Tracking the emergence oxygenic photosynthesis with metal isotopes: A case study from the Pongola Supergroup

诺亚·普拉纳夫斯基博士被授予美国国家科学基金会地球科学博士后奖学金，以查明氧气光合作用的出现，由加州理工学院主办。随着地球表面的逐渐氧化，海洋的化学成分发生了巨大的变化。毫无疑问，地球渐进氧化过程中最重要的事件是含氧光合作用的发展，它只依赖于无处不在的二氧化碳和水分子，并使生物能够开拓地球上阳光照射到的每一个地方。这种代谢的成功反映在其废物——分子氧的丰度上。尽管在过去的50年里进行了详细的研究，但关于含氧光合作用进化的时间仍然存在激烈的争论，普遍的估计跨越了10亿年。这项提议的工作将使用新兴的重金属同位素系统来追踪含氧光合作用的兴起。在这项研究中，将利用钼（Mo）和铬（Cr）同位素系统的独特性质来阐明地球早期海洋中锰（Mn）的循环。研究锰氧化是必要的，因为其他氧化还原转化（例如，铁氧化）可能发生在无氧条件下。这项研究将集中在32亿到25亿年前沉积的岩石上，跨越了生物氧气生产最典型的预测进化的时间范围。此外，普拉纳夫斯基博士将开展教育活动，让本科生参与调查。精确定位氧气产生的开始对于理解生物进化的节奏至关重要，并将为一般的行星进化提供重要的见解。此外，考虑到产氧光合作用在控制地球氧化还原状态和碳循环中的重要性，解决太古宙中期是否有氧气产生的问题将成为理解地球早期所有主要生物地球化学循环的基础。

Dr. Noah Planavsky has been awarded an NSF Earth Sciences Postdoctoral Fellowship in order to pinpoint the emergence of oxygenic photosynthesis, hosted by the California Institute of Technology. The chemical composition of the ocean has changed dramatically with the gradual oxidation of the Earth's surface. Undoubtedly the single most important event in Earth's progressive oxygenation was the development of oxygenic photosynthesis, which relies only on the ubiquitous molecules carbon dioxide and water, and allowed organisms to pioneer essentially every part of the Earth reached by sunlight. The success of this metabolism is reflected in the abundance of its waste product - molecular oxygen. Despite detailed investigations over the past 50 years, there is still intense debate about the timing of the evolution of oxygenic photosynthesis, with common estimates spanning over one billion years. The proposed work will use emerging heavy metal isotope systems to track the rise of oxygenic photosynthesis. In this study, unique properties of the molybdenum (Mo) and chromium (Cr) isotope systems will be utilized to shed light on manganese (Mn) cycling in the Earth's early oceans. Investigation of Mn oxidation is essential since other redox transformations (e.g., iron oxidation) may take place in oxygen-free conditions. The study will focus on rocks deposited from 3.2 to 2.5 billion years ago, spanning the range of time during which biological oxygen production is most typically predicted to have evolved. In addition, Dr. Planavsky will carry out educational activities by engaging undergraduate students in the investigation. Pinpointing the onset of oxygen production is central to understanding the tempo of biological evolution, and will provide important insights into planetary evolution in general. Further, given the importance of oxygenic photosynthesizers in controlling Earth's redox state and the carbon cycle, addressing the question of whether or not there was oxygen production in the mid-Archean will serve as a grounding point for understanding all major biogeochemical cycles on the early Earth.