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

早在41亿年前，地球上就出现了微生物，微生物的进化与地球表面环境直接相关。这种耦合演化是控制微量元素循环的地质和生物过程共同作用的结果。微生物谱系需要一些微量元素作为代谢活动所必需的微量营养素或作为酶的组成部分。因此，古代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。在太古宙（4.0 ~ 2.5 Ga）和古元古代（2.5 ~ 1.6 Ga）海洋中沉积的富铁和富硅化学沉积岩，已被广泛用于重建微量元素丰度。这些是特别重要的记录，因为大部分铁沉积发生在大氧化事件（2.48 - 2.32 Ga）之前和之后；地表环境中氧气的第一次永久上升和一个基本的生物转变。然而，迄今为止，太古宙至古元古代铁地层的微量元素记录和化学地层剖面主要是在粗采样分辨率下建立的，而关于古代海水成分的推断主要是根据微量元素分配到前驱矿物相的经验模型得出的。这些因素阻碍了对驱动短期微量元素变化的环境或生物控制的识别，并导致了对古代海水成分的对比估计。协调这些不确定性对我的研究计划的长期目标至关重要：对地球历史上海洋地球化学和生物的耦合进化有更有力的了解。因此，在这份NSERC发现资助提案中，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和目标2将生成新的化学地层记录，包括跨越3.8 Ga地球历史的燧石岩记录和靠近大氧化事件沉积的2.5 Ga铁地层的高分辨率记录。这些新记录将有助于了解微量元素的可用性，并将其与现有记录相结合，以及在全球氧合增加过程中导致年代际至千年尺度微量元素变化的机制。目标3将利用这些记录与铁地层、铁氧氢氧化物和无定形二氧化硅的前体沉积物的热力学表面络合模型一起，阐明对古代海水组成的可靠估计。这些项目的设计是为了支持我的长期目标，即限制生命和地球表面环境是如何在过去的4亿年里同步进化的。

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.