What is a Stromatolite?

A stromatolite is an accreted mass of microorganisms which have grown so closely together that they form a mat. Stromatolites typically form in layers, creating a characteristic stratified look, and they are a topic of intense interest among geologists. Until the 20th century, the only evidence of stromatolites was in fossil form, and scientists presumed that these unique biofilms were extinct. However, in Shark Bay, Australia, a colony of living stromatolites was discovered, rocking the scientific world. Typically, the microorganisms in a stromatolite are cyanobacteria, also known as blue-green algae. Living in the form of a colony is highly advantageous to these organisms, and numerous examples of microorganisms living in similar colonies can be found all over the world. A single stromatolite can take thousands of years to form, layer by layer, and it may appear in a variety of shapes; many stromatolites look like columns, but they can also form in discs, pyramids, and rings like ...  more

This is a transcript of a QuickTime movie (0.7 MB) recorded in the Pilbara in 2005. Abby Allwood, from the Australian Centre for Astrobiology, defines the term stromatolite. Transcript: ‘Stromatolite’ is a term that has interpretation associated with it, which is unfortunate. It would be nice to have an easy term that was non interpretative. ‘Stromatolite’ does mean a laminated sedimentary structure created by organisms or at least with the influence of organisms.  more

A stromatolite is produced by cyanobacteria. The distinctive layers are produced as calcium carbonate is precipitated over the growing mat of bacterial filaments. Photosynthesis in the bacteria depletes carbon dioxide in the surrounding water and makes it less acidic thus initiating the precipitation of the calcium carbonate. The minerals, along with grains of sediment precipitating from the water become trapped within the sticky layer of mucilage that surrounds the bacterial colonies. As the colony continues to grow upwards through the sediment a new layer is formed. As this process occurs over and over again, the layers of sediment are created.  more