Stromatolites

Stromatolites are layered structures formed in shallow water by biofilms of microorganisms, especially cyanobacteria (commonly known as blue-green algae).

Stromatolites were much more abundant in Precambrian times, but blue-green algae are still alive today (see left). Domain: Bacteria Phylum: Cyanobacteria

Stromatolites are layered accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria (commonly known as blue-green algae).

Very few ancient stromatolites contain fossilized microbes. While features of some stromatolites are suggestive of biological activity, others possess features that are more consistent with "abiotic" (non-organic) precipitation.