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 ∼ 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.
Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095; ebell21@ucla.edu tmark.harrison@gmail.com.
Elizabeth A
EA
Bell
Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095;
Patrick
http://orcid.org/0000-0002-6332-5086
P
Boehnke
Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095; ebell21@ucla.edu tmark.harrison@gmail.com.
T Mark
TM
Harrison
School of Earth, Energy, and Environmental Sciences, Stanford University, Stanford, CA 94305.
Wendy L
WL
Mao
D002244:Carbon / Q000032:analysis*; D018534:Earth, Planet; D017640:Silicates / Q000032:analysis*; D015040:Zirconium / Q000032:analysis*
D017640:Silicates; C003784:zircon; D002244:Carbon; D015040:Zirconium
Hadean; carbon isotopes; early Earth; origin of life; zircon