Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA.
DSI-NRF Centre of Excellence for Integrated Mineral and Energy Resource Analysis, Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa.
Nat Commun. 2023 Jan 17;14(1):279. doi: 10.1038/s41467-023-35820-w.
Understanding the timing and trajectory of atmospheric oxygenation remains fundamental to deciphering its causes and consequences. Given its origin in oxygen-free photochemistry, mass-independent sulfur isotope fractionation (S-MIF) is widely accepted as a geochemical fingerprint of an anoxic atmosphere. Nevertheless, S-MIF recycling through oxidative sulfide weathering-commonly termed the crustal memory effect (CME)-potentially decouples the multiple sulfur isotope (MSI) record from coeval atmospheric chemistry. Herein, however, after accounting for unrecognised temporal and spatial biases within the Archaean-early-Palaeoproterozoic MSI record, we demonstrate that the global expression of the CME is barely resolvable; thereby validating S-MIF as a tracer of contemporaneous atmospheric chemistry during Earth's incipient oxygenation. Next, utilising statistical approaches, supported by new MSI data, we show that the reconciliation of adjacent, yet seemingly discrepant, South African MSI records requires that the rare instances of post-2.3-billion-year-old S-MIF are stratigraphically restricted. Accepting others' primary photochemical interpretation, our approach demands that these implied atmospheric dynamics were ephemeral, operating on sub-hundred-thousand-year timescales. Importantly, these apparent atmospheric relapses were fundamentally different from older putative oxygenation episodes, implicating an intermediate, and potentially uniquely feedback-sensitive, Earth system state in the wake of the Great Oxidation Event.
了解大气氧合作用的时间和轨迹仍然是破解其原因和后果的基础。鉴于其起源于无氧光化学，质量独立的硫同位素分馏（S-MIF）被广泛认为是缺氧大气的地球化学指纹。然而，通过氧化硫化物风化的 S-MIF 循环——通常称为地壳记忆效应（CME）——可能会使多个硫同位素（MSI）记录与同期大气化学脱钩。然而，在此之后，我们在考虑了太古宙-早期古元古代 MSI 记录中未被识别的时间和空间偏差之后，证明了 CME 的全球表达几乎无法分辨；从而验证了 S-MIF 是地球初始氧合作用期间同期大气化学的示踪剂。接下来，我们利用统计方法，并辅以新的 MSI 数据，表明协调相邻的、看似不一致的南非 MSI 记录需要将罕见的 23 亿年后的 S-MIF 事件在时间上进行限制。接受其他人的原始光化学解释，我们的方法要求这些隐含的大气动力学是短暂的，作用于数十万年内的时间尺度上。重要的是，这些明显的大气回退与更古老的潜在氧合作用事件根本不同，暗示了在大氧化事件之后，地球系统处于一种中间状态，可能具有独特的反馈敏感性。
