Weathering, alteration and reconstructing Earth's oxygenation
Weathering, alteration and reconstructing Earth's oxygenation
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DOI：
10.1098/rsfs.2019.0140
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发表时间：
2020-06
期刊：
影响因子：
4.4
通讯作者：
N. Planavsky;L. Robbins;B. Kamber;R. Schoenberg
中科院分区：
文献类型：
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作者：
N. Planavsky;L. Robbins;B. Kamber;R. Schoenberg
解开游离氧水平在控制复杂生命辐射的时间和节奏方面所起的作用——如果有的话——是地球和生命科学中最基本的问题之一。准确地重建地球的氧化还原历史是解决这个问题的关键部分。在过去的几十年里，有大量的研究利用地球化学氧化还原代理来努力讲述地球氧合的故事。然而，许多这样的研究，即使是那些考虑相同的地球化学代理系统的研究，也导致了对氧化事件的时间和强度的相互矛盾的解释。对于相互矛盾的氧化还原重建，有两种可能的解释：(i)自由氧水平在时间和空间上都是难以置信的动态，或者（ii）作为一个群体，包括本文作者在内，我们经常研究受二次风化和蚀变（特别是二次氧化）影响的岩石，而忽略了解决这种蚀变对生成数据的影响。现在有多个案例研究记录了以前被忽视的次生蚀变，解决了有关氧化还原演化的一些相互冲突的限制。通过对一个大型页岩地球化学数据库的分析，我们发现，在露头岩心和钻孔岩心样品之间，铈（Ce）异常（一种常见的古氧化还原指标）存在显著差异。这种不一致为来自改变样本的地球化学数据经常在同行评议的文献中发表的观点提供了支持。作为个人和地球化学社区，我们大多数人都没有意识到这个问题有多普遍，但也有其他社区面临并应对这种质量控制危机带来的挑战的例子。进一步的证据表明，深时地球化学样品具有很高的蚀变潜力，并认识到这可能导致虚假的结果和古环境解释，表明样品存档，在可公开获取的集合中，需要成为发表新的古还原数据的先决条件。最后，地球化学界需要考虑如何实施额外的质量控制措施，以提高古还原世代理工作的保真度。
Deciphering the role—if any—that free oxygen levels played in controlling the timing and tempo of the radiation of complex life is one of the most fundamental questions in Earth and life sciences. Accurately reconstructing Earth's redox history is an essential part of tackling this question. Over the past few decades, there has been a proliferation of research employing geochemical redox proxies in an effort to tell the story of Earth's oxygenation. However, many of these studies, even those considering the same geochemical proxy systems, have led to conflicting interpretations of the timing and intensity of oxygenation events. There are two potential explanations for conflicting redox reconstructions: (i) that free oxygen levels were incredibly dynamic in both time and space or (ii) that collectively, as a community—including the authors of this article—we have frequently studied rocks affected by secondary weathering and alteration (particularly secondary oxidation) while neglecting to address the impact of this alteration on the generated data. There are now multiple case studies that have documented previously overlooked secondary alteration, resolving some of the conflicting constrains regarding redox evolution. Here, an analysis of a large shale geochemistry database reveals significant differences in cerium (Ce) anomalies, a common palaeoredox proxy, between outcrop and drill core samples. This inconsistency provides support for the idea that geochemical data from altered samples are frequently published in the peer-reviewed literature. As individuals and a geochemical community, most of us have been slow to appreciate how pervasive the problem is but there are examples of other communities that have faced and met the challenges raised by such quality control crises. Further evidence of the high potential for alteration of deep-time geochemical samples, and recognition of the manner in which this may lead to spurious results and palaeoenvironmental interpretations, indicate that sample archiving, in publicly accessible collections needs to become a prerequisite for publication of new palaeoredox data. Finally, the geochemical community need to think about ways to implement additional quality control measures to increase the fidelity of palaeoredox proxy work.