Evolution of the Atmosphere, Ocean, Crust, and Biosphere

本项目的主要目标是通过对该时期形成的各种岩石的详细地球化学调查，包括带状铁地层、古土壤、含铀石英卵石砾岩、页岩、碳酸盐岩和火山岩，建立3.5 - 0.5 Ga期间大气氧演化及其与生物演化的联系的定量模型。1998年和1999年的夏天，在南非、纳米比亚和澳大利亚对这类岩石进行了实地调查。本项目获得的各类地球化学数据均与我们的含氧大气和多样化生物圈早期发展模式相一致。以下是对新发现的简要总结。最古老的古土壤部分显示出显著的铁损失是在澳大利亚西部2.8 Ga的Mt. Roe玄武岩上发育的。然而，Nedachi等人强烈认为，Roe山古土壤中铁的损失更多是由温度为~ 200 ~ ~ 100℃的含ch4的热液引起的，而不是由土壤形成过程中的地表水引起的。CWKH模式的提倡者采用了2.2 Ga前石英-卵石砾岩中铀矿和黄铁矿颗粒为碎屑成因的解释。Ono等人（论文#4）报告了对加拿大埃利奥特湖区~ 2.4 Ga石英卵石砾岩中各种矿物的纹理、化学成分和同位素组成进行小规模详细分析的结果。根据新的铀矿溶解动力学实验数据，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多年。因此，存在或不存在的铀质碎屑颗粒可能不能用来限制大气pO2水平。太古宙页岩的地球化学特征、枕状熔岩边缘Fe3+/Fe2+比值的增加、BIF的起源以及BIF中早期氧化大气发育的证据均得到了相同的结论

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