Stromatolites

In the hyper-saline water of Hamelin Pool at the base of Shark Bay in W.A. the rocks aren't quite what the appear to be. They are living things, Stromatolites, which are the oldest living organisms on the planet. Some scientists believe they were the first living things on mother earth. Dr Phillip Playford is a scientist and historian who has studied every facet of stromatolites.Hamelin Pool is the location of the best example in the world of living marine stromatolites. The water of Hamelin Bay is twice as saline as usual sea water because of a bar across the Bay's entrance and rapid evaporation from the shallow water. Most living animals, which feed on the bacteria and algae of which stromatolites are composed, cannot tolerate such saline conditions. As a result stromatolites can grow here successfully, undisturbed. Most stromatolites are extremely slow growing. Those in Hamelin Pool grow at a maximum of .3mm a year, so those which are up to a metre high are hundreds if not thousands of years old. Stromatolites are formed through the activity of primitive unicellular organisms: cyanobacteria (which used to be called blue-green algae) and other algae. These grow through sediment and sand, binding the sedimentary particles together, resulting in successive layers which, over a long period of time, harden to form rock. For at least three-quarters of the earth's history stromatolites were the main reef building organisms, constructing large masses of calcium carbonate.However their most important role in the history of the earth has been that of contributing oxygen to the earth's atmosphere. The organisms which construct stromatolites are photosynthetic. They take carbon dioxide and water to produce carbohydrates, and in doing this they liberate oxygen into the atmosphere.When stromatolites first appeared on earth about 3.5 billion years ago there was little or no oxygen in the atmosphere. It was through the oxygen-generating activity of stromatolites that other animal life on earth was able to develop. Conversely, it is believed that the decline in numbers of stromatolites is related to the evolution of animals that consumed cyanobacteria and algae.Stromatolite fossils are evidence of the earliest life on the earth. Western Australia perhaps has the best stromatolite fossils, giving a record through the eons of time. Fossils of the earliest known stromatolites, about 3.5 billion years old, are to be found near Marble Bar in the Pilbara. Hamelin Pool gives an indication of what the earth may have looked like 3.5 billion years ago when stromatolites were widespread. Because of their range and numbers it is a place of great interest to botanists and geologists alike. A jetty has been constructed allowing the stromatolites to be viewed without doing them irreparable damage.It's a humbling thought that all life on this planet could have started from something so simple as the blue-green algae which created these rocks millions of years ago.Dr Playford is a consultant for the Department of Minerals and Energy, and a former Director of the Geological Survey.Stromatolite fossils can be viewed at the Western Australian Museum, Perth, W.A.