Australia: The Land Where Time Began

A biography of the Australian continent 

Jack Hills - Light Carbon Reservoir Recorded in Zircon-Hosted Diamond

A unique opportunity to investigate the Earth’s oldest known carbon reservoir has been provided by a recent discovery of diamond-graphite inclusions in the oldest known zircon grains, dating to up to 4,252 Ma, from the metasediments of Jack Hills in Western Australia. In this paper Nemchin et al. report the results of ion probe analyses of these diamond-graphite inclusions. The δ¹³C_PDB values observed, expressed in the PeeDee Belemnite standard, ranging from -5/ml to -58/ml with a median of -31/ml. This extends beyond mantle values typically of around -6/ml to values that are observed in metamorphic and some eclogitic diamonds that have been interpreted to reflect deep subduction of low δ¹³C_PDB biogenic surface carbon. Inorganic chemical reactions (2) may also produce low δ¹³C_PDB values, which therefore means they are not unambiguous evidence of life on Earth as early as 4,250 Ma. Their results nevertheless suggest that a low δ¹³C_PDB reservoir may have existed on the early Earth in the deep past.

Sources & Further reading

1. Nemchin, A. A., M. J. Whitehouse, M. Menneken, T. Geisler, R. T. Pidgeon and S. A. Wilde (2008). "A light carbon reservoir recorded in zircon-hosted diamond from the Jack Hills." Nature 454(7200): 92-95.