Letter

Nature 454, 92-95 (3 July 2008) | doi:10.1038/nature07102; Received 11 September 2007; Accepted 14 May 2008

A light carbon reservoir recorded in zircon-hosted diamond from the Jack Hills

Alexander A. Nemchin1, Martin J. Whitehouse2, Martina Menneken3, Thorsten Geisler3, Robert T. Pidgeon1 & Simon A. Wilde1

  1. Department of Applied Geology, Western Australian School of Mines, Curtin University of Technology, Bentley, Western Australia 6102, Australia
  2. Laboratory for Isotope Geology, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden
  3. Institut für Mineralogie, Westfälische Wilhelms-Universität, Corrensstrasse 24, 48149 Münster, Germany

Correspondence to: Alexander A. Nemchin1 Correspondence and requests for materials should be addressed to A.A.N. (Email: nemchina@kalg.curtin.edu.au).

The recent discovery of diamond–graphite inclusions in the Earth's oldest zircon grains (formed up to 4,252 Myr ago) from the Jack Hills metasediments in Western Australia1 provides a unique opportunity to investigate Earth's earliest known carbon reservoir. Here we report ion microprobe analyses of the carbon isotope composition of these diamond–graphite inclusions. The observed delta13CPDB values (expressed using the PeeDee Belemnite standard) range between -5 per mil and -58 per mil with a median of -31 per mil. This extends beyond typical mantle values of around -6 per mil to values observed in metamorphic and some eclogitic diamonds that are interpreted to reflect deep subduction of low-delta13CPDB biogenic surface carbon. Low delta13CPDB values may also be produced by inorganic chemical reactions2, and therefore are not unambiguous evidence for life on Earth as early as 4,250 Myr ago. Regardless, our results suggest that a low-delta13CPDB reservoir may have existed on the early Earth.

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