Stromatolites (from Greek στρώμα, strōma, mattress, bed, stratum, and λιθος, lithos, rock) 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). They're the oldest living organisms on the planet, and are believed to be the first living organisms on Earth. Morphology A variety… (More on Stromatolite)