Oldest fossils of microbial structures yet: 3.7 billion years ago

Formation of our planet Earth originated ~4.54 billion years ago (BYA). Early fossil studies focused principally on digging up bones; hence, the creationist has argued that Earth is only 20,000 years old, or some today say only 6,004 years old. However, after radiocarbon dating of rocks in which fossils were discovered––began moving this “date at which life began” increasingly further back in time. Finding microbial structures embedded in rocks has moved this date from ~1.5 BYA back to 3.0 BYA and earlier.

Authors [see attached articles] now report evidence in the Isua supracrustal belt (ISB) of southwest Greenland for ancient life from a newly exposed outcrop of ~3.7-BYA meta-carbonate rocks in the ISB that contain 1– to 4-cm-high stromatolites––which are macroscopically layered structures produced by microbial communities. The ISB stromatolites grew in a shallow marine environment, as indicated by seawater-like rare-earth-element-plus yttrium-trace-element signatures of the meta-carbonates.

The ISB stromatolites predate, by 220 million years (Myr), the previous most convincing and generally accepted multidisciplinary evidence for oldest life remains found in the 3,480-Myr-old Dresser Formation of the Pilbara Craton in Australia. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2 sequestration by 3.7 BYA, which would be near the beginning of Earth’s sedimentary record. A sophistication of life by 3/7 BYA is consistent with genetic molecular clock studies placing life’s origin in the Hadean Eon (>4.0 BYA).

Nature  22 Sept 2o16; 537: 535–543  and  pp 500–501

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