Nano-Science Center, Department of Chemistry, University of Copenhagen, Copenhagen 2100, Denmark.
Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, Kongens Lyngby 2800, Denmark.
Nature. 2017 Aug 3;548(7665):78-81. doi: 10.1038/nature23261. Epub 2017 Jul 24.
Metasedimentary rocks from Isua, West Greenland (over 3,700 million years old) contain C-depleted carbonaceous compounds, with isotopic ratios that are compatible with a biogenic origin. Metamorphic garnet crystals in these rocks contain trails of carbonaceous inclusions that are contiguous with carbon-rich sedimentary beds in the host rock, where carbon is fully graphitized. Previous studies have not been able to document other elements of life (mainly hydrogen, oxygen, nitrogen and phosphorus) structurally bound to this carbonaceous material. Here we study carbonaceous inclusions armoured within garnet porphyroblasts, by in situ infrared absorption on approximately 10 m domains within these inclusions. We show that the absorption spectra are consistent with carbon bonded to nitrogen and oxygen, and probably also to phosphate. The levels of C-H or O-H bonds were found to be low. These results are consistent with biogenic organic material isolated for billions of years and thermally matured at temperatures of around 500 °C. They therefore provide spatial characterization for potentially the oldest biogenic carbon relics in Earth's geological record. The preservation of Eoarchean organic residues within sedimentary material corroborates earlier claims for the biogenic origins of carbon in Isua metasediments.
来自格陵兰岛西部伊苏瓦的变质沉积岩（超过 37 亿年）含有碳亏损的含碳化合物，其同位素比值与生物起源相容。这些岩石中的变质石榴石晶体含有含碳包裹体的轨迹，这些包裹体与母体岩石中富碳的沉积层连续，其中碳完全石墨化。以前的研究未能记录到与这种含碳物质结构结合的生命的其他元素（主要是氢、氧、氮和磷）。在这里，我们通过对这些包裹体中约 10μm 域的原位红外吸收来研究包裹在石榴石斑晶中的含碳包裹体。我们表明，吸收光谱与与氮和氧结合的碳一致，可能还与磷酸盐结合的碳一致。发现 C-H 或 O-H 键的水平较低。这些结果与数十亿年来隔离并在约 500°C 的温度下热成熟的生物有机材料一致。因此，它们为地球地质记录中可能最古老的生物碳遗迹提供了空间特征。在沉积物质中保存的太古代有机残留物证实了伊苏瓦变质沉积物中碳的生物起源的早期说法。
