2015/10/19 by Elizabeth A. Bell, P. Boehnke, T. Mark Harrison +1 · 12 citations
Earth and Planetary Sciences · #Geological and Geochemical Analysis #Paleontology and Stratigraphy of Fossils #Geochemistry and Elemental Analysis
paper · pdf · doi:10.1073/pnas.1517557112
openalex publication_date 2015/10/19 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/02
Evidence of life on Earth is manifestly preserved in the rock record. However, the microfossil record only extends to ∼ 3.5 billion years (Ga), the chemofossil record arguably 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 δ(13)CPDB of -24 ± 5‰ is consistent with a biogenic origin and may be evidence that a terrestrial biosphere had emerged by 4.1 Ga, or ∼ 300 My earlier than has been previously proposed.