August 2025

The ¹⁸⁷Re–¹⁸⁷Os system offers a unique perspective among the isotopic approaches used to understand planetary evolution because of the chalcophile and siderophile affinities of the parent and daughter elements and their contrasting behaviors during partial melting. Considered the geochronometer of choice to study the Earth’s mantle, from the scale of individual minerals to large-scale outcrops, this system has revealed the survival of Archean and Proterozoic mantle in younger tectonic settings, and has demonstrated local to regional coupling, and sometimes decoupling, between the crust and mantle. Osmium isotopes are also key tracers of melt–peridotite and mantle–crust interactions and recycling processes in subduction zones, and have furthered our understanding of the origin of multi-scale geochemical and isotopic heterogeneities.

The siderophile elements, which include Re, Pt, Os, and W, directly constrain the accretionary history of Earth. The largely chondritic ¹⁸⁶,¹⁸⁷Os/¹⁸⁸Os ratios of Earth’s mantle, coupled with excesses in siderophile element abundances, provide nearly incontrovertible evidence that some meteoritic addition continued after core formation was complete. Osmium and W isotope systematics of plume-derived mafic-ultramafic rocks reveal the complex chemical evolution of their deep mantle sources. In the upper mantle, Re-Os dating of whole-rock xenoliths and sulfide inclusions in diamonds hosted by kimberlites indicate both ancient melt depletion and subsequent modification of the mantle lithosphere beneath the earliest continents, with Re-Os ages of eclogitic diamonds possibly recording the transition to a sustained plate tectonic regime on Earth.

The exceptional power and versatility of the Re-Os radioactive decay system for Earth science stems from the distinctive geochemical behavior of its constituent elements. Here, we first explain how the positions of Re and Os in the periodic table are responsible for their highly siderophile, chalcophile, and organophile properties. We then discuss how these properties dictate the distribution of Re and Os within and at the surface of the Earth and other planetary bodies. Lastly, we describe how the analytical challenges posed by the unusual geochemistry of these elements were overcome with major technological advances, leading to a dramatic decrease in the amount of sample material required for Re-Os isotopic analysis, thereby sparking an explosion of new applications.