2022 Fiscal Year Final Research Report
Construction of Earth formation model by isotopic analysis of siderophile elements in meteorites and Archean igneous rocks
| Project/Area Number |
19H00715
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Review Section |
Medium-sized Section 17:Earth and planetary science and related fields
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
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| Co-Investigator(Kenkyū-buntansha) |
石川 晃 東京工業大学, 理学院, 准教授 (20524507)
玄田 英典 東京工業大学, 地球生命研究所, 教授 (90456260)
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| Project Period (FY) |
2019-04-01 – 2023-03-31
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| Keywords | 親鉄元素 / 同位体異常 / 地球形成モデル / 太古代火成岩 / 隕石 |
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| Outline of Final Research Achievements |
This study focuses on the "HSE isotope paradox of the terrestrial mantle", in which the Mo isotopic composition of the Earth's mantle cannot be explained by those of currently accessible meteorites. In this study, we measured the Mo isotopic compositions of Archean rock samples and found no nucleosynthetic Mo isotopic anomalies exceeding the analytical uncertainties. Numerical simulations of the Earth accumulation model developed in this study show that 90% of the Earth's building blocks are NC-like and 10% are CC-like materials, and that the materials added during late accretion are composed in the same proportions as the Earth's building blocks. Although this result contradicts the conventional hypothesis that CC-like materials were added during late accretion, it is consistent with our analysis that there is no significant difference in the Mo isotopic composition of the Archean and modern mantle samples.
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| Free Research Field |
宇宙地球化学
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| Academic Significance and Societal Importance of the Research Achievements |
地球の原材料や形成過程を解明することは、地球惑星科学分野の根幹をなす重要課題である。従来、原始地球は太陽系内側領域に存在したNC的物質を材料に作られ、最後に太陽系の遠方に由来するCC的物質が降り注いだことにより地球が完成したと考えられてきた。しかし、本研究により、地球原材料の90%はNC的、10%はCC的物質であり、後期集積で加わった物質も地球原材料と同じ比率で構成されることが判明した。このことが、太古代試料にMo同位体異常が見られないことの本質的原因であると結論付けられる。このように、本研究は地球形成に関する従来の描像を刷新したといえる。
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