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  3. Abstract

    Magma oceans were once ubiquitous in the early solar system, setting up the initial conditions for different evolutionary paths of planetary bodies. In particular, the redox conditions of magma oceans may have profound influence on the redox state of subsequently formed mantles and the overlying atmospheres. The relevant redox buffering reactions, however, remain poorly constrained. Using first-principles simulations combined with thermodynamic modeling, we show that magma oceans of Earth, Mars, and the Moon are likely characterized with a vertical gradient in oxygen fugacity with deeper magma oceans invoking more oxidizing surface conditions. This redox zonation may be the major cause for the Earth’s upper mantle being more oxidized than Mars’ and the Moon’s. These contrasting redox profiles also suggest that Earth’s early atmosphere was dominated by CO2and H2O, in contrast to those enriched in H2O and H2for Mars, and H2and CO for the Moon.

     
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  4. Abstract

    MgO exsolution has been proposed to drive an early geodynamo. Experimental studies, however, have drawn different conclusions regarding the applicability of MgO exsolution. While many studies suggest that significant Mg can dissolve into the Earth's core, the amount of MgO exsolved out of the core, which hinges on the temperature dependence of MgO solubility, remains unclear. Here we present new high‐temperature experiments to better constrain the temperature and compositional dependence of Mg partitioning between Fe alloys and silicate liquids. Our experiments show that Mg partitioning is weakly dependent on temperature, while confirming its strong dependence on oxygen content in Fe alloys. This implies that MgO exolution is limited as the core cools but can help drive an early geodyanamo if the core heat loss is slightly subadiabatic. If an exosolution‐driven geodynamo did occur, it was likely over a limited time span that depends on the core thermal history and conductivity.

     
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  5. Abstract

    Density of silicate melt dictates melt migration and establishes the gross structure of Earth's interior. However, due to technical challenges, the melt density of relevant compositions is poorly known at deep mantle conditions. Particularly, water may be dissolved in such melts in large amounts and can potentially affect their density at extreme pressure and temperature conditions. Here we perform first‐principles molecular dynamics simulations to evaluate the density of Fe‐rich, eutectic‐like silicate melt (Emelt) with varying water content up to about 12 wt %. Our results show that water mixes nearly ideally with the nonvolatile component in silicate melt and can decrease the melt density significantly. They also suggest that hydrous melts can be gravitationally stable in the lowermost mantle given its likely high iron content, providing a mechanism to explain seismically slow and dense layers near the core‐mantle boundary.

     
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