2017 年 27 巻 4 号 p. 246-255
Geochemical tools such as the chemical and isotopic compositions of the samples with a wide range of ages have revealed the chemical evolution of the Earth. A model of the very early history of the earth with accumulation of the planetesimal, the giant impact, core segregation and late veneer has been proposed based on siderophile element abundance and isotopic composition of the old mantle-derived rocks. Especially, late veneer following core segregation hypothesis is supported by evidence that gradual increase with time in platinum group elements abundance of komatiite originated from deep mantle and the chondritic Os isotopic evolution of the earth's mantle. 182W (decay product of extinct 182Hf) anomaly relative to present-day mantle value of komatiite and modern ocean island basalt has indicated core-mantle interaction. These models have been proposed based on geochemical studies, but they still have many unclear problems. In line of this, it is very important to precisely constrain the behaviors and partition coefficients of the elements under deep-earth conditions. Here we mention these problems and propose importance of constraints by high-pressure and high-temperature experiments to provide data on behavior of elements, especially siderophile elements.