Geochemical analysis reveals 3.5-billion-year-old biogenic carbon signatures in Paleoarchean chert, indicating that sophisticated metabolic pathways evolved exceptionally early in Earth's history.
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 207 Pb/ 206 Pb zircon age of 3497 ± 5 Ma ( n = 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 13 C CM 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 13 C CM 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.
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Chaudhuri et al. (2026) studied this question.
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