The emergence of oxygenic photosynthesis through the lens of carbonate diagenesis

碳酸盐岩成岩作用下含氧光合作用的出现

• 批准号: RGPIN-2022-03912
• 负责人: Ahm, AnneSofie
• 金额: $ 2.19万
• 依托单位: University of Victoria
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=750963
• 关键词: emergence; oxygenic; photosynthesis; through; lens

The most important evolutionary innovation in Earth history was the emergence of oxygenic photosynthesis. The evolution of this microbial metabolism eventually drove the rise of oxygen in the atmosphere, fundamentally changing all biogeochemical cycles, and setting the stage for the subsequent evolution of multi-cellular life. However, the timing, causes, and consequences of this evolutionary singularity are largely unresolved. Currently, theories on the origin of oxygenic photosynthesis are divided. While some studies favor an early origin of oxygenic photosynthesis, ~600 million years prior to the rise of oxygen in the atmosphere, others have argued that oxygenic photosynthesis arose just prior to the Great Oxidation Event (~2.3-3.4 billion years ago). This controversy is intrinsically linked to the complications associated with interpreting geochemical data from billion-year-old Archean rocks. The history of oxygen on Earth has in part been reconstructed using geochemical data from ancient sediments, such carbonates. These chemical sediments are composed of cations (e.g., Ca2+, Mg2+) and carbonate ions whose composition, at least initially, reflects the chemical and isotopic composition of contemporaneous seawater. However, one of the main limitations in using this geochemical archive is the susceptibility of carbonate sediments to diagenesis, the process where unlithified sediments are transformed into the rocks we can study today. For billion-year-old carbonates diagenetic alteration is the rule rather than the exception and extensive recrystallization has modified the geochemical signals that are preserved in the rock record. These post-depositional processes are major obstacles for our ability to accurately infer oxygen levels before the GOE. In contrast to common attempts of trying to avoid diagenesis, the research program outlined in this proposal seeks to extract the primary chemical information from ancient carbonate sediments by mapping out and better understanding the diagenetic processes. By combining calcium isotope measurements, synchrotron X-ray analyses of Mn and Fe minerals, and numerical diagenetic models, it is possible to constrain the diagenetic history of carbonates. When paring these techniques with textural observations, it is possible to `see through' diagenesis and more accurately reconstruct past seawater chemistry. The pursuit of reconstructing ancient environments through the lens of carbonate diagenesis is not only relevant to Archean studies, but is pertinent to all studies using the geochemistry of carbonates as proxies for ancient environmental conditions. Consequently, this framework is both highly original and likely to lead to ground-breaking advances in our understanding of the emergence of oxygenic photosynthesis and the evolutionary history of life throughout Earth history.

地球历史上最重要的进化创新是氧气光合作用的出现。这种微生物代谢的演变最终使氧气在大气中的兴起，从根本上改变了所有生物地球化学周期，并为随后的多细胞寿命的演变奠定了基础。但是，这种进化奇点的时机，原因和后果在很大程度上尚未解决。当前，关于氧光合物的起源的理论被划分了。尽管一些研究有利于氧光合作用的早期起源，但在大气中氧气兴起之前约有6亿年，但另一些研究则认为，在发生大氧化事件之前（约2.3-34亿年前）出现了氧合光合作用。这一争议与解释数十亿年历史的Archean Rocks的地球化学数据相关的并发症本质上有关。 地球上的氧史部分是使用古代沉积物（此类碳酸盐）的地球化学数据重建的。这些化学沉积物由阳离子（例如Ca2+，Mg2+）和碳酸盐离子组成，其组成至少最初反映了同时海水的化学和同位素组成。然而，使用这种地球化学档案的主要局限性之一是碳酸盐沉积物对成岩作用的敏感性，这一过程将无形的沉积物转化为我们今天可以研究的岩石。对于十亿年历史的碳酸盐改变是规则而不是例外，并且广泛的重结晶修改了保留在岩石记录中的地球化学信号。这些沉积后过程是我们在GOE之前准确推断氧气水平的能力的主要障碍。 与试图避免成岩作用的常见尝试相反，该提案中概述的研究计划旨在通过绘制和更好地理解成生岩过程来从古代碳酸盐沉积物中提取主要的化学信息。通过结合同位素测量，MN和FE矿物质的同步子X射线分析以及数值成岩模型，可以限制碳酸盐的成岩成分病史。当通过纹理观察削减这些技术时，可以“看到”成岩作用，并更准确地重建过去的海水化学。 追求通过碳酸盐成岩的镜头重建古老环境不仅与大将研究有关，而且与所有使用碳酸盐地球化学作为古代环境条件的代理有关的所有研究。因此，这个框架既是高度原始的，又可能导致我们对氧合光合作用的出现以及整个地球历史的生命的进化历史的突破性进步。