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While features of some stromatolites are suggestive of biological activity, others possess features that are more consistent with abiotic (non-biological) precipitation. [17] Finding reliable ways to distinguish between biologically formed and abiotic stromatolites is an active area of research in geology.
Ancient giant stromatolites used to be widespread in Earth’s Precambrian era, which encompasses the early time span of around 4.6 billion to 541 million years ago, but now they are sparsely ...
Evidence for this hypothesis is preserved in both chert and lithified stromatolites. [1] Stromatolites represent large colonies of microorganisms, and are found both in the fossil record and rarely in modern hypersaline environments. A typical stromatolite consists of alternating layers of sediment and microbes.
In moist conditions mats are usually held together by slimy substances secreted by the microorganisms. In many cases some of the bacteria form tangled webs of filaments which make the mat tougher. The best known physical forms are flat mats and stubby pillars called stromatolites, but there are also spherical forms.
The lack of many well-preserved stromatolites has been proposed as a consequence of ongoing diagenesis during formation. [5] Diagenesis is a weathering process where newly deposited sediments lies on top of the old sedimentary bed, buried and compacted, lithified and uplifted to the surface as sedimentary rocks.
Most archean stromatolites older than 3.0 Ga are found in Australia or South Africa. Stratiform stromatolites from the Pilbara Craton have been identified in the 3.47 Ga Mount Ada Basalt. [ 59 ] Barberton, South Africa hosts stratiform stromatolites in the 3.46 Hooggenoeg, 3.42 Kromberg and 3.33 Ga Mendon Formations of the Onverwacht Group .
The Gunflint Chert is composed of biogenic stromatolites. [3] At the time of its discovery in the 1950s, it was the earliest form of life discovered and described in scientific literature, as well as the earliest evidence for photosynthesis. [4] The black layers in the sequence contain microfossils that are 1.9 to 2.3 billion years in age.
Collenia Temporal range: 2400–2100 Ma Pha. Proterozoic Archean Had. Siderian - Rhyacian Section of Collenia undosa stromatolite from 2110 million year old banded iron formation, Biwabik Collenia undosa stromatolite from Precambrian of United States Scientific classification Domain: Bacteria Phylum: Cyanobacteria Family: Spongiostromata Subfamily: Stromatolithi Genus: † Collenia Walcott ...