Modern stromatolites -- living fossils
Stromatolites in Shark Bay, Western Australia -- exposed (left) and submerged (right).
This extensive field of relict organisms was discovered in 1956. More examples occur in other locations on the ancient shield of western Australia. Map. Western Australia boasts some of the oldest known examples of stromatolites (3.45 billion years old), occurring as fossils in the Pilbara region between Marble Bar and Port Hedland. More recently, stromatolite colonies have been discovered in locations such as the Bahamas, the Indian Ocean, Yellowstone National Park, and Poza Azul lake at Cuatro Cienegas, Mexico.
At low (left) and higher tides (right).
The water of Hamelin Pool within Shark Bay is twice as saline as typical sea-water because of rapid evaporation from the shallow water, and because a bar across the bay's entrance reduces mixing with normal brine. This hypersaline water is inhospitable to marine animals, which which otherwise would feed on the bacteria that construct stromatolites. As a result stromatolites can grow undisturbed in Shark Bay. Most stromatolites are extremely slow growing. Those in Hamelin Pool grow at a maximum of .3mm a year. This means that those that are up to a metre high are several thousands of years old. More images of stromatolites of Hamelin Pool (Shark Bay) / stromatolites displaying weathering / partly submerged / partly exposed