日本地球惑星科学連合2022年大会

講演情報

[E] 口頭発表

セッション記号 M (領域外・複数領域) » M-IS ジョイント

[M-IS06] アストロバイオロジー

2022年5月25日(水) 10:45 〜 12:15 304 (幕張メッセ国際会議場)

コンビーナ:藤島 皓介(東京工業大学地球生命研究所)、コンビーナ:薮田 ひかる(広島大学大学院理学研究科地球惑星システム学専攻)、杉田 精司(東京大学大学院理学系研究科地球惑星科学専攻)、コンビーナ:深川 美里(国立天文台)、座長:深川 美里(国立天文台)、薮田 ひかる(広島大学大学院理学研究科地球惑星システム学専攻)

11:55 〜 12:10

[MIS06-10] Oxidizing magma ocean due to redox disproportionation of Fe2+ at high pressures and implications for the atmosphere

*Hideharu Kuwahara1、Ryoichi Nakada2Shintaro Kadoya3Takashi Yoshino4Tetsuo Irifune1 (1.Geodynamics Research Center, Ehime University、2.Kochi Institute for Core Sample Research, JAMSTEC、3.Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), JAMSTEC、4.Institute for Planetary Materials, Okayama University)

Degassing of volatiles from the mantle of terrestrial planets would have played a key role in the formation of the earliest atmosphere. Because the molecular composition of degassed volatiles from the planetary interior is mainly controlled by the redox state of the mantle [e.g., 1, 2], elucidating the redox state and its history of the earliest Earth’s mantle provides key insights into the formation of the habitable environment of the planet.
Despite the reducing nature of terrestrial magma ocean during core formation, geological evidence shows that the early Earth’s upper mantle around 4.4 billion years ago (immediately after the formation of the Earth) may have already been oxidized close to today [3]. This indicates that the earliest Earth’s mantle had experienced the great oxidation. To explain the great mantle oxidation after the core formation, The redox disproportionation of ferrous iron (Fe2+) to ferric iron (Fe3+) has been invoked [1, 4]. However, the regulation mechanism of the redox state of terrestrial magma ocean is still poorly understood.
Here we show experimental evidence that one order of magnitude higher amounts of Fe3+ than the present Earth’s upper mantle may have been produced via Fe2+ disproportionation in a deep magma ocean. To explain the redox state of the Earth’s upper mantle around 4.4 billion years ago and afterward, we propose that an oxygen sink, such as nebular-derived hydrogen and/or a crystallizing Fe3+-rich lower mantle during the formation of the Earth, is necessary. In this presentation, we will also talk about implications of our results for planetary atmospheres before and after the origin of life.

References: [1] Hirschmann, 2012, Earth and Planetary Science Letters 341-344, 48-57. [2] Gaillard and Scaillet, 2014, Earth and Planetary Science Letters 403, 307-316. [3] Trail et al., 2011, Nature 480, 79-82. [4] Armstrong et al., 2019, Science 365, 903-906.