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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 oldest stromatolites have been dated to approximately 3.5 billion years old. [18] Stromatolites in Barberton have been dated to about 3.3 billion years. Microfossils found in chert extend the Barberton microfossil record back to 3.5 billion years. All three types of microfossil morphologies are found in cherts.
Scientists have argued for a biological origin of stromatolites due to the presence of organic globule clusters within the thin layers of the stromatolites, of aragonite nanocrystals (both features of current stromatolites), [18] and of other microstructures in older stromatolites that parallel those in younger stromatolites that show strong ...
The stromatolite fossils appear wavy and dome-shaped, are typically 1–4 cm (0.4–1.6 in) high, and were found in iron- and magnesium-rich dolomites that had recently been exposed by melting snow. [39] The surrounding rocks suggest that the stromatolites may have been deposited in a shallow marine environment. [38]
Modern stromatolites are relatively small, Hynek said, whereas ancient stromatolites used to grow to 20 feet (6 meters) tall and 16 to 22 feet (5 to 7 meters) wide, he said.
Allwood has published extensively on characterizing stromatolites using various techniques. [7] [10] [11] In 2018, she published a study of 3.7 billion years old metasedimentary rocks in the Isua formation in Greenland. In this study, she and colleagues analyzed structures which were previously determined to be biogenic stromatolites.
Stromatolites were much more abundant in Precambrian times. While older, Archean fossil remains are presumed to be colonies of cyanobacteria, younger (that is, Proterozoic) fossils may be primordial forms of the eukaryote chlorophytes (that is, green algae). One genus of stromatolite very common in the geologic record is Collenia. The earliest ...
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