水の行方 –地球初期進化への新たな問題提起–

抄録

The fate of H₂O accreted to the primordial Earth is discussed using the results of the hydrogen partitioning experiments between molten iron and silicate melt at high pressure. Previous works related to this problem give no weight to the partitioning of hydrogen into the core, so that the origin and abundance of H₂O in the hydrosphere, crust and mantle of the present Earth should be reconsidered from the viewpoint of the evolution of the primordial Earth including core formation processes. The results indicate that there is large possibility for most of H₂O accreted to the Earth to be transported into the core as molten iron hydride (FeHx), rather than to be left into the hydrosphere and mantle in every case of H₂O concentration in the accreting planetesimals. In other words, the mantle must have been dried up after the core formation. These results are consistent with the observed H₂O concentration in the hydrosphere, crust and upper mantle of the present Earth. The presence of hydrogen in the core may quantitatively settle the problem of density deficit of the present Earth's core.