What appear to be rocks submerged in the hyper-saline water of Hamelin Pool at the base of Shark Bay in the Gascoyne region of Western Australia, are not quite rocks. They are living things called stromatolites, created by tiny, single-celled microbes called cyanobacteria (blue-green algae), which are some of the earliest forms of life on earth.

Stromatolites are formed by the growth of layers upon layers of cyanobacteria and sediments that the microbes trap with their sticky mucus layer. These fine particles are cemented together with calcium carbonate produced by the bacteria, thereby building up the stromatolite structures. While they don’t seem to be living, each structure is actually a very slow growing microbial colony that may grow less than 1mm per year.

Photo credit: Kristina D.C. Hoeppner/Flickr