Behaviors of light elements during early Earth's formation from high-pressure and high-temperature experiments

2021 Fiscal Year Final Research Report

• Project/Area Number: 18K13630
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: The University of Tokyo
• Principal Investigator: Iizuka Riko 東京大学, 大学院理学系研究科(理学部), 客員共同研究員 (80632413)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: 軽元素 / 水素 / 中性子回折 / その場観察 / 地球進化 / 硫黄 / 地球核

Outline of Final Research Achievements

The Earth’s core mainly consists of iron (Fe) and is considered to contain light elements (H, C, O, Si, S) to explain the density deficit compared to pure iron. Hydrogen (H) is one of the promising candidates. However, its amount dissolved in the core and the process are still unknown due to the difficulty in detecting the lightest element via X-ray and obtaining the unquenchable hydrides.
In this study, we investigated the effect of sulfur (S) on the hydrogenation of iron using in-situ neutron diffraction observations at high pressure and high temperature. The obtained H solubility of Fe and FeS in the sample simulating the primitive Earth indicated that iron hydride was formed by the reaction of Fe and water, while FeS is hardly hydrogenated. Both H and S can be incorporated into solid iron, whereas the other light elements could have dissolved into molten iron hydrides and FeS during the later process of the Earth’s evolution.

Free Research Field

高圧地球科学、地球深部物質学

Academic Significance and Societal Importance of the Research Achievements

高温高圧実験とパルス中性子という先端量子ビームの利用を組み合わせ、地球深部に存在する鉄や含水鉱物の結晶構造や物性、反応や化学形態について調べることで、これまでは実験的に難しいとされてきた高温高圧下での鉄中の水素の挙動を解明した。汎用的な高圧セルや放射光X線用の高解像度イメージングカメラを構築したという点で高温高圧実験の技術開発・改良に貢献しただけでなく、実験によって得られた物質科学的な知見から地球の成り立ちについて新たなシナリオを提唱したことに、学術的な意義が見出される。