Mat-forming cyanobacteria have a particularly long history. Some of these organisms form laminated,
lithified structures called stromatolites that are well represented in the fossil record all the way back
to the Precambrian. The fossils contain layered, filament-like inclusions and bear striking resemblance
to living stromatolites that occur today in a small number of marine habitats, and also in certain
lakes. The stromatolite communities are thought to have been the main primary producers on Earth for
more than 1 billion years throughout the Proterozoic, and a major contributor to atmospheric oxygen that
in turn set the stage for the rise of oxygen-requiring microbes and animals. They are less successful today,
in part, because of the presence of grazing animals, including crustacean zoobenthos and zooplankton.