Cyanobacteria have been linked with the formation of our atmosphere, since they were the first known oxygen-producing life forms on Earth. Stromatolites are actually composed of sediments, such as particles of sand and shells that are continually deposited during tidal fluctuations. These are trapped by filaments of cyanobacteria and algae that grow out through the sediment, reaching for sunlight needed for photosynthesis. Over many years, layers of sediment are bonded together by the mucus secreted by the cyanobacteria and algae. Internally, the algae and cyanobacteria die and leave the bonded layers of sediment as a hard, rock-like skeleton.
Growth rates are extremely slow.
Recent measurements have shown less than half a millimetre annually for the fastest growing stromatolites. This dates some of the Shark Bay structures at over one thousand years old. Hamelin Pool is a unique environment. It's waters contain around twice the salt concentration of normal oceanic waters. Very few plants and animals found in the seas of today can survive in this 'hypersaline' environment.