Survey of Microbial Composition and Mechanisms of Living Stromatolites of the Bahamas and Australia: Developing Criteria to Determine the Biogenicity of Fossil Stromatolites

A stromatolite is typically defined as a laminated and lithified structure that is the result of microbial activity over the course of time. Fossil stromatolites are relatively abundant; however, modern living stromatolites are rare. Two well-studied examples of living stromatolites include those found in the Exuma Cays of the Bahamas and Shark Bay in Australia. Depending on dominant chemical reactions by bacteria and environmental conditions, accretion and lithification of the stromatolite occurs at intervals. Each layer or lamina of a stromatolite represents a former surface mat of bacteria. As long as cyanobacteria (or other phototrophs) colonize the top surface of the stromatolite, growth is likely to continue. Understanding microbial composition and mechanisms of living stromatolites is crucial to determining the biogenicity of fossil stromatolites. Although there is a paucity of fossilized bacteria in fossil stromatolites, their structural features closely resemble those of living stromatolites. A set of criteria from the study of living and fossil stromatolites has been developed to aid determination of the biogenicity of fossil stromatolites. It was concluded that there is now sufficient evidence for the biogenicity of many stromatolites, even as early as 3.5 Ga, so these need to be understood within the biblical framework of earth history. Discernment of genuine stromatolites in the geologic record may help determine boundaries between Creation Week, pre- Flood and Flood strata. In addition, understanding how various living stromatolites form in different environments provides insight into the pre-Flood environments in which fossil stromatolites grew