Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon

Evidence of life on Earth is manifestly preserved in the rock record. However, the microfossil record only extends to similar to 3.5 billion years (Ga), the chemofossil record arguably to similar to 3.8 Ga, and the rock record to 4.0 Ga. Detrital zircons from Jack Hills, Western Australia range in age up to nearly 4.4 Ga. From a population of over 10,000 Jack Hills zircons, we identified one >3.8-Ga zircon that contains primary graphite inclusions. Here, we report carbon isotopic measurements on these inclusions in a concordant, 4.10 +/- 0.01-Ga zircon. We interpret these inclusions as primary due to their enclosure in a crack-free host as shown by transmission X-ray microscopy and their crystal habit. Their delta C-13(PDB) of -24 +/- 5% is consistent with a biogenic origin and may be evidence that a terrestrial biosphere had emerged by 4.1 Ga, or similar to 300 My earlier than has been previously proposed.