Reconciling biological and geochemical perspectives on the production of oxygen on early Earth

大氧化事件（GOE）是指地球大气中的游离O2水平从零上升到今天的10-5倍以上的时期。然而，在太古代浅水环境和陆上地壳中发现了早期局部氧化的证据，即所谓的“喷流”。当考虑到最近的基因组系统发育研究表明，蓝藻，唯一能够进行氧化光合作用的细菌，出现至少2.7 Ga，而水的氧化分解进化得更早，问题是为什么地球大气的氧化需要另外0.3 Ga。一种假设是，生物必需营养素的限制，如硝酸盐，磷酸盐和微量金属，意味着蓝藻无法茁壮成长。另一种假说认为，局部氧化的陆壳矿物吸附的O2释放的蓝藻。本项目通过利用海洋和淡水固氮蓝藻的液体培养物来解决这些假设，以确定在还原，厌氧太古代大气中二氧化碳浓度升高的情况下光合作用和生物固氮的速率。根据这是试验，以评估营养限制的影响，蓝藻初级生产在太古代。通过在地面岩石的固体基质上生成假垫，我们将能够确定在矿物：微生物界面上发生的与O2浓度以及pH和氧化还原变化有关的确切相互作用。将来自个人的数据相结合，同步液体培养物与从pseudomats获得的数据，将提供对古代蓝藻的现代后代的生长和生理反应的洞察，在个体生物体的水平和生态群落的反应垫。实验获得的数据将进行比较的总氮和微量元素含量确定的有机丰富层保存的微生物垫和叠层石从海洋和非海洋环境。这是第一项研究，探讨潜在的营养限制蓝藻在太古代晚期，以及他们的能力，通过风化的矿物基质，导致了GOE的来源必需的微量元素。

The Great Oxygenation Event (GOE) is the period during which the level of free O2 in the Earth’s atmosphere rose from zero to above ~ 10-5 times that of today. However, evidence of early pockets of localised oxygenation, the so called "whiffs", are being found in Archeal shallow water environments and subaerial crust. When considered together with recent genomic phylogenetic investigations indicating that cyanobacteria, the only bacteria able to conduct oxidative photosynthesis, arose at least 2.7 Ga, and that the oxidative splitting of water evolved even earlier, the question arises as to why it took another 0.3 Ga for the oxygenation of the Earth’s atmosphere. One hypothesis is that limitation of bioessential nutrients such as nitrates, phosphates and trace metals, meant that the cyanobacteria were unable to thrive. Another hypothesis suggests that localised oxidation of subaerial crustal minerals adsorbed O2 released by cyanobacteria. This project addresses these hypotheses by utilising liquid cultures of both marine and freshwater nitrogen fixing cyanobacteria to determine the rates of photosynthesis and biological nitrogen fixation under a reducing, anaerobic Archean atmosphere with elevated CO2. Pursuant to this are trials to assess the effects of nutrient limitation on cyanobacterial primary production during the Archean. By generating pseudomats on a solid matrix of ground rocks, we will be able to determine the exact interactions occurring at the mineral: microbe interface with respect to O2 concentrations as well as pH and Redox changes. Combining data from the individual, synchronised liquid cultures with that obtained from pseudomats, will provide insight into the growth and physiological responses of modern-day descendants of ancient cyanobacteria at the level of the individual organism AND the ecological community response in mats. The experimentally obtained data will be compared to the total N and trace element content determined for organic rich layers of preserved microbial mats and stromatolites from marine and non-marine settings. This is the first study to investigate the potential nutrient limitations on cyanobacteria during the late Archean, and their ability to source essential trace elements via weathering of their mineral substrates, leading up to the GOE.