Microbialites are structures built mainly by cyanobacteria (also known as blue-green bacteria or, less correctly, as blue-green algae). They are still found today, but were once much more common, dominating the fossil record between about 2000 million and 600 million years ago.
Living stromatolites at Shark Bay, Western Australia, showing the laminated structure of a single column and the microscopic cyanobacteria that construct them. Each cyanobacterial filament is about 100th of a millimetre in width. These organisms are rarely preserved in fossil stromatolites, although some have been discovered in chert (silica-rich rock) at other localities in the Pilbara that are about the same age as the Trendall locality.
- Living microbialites are found mainly in saline lakes and hot spring environments, usually in environmental niches that other organisms cannot tolerate.
- Microbes slowly move up through deposited layers to reach light and form a new layer on the outer surface. Older layers within the structure harden into rock.
- The best living microbialites are at Hamelin Pool and Shark Bay in Western Australia.
- Other WA microbialites are found at Lake Clifton near Mandurah, Lake Thetis near Cervantes, Lake Richmond near Rockingham and several lakes on Rottnest Island.
- Microbialites with laminae are known as stromatolites (some Shark Bay ones and most fossils); those with a clotted fabric are thrombolites (Lake Clifton).
- Microbial mats precipitate or trap and bind sediment over long periods of time to make stratiform, domical, columnar, conical, or complexly branching structures.
- Microbialites can range in size from smaller than a little finger to larger than a house. Some branching stromatolites resemble modern corals.
- Many, but not all, microbialite-producing organisms are photosynthetic and produce oxygen as a result of their metabolic activities. Such organisms converted Earth's atmosphere from one dominated by greenhouse gases to one with breathable oxygen.
