Forming planetary cores without magma oceans: an alternative view from in-situ tomographic imaging at extreme conditions

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• Dr Geoff Bromiley - University of Edinburgh
• Monday 15 October 2018, 17:30-18:30
• Harker 1, Department of Earth Sciences, Downing Street.

If you have a question about this talk, please contact Ben Johnson.

Magma oceans are used to explain many processes in the early solar system, from efficient silicate- metal differentiation in terrestrial planets to formation of the Moon’s flotation crust, and from development of deep compositional heterogeneities in the Earth to efficient mantle degassing and formation of a hydrosphere and atmosphere. It is commonly assumed that a substantial portion of the Earth was melted multiple times during accretion: at least one deep, early magma ocean which kick-started efficient core formation, and a later stage of melting during the Moon-forming event. Chemical exchange between metal and silicate during these magma ocean episodes may have controlled the composition of the silicate portion of Earth. However, recent work casts doubt on the idea that mantle chemistry can be modelled based on silicate-metal equilibration in a deep magma ocean. There is also growing evidence that core segregation began very early in the inner solar system, and in smaller bodies for which magma oceans are harder to invoke.

In this talk, I will summarise evidence for an alternative mechanism for core formation: lower temperature percolation of core-forming liquids through solid silicate. Recent advances in in-situ microtomographic imagining allow us to study complex processes such as core formation directly under deep planetary conditions. By studying textural development in complex systems in real time, we can constrain, for the first time, rates of melt segregation. This allows us to test the efficiency of percolation as a mechanism for core formation, and to consider the influence that this process might have had on the composition of the Earth. As well as introducing current and future developments within the exciting field of ‘extreme conditions microtomography’ I will also discuss the wider implications that this work has on our understanding of planetary geochemistry, and the mechanisms of core formation and segregation in rocky planets.

This talk is part of the Sedgwick Club talks series.

This talk is included in these lists:

• Harker 1, Department of Earth Sciences, Downing Street
• Department of Earth Sciences seminars
• Sedgwick Club talks

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