Light from tungsten on core construction

Abstract

The Earth's iron core is thought to be almost as old as the Earth itself (approaching 4.6 billion years) but there are different opinions as to how quickly and in what manner it formed. Core formation times as short as 10 million years or longer than the time to accrete the Earth (around 100 Myr) have been suggested. This question is very relevant to how planets are assembled and how all the terrestrial reservoirs (ocean, atmosphere and mantle as well as core) are established, and it can only be addressed by radioisotopic dating methods. In this regard, a promising development is hafnium- tungsten chronometry, and on page 771 of this issue, Lee and Hallidai use this approach to infer that the core formation took longer than about 60 million years. Moreover, their interpretation of new meteoritic data implies that there must have been an unexpectedly high level of ^(182)Hf in the early Solar System.