Evolution and spread of the microbe accompanied paleoenvironmental fluctuation

前寒武纪大气中的氧浓度在过去的十年里得到了广泛的研究，主要是因为它与地球表面的环境，特别是与生命的演化密切相关。在对古土壤、古风化土壤、硫同位素等物理化学分析的基础上，提出了大气氧的演化模式。然而，在28亿到18亿年前，当大气氧被认为是地球历史上第一次上升时，还没有对大气氧水平进行定量估计。我们开发了一种可以控制氧浓度的手套箱，可以进行矿物溶解实验。通过橄榄石与水的反应来模拟手套箱中的风化作用，并考察了铁的再分配。在氧分压(PO2)为0.2atm和10(-4)atm时，体系中铁的氧化残留率分别为0.92和0.15。这一结果与在古土壤中观察到的结果是一致的。在此基础上，综合考虑矿物溶解速率、铁氧化速率和地下水流量等因素，建立了铁在风化过程中的行为模型。建立了风化剖面中Fe(III)/Fe(II)浓度比与PO2之间的定量关系。估算表明，pH和地下水流量影响这些关系，但矿物溶解速率或风化剖面的形成时间不影响这些关系。模型在古土壤中的应用表明，大气氧在25亿至120亿年前逐渐上升。

Atmospheric oxygen concentration in the Precambrian has been intensively studied for the past decade mainly because it is closely related to the environment of the Earth's surface, especially life evolution. Evolution models of atmospheric oxygen have been proposed based on physical and chemical analysis of paleosols, soils formed by ancient weathering, sulfur isotopes and so on. However, quantitative estimation of atmospheric oxygen levels have not been made between 2.8 and 1.8 billion years ago when atmospheric oxygen is considered to rise for the first time in the Earth's history. We developed a glove box which can control oxygen concentration and make us carry out mineral dissolution experiment We mimicked weathering in the glove box by reacting olivine with water, and examined Fe redistribution. The ratio of Fe oxidized and remaining in the system was 0.92 at 0.2 atm of partial pressure of oxygen (PO2) and 0.15 at 10(-4) atm. The results were well agreed with those observed in the paleosols. We, then made a model of Fe behavior during weathering considering the factors, dissolution rate of a mineral, Fe oxidation rate and groundwater flow rate. We derived a differential equation from the model and estimated the relationships between the concentration ratio of Fe(III) to Fe(II) in a weathering profile and PO2 quantitatively. The estimation has indicated that pH and groundwater flow rate affect the relationships but mineral dissolution rate or formation time of a weathering profile do not. The application of the model to paleosols has revealed that atmospheric oxygen rose gradually between 2.5 and 12.0 billion years ago.