Nemchin Alexander A, Whitehouse Martin J, Menneken Martina, Geisler Thorsten, Pidgeon Robert T, Wilde Simon A
Department of Applied Geology, Western Australian School of Mines, Curtin University of Technology, Bentley, Western Australia 6102, Australia.
Nature. 2008 Jul 3;454(7200):92-5. doi: 10.1038/nature07102.
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 Australia 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 delta(13)C(PDB) 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-delta(13)C(PDB) biogenic surface carbon. Low delta(13)C(PDB) values may also be produced by inorganic chemical reactions, and therefore are not unambiguous evidence for life on Earth as early as 4,250 Myr ago. Regardless, our results suggest that a low-delta(13)C(PDB) reservoir may have existed on the early Earth.
最近在西澳大利亚杰克山变质沉积物中发现了地球最古老锆石颗粒（形成于42.52亿年前）中的金刚石-石墨包裹体，这为研究地球已知最早的碳储库提供了独特的机会。在此，我们报告了这些金刚石-石墨包裹体碳同位素组成的离子微探针分析结果。观察到的δ(13)C(PDB)值（使用皮迪鲕粒灰岩标准表示）在-5‰至-58‰之间，中位数为-31‰。这超出了典型地幔值约-6‰，延伸到变质和一些榴辉岩金刚石中观察到的值，这些值被解释为反映了低δ(13)C(PDB)生物源表层碳的深度俯冲。低δ(13)C(PDB)值也可能由无机化学反应产生，因此并非42.5亿年前地球上存在生命的确凿证据。尽管如此，我们的结果表明早期地球可能存在一个低δ(13)C(PDB)储库。
