Direct dating of 3.5 Ga biogenic carbon in a microbial mat remnant, Singhbhum Craton, India.
basic_science · Level V
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- Record sourced from PubMed, PMID 42607217.
- Also identified by DOI 10.1073/pnas.2617912123.
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Abstract
Zircons interpreted to be of syn-volcanic origin recovered from the lower greenschist "black and white banded" Bhitardari chert, Eastern Iron Ore greenstone belt, Singhbhum craton, India, yield a <sup>207</sup>Pb/<sup>206</sup>Pb zircon age of 3497 ± 5 Ma (<i>n</i> = 4; MSWD = 1.2). This chert contains abundant carbonaceous matter (CM) that occurs in two textural modes: 1) ultrafine laminae distributed within the matrix and 2) graphite flakes in late quartz veins. Bulk δ<sup>13</sup>C<sub>CM</sub> of both modes in the Bhitardari chert yield a value of -30.9‰, which we interpret as reflecting a biogenic origin. This represents the documentation of a directly dated, CM-bearing, Paleoarchean rock with δ<sup>13</sup>C<sub>CM</sub> diagnostic of biologic activity. The observed isotopic compositions are consistent with the rise of relatively sophisticated metabolic mechanisms (e.g., Calvin cycle) by 3.5 Ga.