Dating the rise of atmospheric oxygen
Dating the rise of atmospheric oxygen
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DOI：
10.1038/nature02260
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发表时间：
2004-01-08
期刊：
影响因子：
64.8
通讯作者：
Beukes, NJ
中科院分区：
文献类型：
--
作者：
Bekker, A;Holland, HD;Beukes, NJ
一些地质和地球化学证据表明，在24.5亿年前（Gyr），大气中的氧气水平极低，到2.22 Gyr前已经达到相当高的水平。在这里，我们提出的证据表明，大气中氧气的上升已经发生了2.32 Gyr前。我们发现，同生黄铁矿是存在于2.32-Gyr-old Rooihoogte和Timeball山地层，南非的有机质丰富的页岩。该黄铁矿中硫的同位素组成范围很大，没有显示出质量无关分馏的证据，表明在这些单元的沉积过程中，大气中的氧含量很高（即大于现在大气中氧含量的10（-5）倍）。在Rooihoogte地层的底部存在着菱铁矿的圆形鹅卵石，在上Timeball Hill地层中存在着由赤铁矿豆石和赭石组成的广泛而厚的铁矿石层，这表明在Rooihoogte和Timeball Hill地层的沉积过程中，大气中的氧气可能首次显著上升。这些单位之间的沉积可能是第二次和第三次古元古代冰川事件。
Several lines of geological and geochemical evidence indicate that the level of atmospheric oxygen was extremely low before 2.45 billion years (Gyr) ago, and that it had reached considerable levels by 2.22 Gyr ago. Here we present evidence that the rise of atmospheric oxygen had occurred by 2.32 Gyr ago. We found that syngenetic pyrite is present in organic-rich shales of the 2.32-Gyr-old Rooihoogte and Timeball Hill formations, South Africa. The range of the isotopic composition of sulphur in this pyrite is large and shows no evidence of mass-independent fractionation, indicating that atmospheric oxygen was present at significant levels ( that is, greater than 10(-5) times that of the present atmospheric level) during the deposition of these units. The presence of rounded pebbles of sideritic iron formation at the base of the Rooihoogte Formation and an extensive and thick ironstone layer consisting of haematitic pisolites and oolites in the upper Timeball Hill Formation indicate that atmospheric oxygen rose significantly, perhaps for the first time, during the deposition of the Rooihoogte and Timeball Hill formations. These units were deposited between what are probably the second and third of the three Palaeoproterozoic glacial events.