Cyanobacteria Making a Contribution
Cyanobacteria, also known as "blue-green algae", are some of the longest living organisms on planet Earth. Originating in the Precambrian they span the entire duration of the Phanerozoic Eon. They are recognizable today, as well as in the rock record, as microscopic filamentous organisms. These organisms were likely the first photosynthetic organisms and were responsible for "polluting" the originally carbon dioxide (CO2) rich atmosphere with the oxygen we breathe today.
Stromatolites are commonly mistaken as fossils, but are actually sedimentary structures. They form when mats of cyanobacteria, commonly called "algal mats", bind and hold sediment that is washed over them by waves. Over time sediment buildups can begin to form domal structures similar to the shape of a person's head. Stromatolites are easily recognizable in the rock record because they preserve their original geometries and layers created by many rounds of sediment bound by cyanobacteria.
Stromatolites in the Precambrian were able to form in many parts of the ocean. As time went on and grazers began to develop (gastropods, echinoids, and others) stromatolites began to form only in hypersaline conditions. Water in these areas of elevated salinity wonl't support most forms of life accept those that are highly adaptable, like cyanobacteria, rendering them safe from predators.