Evolution of the Atmosphere, Ocean, Crust, and Biosphere

该项目的主要目标是通过对3.5Ga至0.5Ga期间形成的各种岩石的详细地球化学调查，建立大气氧的演化及其与生物演化的联系的定量模型，这些岩石包括条状铁建造、古土壤、含铀石英卵石砾岩、页岩、碳酸盐和火山岩。1998年和1999年夏季在南非、纳米比亚和澳大利亚对这类岩石进行了野外调查。在这个项目中获得的各种类型的地球化学数据都与我们关于早期含氧大气和多样化生物圈发育的模型一致。以下是新发现的简要总结。显示铁显著丧失的最古老的古土壤剖面是在2.8GaMt形成的剖面。澳大利亚西部的罗伊玄武岩。然而，Nedachi等人强烈建议，从山上流失的铁。Roe…更多的古土壤是由~2 0 0~~10 0℃的含甲烷热液造成的，而不是由土壤形成过程中的地表水造成的。Ono et al.(论文#4)报道了对加拿大埃利奥特湖地区~2.4Ga石英-卵石砾岩中各种矿物的结构、化学成分和同位素组成的小规模、详细的分析结果。根据关于铀矿溶解动力学的最新实验数据，Ono和Ohmoto得出结论：在目前的大气条件下，典型的铀矿颗粒可以存活1000年以上。从太古宙页岩的地球化学、枕状熔岩边缘Fe3+/Fe2+比值的增加、BIF的起源以及BIF中早期含氧大气发育的证据中，都得到了同样的结论

The primary objective of this project is to develop a quantitative model for the evolution of atmospheric oxygen and its connection to the evolution of organisms during the period between 3.5 Ga and 0.5 Ga, from detailed geochemical investigations of a variety of rocks formed during this period, including banded iron formations, paleosols, uraniferous quartz pebble conglomerates, shales, carbonates, and volcanic rocks. Field investigations of these types of rocks were carried out in South Africa, Namibia, and Australia in the summers of 1998 and 1999.Various types of geochemical data obtained in this project are all consistent with the our model for the early development of an oxygenated atmosphere and of a diverse biosphere. The following are brief summaries of new findings.The oldest paleosol sections that show a significant loss of Fe are those developed on the 2.8 Ga Mt. Roe basalt in western Australia. Nedachi et al., however, strongly suggest that the loss of Fe from the Mt. Roe … More paleosols was caused by CH4-bearing hydrothermal solutions with temperatures of 〜200 - 〜100℃, rather than by the surface water during soil formation.The advocates of the CWKH model have adapted the interpretation that the grains of uraninite and pyrite in pre-2.2 Ga quartz-pebble conglomerates are of detrital origin. Ono et al. (Paper #4) report the results of a small-scale, detailed analyses of textures, chemical composition, and isotopic composition of a variety of minerals in 〜2.4 Ga quartz-pebble conglomerates from the Elliot Lake district, Canada.Based on new experimental data on the dissolution kinetics of uraninite, Ono and Ohmoto conclude that typical grains of uraninite can survive for more than 1000 years under the present atmospheric condition. Therefore, the presence or absence of detrital grains of uraninite may not be used to constrain the atmospheric pO2 level.The same conclusions were obtained from the geochemistry of the Archean shale, increased Fe3+/Fe2+ ratios in the rims of pillow lava, origins of BIF, and evidence in BIFs for the early development of an oxygenated atmosphere Less