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stromatolite,layered structures produced by the binding together of sediments by a thin layer of cyanobacteriacyanobacteria
or blue-green algae,
photosynthetic bacteria that contain chlorophyll. For many years they were classified in the plant kingdom along with algae, but discoveries made possible by the electron microscope and new biochemical techniques have shown them to be
..... Click the link for more information. . The layers, which are deposited very slowly, gradually produce rounded or hummocklike formations. Stromatolite fossils are common in Precambrian rocks, and the cyanobacteria associated with them are believed to have been a major contribubutor to the increasing oxygen of the early earth. Stromatolites now are found primarily in environments where high salt levels discourage animals from eating the cyanobacteria.
a dense, layered structure that forms in limestones and dolomites as a result of the presence of colonies of blue-green and other algae. Stromatolites reach several meters in length and 1–2 m in height. They have been traced back to the Proterozoic; Upper Proterozoic and Lower Paleozoic fossils are particularly common. The formation of stromatolites occurs in warm, shallow waters with elevated or decreased salinity. The various morphological types, which evolved during the course of geological time, are used for the biostratigraphic analysis of Upper Proterozoic deposits, in which remains of other organisms are extremely rare.