据研究人员介绍，古代岩石的有机碳含量提供了早期地球生物圈的基本记录。50多年来，太古宙（>2.5 Ga）泥岩有机质含量高这个问题，一直困扰着地质学家和进化生物学家，因为在O2升高之前，新生生物圈的生物初级生产力高几乎是不可能的。
该团队人员采取不同的方法来研究太古代富有机质泥岩的聚集速率，以解释这个明显的悖论。研究人员利用新发表的地层中灰岩的U-Pb锆石年龄，对McRae山页岩和Jeerinah组（澳大利亚Pilbara克拉通，2.68-2.48Ga）的三个剖面的沉积速率进行了评价。为了进行比较，研究人员还收集了来自可比沉积环境的显生宙（<500Ma）数据，并开发了一个理想化的模型，该模型考虑了沉积速率来预测岩石有机质含量。
结果发现，太古宙富有机质泥岩沉积速率极低（约1m/Ma），与显生宙富有机质泥岩沉积速率（10-100m/Ma）形成鲜明对比。模型显示，太古宙的初级生产力较显生宙低（比显生宙低约100倍），缺氧条件下增保存能力增强，有机碳含量主要受无机沉积物稀释的控制。因此，高有机碳含量通常被归因于高生产力，而不是反映了缓慢的积累，高保存和最小的无机稀释——与太古宙时期缓慢的碳循环节奏的地质证据相一致。
附：英文原文
Title: Reconciling Archean organic-rich mudrocks with low primary productivity before the Great Oxygenation Event
Author: Lotem, Noam, Rasmussen, Birger, Zi, Jian-Wei, Zeichner, Sarah S., Present, Theodore M., Bar-On, Yinon M., W. Fischer, Woodward
Issue&Volume: 2025-1-6
Abstract: The organic carbon content of ancient rocks provides a fundamental record of the biosphere on early Earth. For over 50 y, the high organic content of Archean (>2.5 Ga) mudrocks has puzzled geologists and evolutionary biologists, because high biological primary productivity was unexpected for the nascent biosphere before the rise of O2. Here, we took a different approach to resolve this apparent paradox, by studying the accumulation rates of Archean organic-rich mudrocks. We evaluated the sedimentation rates of three sections of the Mount McRae Shale and Jeerinah Formation (2.68 to 2.48 Ga, Pilbara Craton, Australia) with new and recently published U–Pb zircon ages from intraformational ash beds. For comparison, we compiled Phanerozoic (<500 Ma) data from comparable depositional settings and developed an idealized model that considers the sedimentation rates for predicting rock organic content. We found that organic-rich Archean mudrocks were deposited under exceptionally low sedimentation rates (~1 m/Ma), in sharp contrast to organic-rich rocks from the Phanerozoic Eon (10 to 100 m/Ma). Constrained by observations, model results indicated that the Archean data reflect low primary productivity (~100-fold lower than during the Phanerozoic) and enhanced preservation under anoxic conditions, with the principal control on organic carbon content provided by dilution with inorganic sediment. Thus, the high organic carbon content which is typically attributed to high productivity instead reflects slow accumulation, high preservation, and minimal inorganic dilution—reconciling the geological evidence with a slow carbon cycle cadence during Archean time.
DOI: 10.1073/pnas.2417673121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2417673121