Early trace of life from 3.95 Ga sedimentary rocks in Labrador, Canada
Early trace of life from 3.95 Ga sedimentary rocks in Labrador, Canada
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DOI：
10.1038/nature24019
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发表时间：
2017-09
期刊：
影响因子：
64.8
通讯作者：
T. Tashiro;A. Ishida;M. Hori;M. Igisu;M. Koike;Pauline Méjean;N. Takahata;Y. Sano;T. Komiya
中科院分区：
文献类型：
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作者：
T. Tashiro;A. Ishida;M. Hori;M. Igisu;M. Koike;Pauline Méjean;N. Takahata;Y. Sano;T. Komiya
太古宙岩石中的生命遗迹有可能阐明生命的起源。然而，从许多地形收集证据并不总是可能的，到目前为止，生物石墨只在3.7-3.8 Ga（10亿年前）的伊苏亚上地壳带被发现。本文研究了拉布拉多北部最古老的变质沉积岩中石墨（δ13Corg）和碳酸盐（δ13Ccarb）的总有机碳含量和碳同位素值。有些泥质岩石δ 13corg值较低，为−28.2，与较年轻岩石的最低值相当。石墨的结晶温度与寄主岩石的变质温度之间的一致性表明石墨不是来自后来的污染。δ 13corgvalue与变质等级的相关性较好，表明δ 13corgvalue的变化是变质作用的结果，变质前值低于最小值。我们认为δ 13carband δ13Corgvalues之间的大分馏值高达25‰，表明存在最古老的大于3.95 Ga的生物证据。生物石墨的发现使生物材料本身的地球化学研究成为可能，并将为了解地球上以及其他行星上的早期生命提供洞见。
The vestiges of life in Eoarchean rocks have the potential to elucidate the origin of life. However, gathering evidence from many terrains is not always possible,,, and biogenic graphite has thus far been found only in the 3.7–3.8 Ga (gigayears ago) Isua supracrustal belt,,,. Here we present the total organic carbon contents and carbon isotope values of graphite (δ13Corg) and carbonate (δ13Ccarb) in the oldest metasedimentary rocks from northern Labrador,. Some pelitic rocks have low δ13Corgvalues of −28.2, comparable to the lowest value in younger rocks. The consistency between crystallization temperatures of the graphite and metamorphic temperature of the host rocks establishes that the graphite does not originate from later contamination. A clear correlation between the δ13Corgvalues and metamorphic grade indicates that variations in the δ13Corgvalues are due to metamorphism, and that the pre-metamorphic value was lower than the minimum value. We concluded that the large fractionation between the δ13Ccarband δ13Corgvalues, up to 25‰, indicates the oldest evidence of organisms greater than 3.95 Ga. The discovery of the biogenic graphite enables geochemical study of the biogenic materials themselves, and will provide insight into early life not only on Earth but also on other planets.