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Title:
Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon
Authors:
Bell, Elizabeth A.; Boehnke, Patrick; Harrison, T. Mark; Mao, Wendy L.
Affiliation:
AA(Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095), AB(Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095), AC(Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095), AD(School of Earth, Energy, and Environmental Sciences, Stanford University, Stanford, CA 94305)
Publication:
Proceedings of the National Academy of Sciences, Volume 112, Issue 47, 2015, pp.14518-14521
Publication Date:
11/2015
Origin:
CROSSREF; PNAS
DOI:
10.1073/pnas.1517557112
Bibliographic Code:
2015PNAS..11214518B

Abstract

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 delta13CPDB of -24 ± 50/00 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.
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