2.6 billion years ago, during the Precambrian era, cyanobacteria were once very abundant on Earth. At that time, cyanobacteria not only had a large variety and quantity, but also could form unique sedimentary structures during their growth process by combining the gray matter outside their cells with algal filaments to adhere to surrounding carbonate debris. This structure not only helped algae grow, but also enhanced their resistance to seawater invasion. Algae were arranged in layers, growing upward, and their growth rates varied in different seasons and years, leaving behind layers with different densities and shades, including arched, conical, or flat layers. The sedimentary structures formed by them are called stromatolites. Stromatolites formed during this period were very abundant and can be found all over the world.
After the end of the Precambrian era, stromatolites gradually declined. It is speculated that this was because animals appeared on Earth during this period and ate these algae, causing their numbers to rapidly decrease. Even when stromatolites were formed, their scale was very small, and stromatolites were even rarer in strata after the Cambrian era. Modern stromatolites are still widely distributed in shallow sea areas such as the west coast of Australia and the Bahamas Islands in Central America. In other places, although cyanobacteria are very common in lakes and oceans, most of them become food for fish and shrimp, and only when the water body is eutrophic will they break out or proliferate rapidly, causing an algal bloom, but this is completely different from the environment in which stromatolites are formed.