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While features of some ancient apparent 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.
Algal mats are one of many types of microbial mat that forms on the surface of water or rocks. They are typically composed of blue-green cyanobacteria and sediments. Formation occurs when alternating layers of blue-green bacteria and sediments are deposited or grow in place, creating dark-laminated layers. Stromatolites are prime examples of ...
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.
Stromatolites are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria. [108] Stromatolites provide some of the most ancient fossil records of life on Earth, dating back more than 3.5 billion years ago. [109]
The age of Earth is about 4.54 billion years; [7] [33] [34] the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago according to the stromatolite record. [35] Some computer models suggest life began as early as 4.5 billion years ago. [36] [37] The oldest evidence of life is indirect in the form of isotopic ...
The stromatolites found today are almost all carbonate rocks (made of limestone), but these structures are mostly composed of the minerals gypsum and halite (rock salt), Hynek said.
3.4 billion year-old stromatolites from the Warrawoona Group, Western Australia. While the origin of Precambrian stromatolites is a heavily debated topic in geobiology, [50] stromatolites from Warrawoona are hypothesized to have been formed by ancient communities of microbes. [51]
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