11:55 AM - 12:10 PM
[MIS06-10] Oxidizing magma ocean due to redox disproportionation of Fe2+ at high pressures and implications for the atmosphere
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.
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.