Chemostratigraphic insights on the evolution of surface environments and life over Earth's history

摘要自从早在41亿年前（Ga）地球上出现微生物生命以来，其进化与地球表面环境的进化直接相关。这种耦合演化是控制微量元素循环的地质和生物过程的综合结果。微生物谱系需要许多微量元素作为代谢活动所必需的微量营养素或作为酶中的组分。因此，古海洋沉积记录中微量元素丰度的变化可能与生物进化有关。铁的形成，铁和二氧化硅丰富的化学沉积岩，沉淀在太古代（4.0至2.5 Ga）和古元古代（2.5至1.6 Ga）的海洋，已被广泛用于重建微量元素丰度。这些是特别重要的记录，因为大部分铁形成沉积发生在大氧化事件（2.48至2.32 Ga）的直接导致和之后;表面环境中氧气的第一次永久性上升和基本的生物转变。然而，到目前为止，微量元素记录和太古代古元古代铁地层的化学地层剖面已主要建造在粗采样分辨率和推断古海水成分已从经验模型的微量元素分区前体矿物相。这些因素阻碍了确定环境或生物控制，驱动短期微量元素的变化，并导致对比古老的海水成分的估计。消除这种不确定性对我的研究计划的长期目标至关重要：更深入地了解地球历史上海洋地球化学和生物演化的耦合。因此，在这个NSERC发现补助金提案中，我概述了三个短期目标，旨在提高我们对古海洋地球化学条件和古海洋环境中微量元素循环控制的理解。目标1和2将产生新的化学地层学记录，包括一个燧石记录，跨越3.8 Ga的地球历史和高分辨率的记录，从2.5 Ga铁地层沉积接近大氧化事件。这些新的记录将产生的微量元素的可用性，这可以与现有的记录，并在机制，导致几十年到千年尺度的微量元素的变化，在全球氧合增加的约束。目标3将使用这些记录与铁的形成，铁的氢氧化物和无定形二氧化硅的前体沉积物的接地表面络合模型，以阐明古海水的组成的强大的估计。这些项目旨在支持我的长期目标，即限制生命和地球表面环境在过去4Ga中的协同进化。

SUMMARY Since the appearance of microbial life on Earth, as early as 4.1 billion years ago (Ga), its evolution has been tied directly to that of Earth's surface environments. This coupled evolution is the combined result of geological and biological processes that control trace element cycling. A number of trace elements are required by microbial lineages as micronutrients necessary for metabolic activity or as components in enzymes. Variations in trace element abundances in the ancient marine sedimentary record may therefore be tied to biological evolution. Iron formations, iron- and silica-rich chemical sedimentary rocks that precipitated in the Archean (4.0 to 2.5 Ga) and Paleoproterozoic (2.5 to 1.6 Ga) oceans, have been used extensively to reconstruct trace element abundances. These are especially important records, as the bulk of iron formation deposition occurs in the immediate lead up, and aftermath, of the Great Oxidation Event (2.48 to 2.32 Ga); the first permanent rise of oxygen in surface environments and a fundamental biological transition. To date, however, trace element records and chemostratigraphic profiles for Archean to Paleoproterozoic iron formations have been primarily constructed at coarse sampling resolutions and inferences regarding ancient seawater composition have been drawn from empirical models of trace element partitioning to precursor mineral phases. These factors have hindered the identification of environmental or biological controls that drive short-term trace element variability and have led to contrasting estimates for ancient seawater composition. Reconciling such uncertainties is critical to the long-term objective of my research programme: gaining a more robust understanding of coupled marine geochemical and biological evolution over Earth's history. Accordingly, in this NSERC Discovery Grant proposal, I have outlined three short-term objectives that seek to improve our understanding of paleomarine geochemical conditions and the controls on trace element cycling in ancient marine settings. Objectives 1 and 2 will generate new chemostratigraphic records including a chert record that spans 3.8 Ga of Earth's history and high-resolution records from 2.5 Ga iron formations deposited close to the Great Oxidation Event. These novel records will generate insights into trace element availability, which can be integrated with existing records, and constraints on the mechanisms that led to decadal to millennial scale trace element variability during increasing global oxygenation. Objective 3 will use these records alongside thermodynamically grounded surface complexation models for the precursor sediments to iron formations, iron oxyhydroxides and amorphous silica, to elucidate robust estimates for the composition of ancient seawater. These projects are designed to support my long-term goal of constraining how life and Earth's surface environments have evolved in tandem over the last 4 Ga.