Fossil Stromatolites
Stromatolites are cyanobacteria (like algae). Living stromatolite systems are now quite uncommon on earth. They are found in only a few places, like Shark Bay & Lake Clifton in Western Australia. These primitive organisms grow in the shallows producing their own food from water, carbon dioxide, and sunlight - photosynthesis.
In return they produce calcium carbonate (lime) and oxygen.
Early cyanobacteria are believed to have been responsible for generating the oxygen in the Earth's atmosphere.
Stromatolites secreted a thick gel as protection from solar radiation. This gel, in turn, trapped sand and debris from the surf, which together with the secreted lime created the various forms, including domes, cones and complex branching configurations. These structures are highly variable in size, ranging from small delicate digitates to huge domal structures.
Cyanobacteria reached the peak of their distribution some 2.2 billion years ago when they were the most advanced forms of life. In fact, the oldest known stromatolites occur in rocks of the Warrawoona Group of Western Australia and are some 3.4 to 3.5 billion years old.
"Pilbaria perplexa". These stromatolites
had long branching columns.They occur in the "Duck Creek
Dolomite" not far from the iron ore mining town of Paraburdoo in
Western Australia.
Their age is around 2 billion years. They are believed to have grown in a shallow marine lagoon environment with rare periods of emergence.
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"Asperia ashburtonia". These closely
packed columnar stromatolites are from the same location as the above
described "Pilbaria perplexa".
A domal stromatolite from the Proterozoic "Irregully
Formation" in Western Australia. Age is approx. 1.1 billion years.
Asperia digitata formerly named Yelma digitata, from near Wiluna in
Western Australia. The environment in which these small digitates grew, is
believed to have been brackish marshes. They are from the Proterozoic
"Yelma Formation" which has an age of around 1.7 billion years.
"Earaheedia kuleliensis" is from the
Nabberu Basin approx. 500 miles east of Perth. It is from the "Kulele
Limestone", a formation of limestone, shale & fine grained
sandstone with an age of around 1.7 billion years. The stromatolites range
in size from small flat domes a few centimetres across to large bioherms
over 30 metres in length.