51 巻 (2017) 1 号 p. 29-44
The core and mantle are the main constituents of the Earth, which constrain the physical properties, geochemical and isotopic compositions of the bulk Earth. However, the geochemical composition of the core has not been well constrained, regardless of its importance for better understanding of the geochemical evolution of the Earth. Here we review the current hypotheses of interaction between the mantle and core, and the evolution of the early Earth, and discuss the unsolved problems.
Several radiogenic isotopes such as 186Os–187Os, 182W and 142Nd have been used to elucidate the early evolution of the Earth. In particular, excess of 182W found in the Archean mantle-derived rocks has been ascribed to the core formation and the subsequent “late veneer.”
Heavy element stable isotopes such as cupper and platinum and abundances of highly siderophile elements such as platinum group elements could provide critical information on core segregation and the core-mantle interaction. These chemical data are recently linked closely with the high-pressure and high-temperature experiments, numerical calculations and present seismic observations. However, interpretation of the data is still on debate, which will be also discussed in this review.