Introduction: Stromatolites

Stromatolites are the oldest known fossils, dating back more than 3 billion years. They are in the form of colonial structures formed by photosynthesizing cyannobacteria and other microbes. Cyanobacteria are prokaryotes, which are primitive organisms that are lacking in cellular nucleii.  Stromatolites thrived in warm aquatic environments and were one of the major reef formers of the past.  It is thought that Cyannobacteria was one of the main factors responsible for the creation of earth's oxygen atmosphere.  They dominated as the primary lifeform on earth for over 2 billion years. Presently, stromatolites are rare and nearly extinct, living a precarious existence in only a few localities worldwide.
above: cartoon of stromatolites (