The rise of oxygenic photosynthesis arguably represents the most important evolutionary step in Earth history. Recent studies, however, suggest that Earth’s pre-oxidative atmosphere was also heavily influenced by biological feedbacks. Most notably, recent geochemical records propose the existence of a hydrocarbon haze which periodically formed in response to enhanced biospheric methane fluxes. Copper isotopes provide a potential proxy for biological methane cycling; Cu is a bioessential trace metal and a key element in the aerobic oxidation of methane to carbon dioxide (methanotrophy). In addition, Cu isotopes are fractionated during biological uptake. Here, we present a high-resolution Cu isotope record measured in a suite of shales and carbonates from core GKF01, through the ~2.6–2.5 Ga Campbellrand-Malmani carbonate platform. Our data show a 0.85‰ range in Cu isotope composition and a negative excursion that predates the onset of a haze event. We interpret this excursion as representing a period of enhanced aerobic methane oxidation before the onset of the Great Oxidation Event. This places valuable time constraints on the evolution of this metabolism and firmly establishing Cu isotopes as a biomarker in Late Archaean rocks.

有氧光合作用的兴起可以说是地球历史上最重要的进化步骤。然而，最近的研究表明，地球的氧化前大气也受到生物反馈的严重影响。最值得注意的是，最近的地球化学记录表明存在碳氢化合物雾霾，它周期性地形成，以响应生物圈甲烷通量的增加。铜同位素为生物甲烷循环提供了一个潜在的代表；Cu 是一种生物必需的微量金属，也是甲烷有氧氧化为二氧化碳（甲烷营养）的关键元素。此外，Cu 同位素在生物吸收过程中会被分馏。在这里，我们展示了通过 ~2.6-2.5 Ga Campbellrand-Malmani 碳酸盐平台在 GKF01 核心的一组页岩和碳酸盐岩中测量的高分辨率 Cu 同位素记录。我们的数据显示为 0。Cu同位素组成的范围为85‰，并且在雾霾事件开始之前出现负偏移。我们将这种偏移解释为代表大氧化事件开始前一段有氧甲烷氧化增强的时期。这为这种代谢的演变设置了宝贵的时间限制，并牢固地将铜同位素作为晚太古代岩石中的生物标志物。