| Project/Area Number |
18540470
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | The University of Tokyo |
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Principal Investigator |
MURAKAMI Takashi The University of Tokyo, Graduate School of Science, Professor (00253295)
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| Co-Investigator(Kenkyū-buntansha) |
KOGURE Toshihiro The University of Tokyo, Graduate School of Science, Associate Professor (50282728)
TSUKIMURA Katsuhiro Advanced Industrial Science and Technology, 産業技術総合研究所, Senior Scientist (20357510)
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| Project Period (FY) |
2006 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥3,820,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥420,000)
Fiscal Year 2007: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
Fiscal Year 2006: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Keywords | Atmospheric evolution / oxidation rate / weathering / modelling |
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| Research Abstract |
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 PO 2 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.
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