Bekker A, Holland H D, Wang P-L, Rumble D, Stein H J, Hannah J L, Coetzee L L, Beukes N J
Department of Earth and Planetary Sciences, 20 Oxford Street, Harvard University, Cambridge, Massachusetts 02138, USA.
Nature. 2004 Jan 8;427(6970):117-20. doi: 10.1038/nature02260.
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 oölites 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.
多条地质和地球化学证据表明，在24.5亿年前之前，大气中的氧气水平极低，而到22.2亿年前时已达到相当高的水平。在此我们提供证据表明，大气氧气含量的上升在23.2亿年前就已发生。我们发现，在南非23.2亿年前的鲁伊胡格特和时球山地层富含有机物质的页岩中存在同生黄铁矿。这种黄铁矿中硫的同位素组成范围很大，且没有显示出质量无关分馏的证据，这表明在这些地层沉积期间，大气中的氧气含量已达到显著水平（即大于当前大气水平的10^(-5)倍）。鲁伊胡格特地层底部菱铁矿层的圆形卵石以及时球山顶部地层中由赤铁矿豆石和鲕粒组成的广泛且厚的铁矿层表明，在鲁伊胡格特和时球山地层沉积期间，大气中的氧气含量显著上升，或许这是首次出现这种情况。这些地层沉积于古元古代三次冰川事件中可能的第二次和第三次之间。
