Direct dating of 3.5 Ga biogenic carbon in a microbial mat remnant, Singhbhum Craton, India.

Authors

Trisrota Chaudhuri, T Mark Harrison, Elizabeth A Bell, Mark Van Zuilen, Léna Thomas, Nouf Al Alawi, Rajat Mazumder, Stefan V Lalonde

Published in

Proceedings of the National Academy of Sciences of the United States of America. Volume 123. Issue 34. Pages e2617912123. Aug 25, 2026. Epub Aug 17, 2026.

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 ²⁰⁷Pb/²⁰⁶Pb 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 δ¹³C_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 δ¹³C_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.

PMID:
42607217
Bibliographic data and abstract were imported from PubMed on 18 Aug 2026.

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