Potentially biogenic carbon preserved in a 4.1 billion year old zircon


Tuesday, February 16 2016 - 12:00 pm, PST
Elizabeth Bell

Although our planet is approximately 4.5 billion years old (Ga), Earth’s fossil record extends only to 3.5 Ga, the chemofossil record arguably to 3.8 Ga, and the rock record to 4.0 Ga.  However, detrital zircons from Jack Hills, Western Australia range in age up to nearly 4.4 Ga.  From a population of over 10,000 zircons from this locality, we identified one 4.10 Ga zircon that contains primary graphite inclusions in a crack-free region, and report carbon isotopic measurements on the graphite.  Evidence for carbon cycling or biologic activity can be derived from carbon isotopic studies, since a high ratio of 12C/13C is characteristic of biogenic carbon.  The 12C-rich isotopic signature of these graphite inclusions is consistent with a biogenic origin and may be evidence that a terrestrial biosphere had emerged by 4.1 Ga, or ~300 million years earlier than has been previously proposed.


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