Stromatolites are microorganisms that form carpets and layers, typically made up of cyanobacteria. They were thought to be extinct until a living colony was found in Australia. These organisms generate oxygen and lime, which helped fill the atmosphere with oxygen and fossilize the stromatolites. Modern colonies are found in remote areas with highly saline and warm water. Fossil stromatolites have distinctive layers and mineral deposits.
A stromatolite is an accumulated mass of microorganisms that have grown so closely together that they form a carpet. Stromatolites typically form in layers, creating a characteristic layered appearance, and are a topic of intense interest among geologists. Until the 20th century, the only evidence of stromatolites was in fossil form and scientists assumed these unique biofilms were extinct. However, a colony of living stromatolites was discovered in Shark Bay, Australia, which shocked the scientific world.
Typically, the microorganisms in a stromatolite are cyanobacteria, also known as blue-green algae. Living in colony form is very beneficial to these organisms and numerous examples of microorganisms living in similar colonies can be found throughout the world. A single stromatolite can take thousands of years to form, layer by layer, and can appear in a variety of shapes; many stromatolites look like columns, but they can also form into discs, pyramids, and rings like giant misshapen donuts.
Cyanobacteria thrive where other organisms cannot, and some scientists believe that cyanobacteria and stromatolites are likely responsible for the modern survival atmosphere. These organisms generate energy using carbon dioxide and sunlight, and the byproducts are oxygen and calcium carbonate, also known as lime. The presence of massive amounts of stromatolites on Earth likely helped fill the atmosphere with oxygen, while the generation of lime ensured they would fossilize for people to look at in the future.
Modern living stromatolite colonies are typically found in areas with highly saline and very warm water, mimicking the conditions under which stromatolites survived during the Precambrian era. These carpets of bacteria are very fragile, which may explain why modern colonies have been found in remote areas, far from the reach of humans and grazing animals that could harm them. The Shark Bay colony has in fact been designated a World Heritage Site, recognizing its uniqueness.
In fossil form, a stromatolite has distinctive layers of flake material, often forming over hills and hummocks. It is also common to find deposits of various minerals between the strata, providing clues as to when they were formed and in what condition they were. Many fossil stromatolites are quite colorful, with bands of intense color between more faded layers, and are popular collector’s items.
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