The fossil record of cyanobacteria

Abstract

Summary: Fossil evidence of cyanobacteria, represented in the geological record by microbially laminated stromatolites, cyanobacterial and cyanobacterium-like microscopic fossils, and carbon isotopic data consistent with the presence of Rubisco-mediated CO 2 -fixation, extends back to ∼3,500 million years ago. The most abundant and best-documented fossil cyanobacteria, known from thousands of specimens preserved in several hundred geological units, belong to five taxonomic families: the Oscillatoriaceae, Nostocaceae, Chroococcaceae, Entophysalidaceae and Pleurocapsaceae. As documented by the essentially identical morphologies, life cycles, and ecologic settings of such fossils and their modern counterparts, members of these families have exhibited extreme evolutionary stasis over enormous segments of geological time. Because of the incompleteness of the fossil record, however, such data do not resolve the time of origin of O 2 -producing cyanobacteria from their anoxygenic, bacterial, evolutionary precursors. Though it is well established that Earth's ecosystem has included autotrophs since its very early stages, available data indicate only that O 2 -producing photoautotrophic cyanobacteria originated earlier than the Great Oxidation Event at ∼2,450 million years ago; that such microbes were evidently extant by ∼2,700 million years ago; and that the origin of oxygenic photosynthesis may date from as early as, or even earlier than, 3,500 million years ago.