Geologists report “compelling evidence” for microbial life in what is now eastern India at least 3.5 billion years ago. The study links two scientific tasks: age constraint using zircon crystals and biological interpretation using carbon chemical/isotopic evidence from a single ancient rock type in the Singhbhum Craton.
What happened (reported findings)
The study focuses on a carbon-bearing rock type called banded chert within the Singhbhum Craton, a very old and stable block of continental crust spanning parts of Jharkhand and Odisha. The research team argues that the rock contains signs consistent with biological carbon rather than later contamination.
Dating constraint: chert cannot be directly dated using the discussed method, so the study uses zircon crystals trapped within or associated with the chert.Natural clock method: U–Pb zircon geochronology (uranium-to-lead decay in zircon) provides zircon ages that cluster around 3,497 million years.Link between zircon and chert formation: some zircons are interpreted as volcanic ash deposited as the chert formed, supporting the zircon ages as a timing anchor for the chert.Biosignature carbon logic: carbon chemical and isotopic patterns are interpreted as matching carbon fixed by living cells rather than inorganic contamination.Organic matter logic: the study reports degraded organic matter characteristics rather than inorganic contamination.