Evolution of the Atmosphere, Ocean, Crust, and Biosphere

该项目的主要目标是通过对3.5 Ga至0.5 Ga期间形成的各种岩石进行详细的地球化学调查，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，建立大气氧演化及其与生物演化关系的定量模型。1998年和1999年夏季在南非、纳米比亚和澳大利亚进行了这类岩石的野外调查。最古老的古土壤剖面显示出铁的显著损失，这些剖面是在2.8 Ga Mt.澳大利亚西部的鱼卵玄武岩。Nedachi等人，然而，强烈表明，铁的损失从山。Roe ...更多信息 CWKH模型的支持者认为2.2Ga前石英砾砾岩中的晶质铀矿和黄铁矿颗粒是碎屑成因的，但在2.2Ga前石英砾砾岩中的晶质铀矿和黄铁矿颗粒是碎屑成因的，而在2.2Ga前石英砾砾岩中的晶质铀矿和黄铁矿颗粒是碎屑成因的。Ono等人（论文4）报道了对加拿大Elliot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尺度详细分析结果，根据晶质铀矿溶解动力学的新实验数据，Ono和Ohmoto得出结论，典型的晶质铀矿颗粒在目前的大气条件下可以存活超过1000年。因此，晶质铀矿碎屑颗粒的存在与否可能不能用来限制大气pO 2水平。从太古代页岩的地球化学、枕状熔岩边缘增加的Fe 3 +/Fe 2+比值、BIF的起源以及BIFs中含氧大气早期发展的证据中得出了相同的结论。

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