands of years of growth. The living stromatolites here resemble fossils found across the planet dating back 3.5 billion years. At Marble Bar in the Pilbara region of Western Australia, fossil stromatolites reach 50 meters high and 30 meters across, estimated to be over three billion years old. The cyanobacteria at Hamelin Pool are direct descendants of those ancient photosynthesizers -- organisms that converted a hostile, oxygen-poor early Earth into one that could eventually support complex life.

Stromatolites were once common in shallow seas worldwide, but competition and grazing by more complex organisms made them increasingly rare. At Hamelin Pool, a quirk of geography and chemistry has kept them alive. The Wooramel Seagrass Bank, an underwater prairie 130 km long, shelters the inner lagoon and restricts water exchange with the open ocean. This makes Hamelin Pool hypersaline -- roughly double the salinity of normal seawater. The extreme salt concentration inhibits the snails, sea urchins, and other creatures that elsewhere would devour the slow-growing bacteria. Three billion individuals per square meter colonize the sea bed, free to build undisturbed. Three basic forms emerge: sub-tidal columns that remain permanently submerged, intertidal anvil or mushroom shapes exposed at low tide, and flat algal mats that look like black mud but are living stromatolite in their own right.

The stromatolites of Hamelin Pool were discovered in 1956 by surveyors working for an oil exploration company -- the first living examples ever identified of structures built by cyanobacteria. The reserve that now protects them covers 1,270 square kilometers of marine habitat within the UNESCO World Heritage-listed Shark Bay. Hamelin Pool was named for Jacques Felix Emmanuel Hamelin, the French naval officer who captained the Naturaliste during the Baudin expedition of 1801-03 and whose crew first charted much of this coastline. The historic Hamelin Pool Telegraph Station, built in 1884, sits adjacent to the reserve. Its museum includes what is said to be the only stromatolite living in captivity -- a specimen kept alive in an aquarium. The old post office, first constructed in 1886, now serves as the local community post office and phone box.

Access is simple and free. A side road from Highway 353, about 30 km west of the Overlander Roadhouse on the North West Coastal Highway, leads to the telegraph station grounds. From there, an interpretive boardwalk extends over the shallows, allowing visitors to examine the stromatolite formations without stepping on them -- the structures are fragile, and even a footprint can destroy centuries of growth. Hutchinson Island and Pelican Island lie within the reserve's boundaries. The Peron Peninsula separates Hamelin Pool from the western waters of Shark Bay, while Faure Island and L'Haridon Bight define its northern edge. It is a plain, sunlit, utterly unremarkable-looking stretch of shallow water, and it is as close as you can get to standing in the Precambrian.