Nanoparticles of iridium and other platinum group elements identified in Chicxulub asteroid impact spherules – Implications for impact winter and profound climate change

Abstract

The Chicxulub asteroid that ended the Cretaceous Era ∼66.05 million years ago caused a prolonged time of global darkness – the impact winter – leading to mass extinctions. Elements from the asteroid, including the platinum group elements (PGEs) osmium, iridium and platinum are known from the globally distributed boundary clay but their carrier elements have so far been unknown. We identify, for the first time in detail, the presence of these PGEs within Chicxulub impact spherules and importantly, we identify their carrier elements. We show through synchrotron Nano-XRF how these PGEs occur in nanostructures as un-ordered cube- and/or needle-like crystals co-localizing with both siderophile and chalcophile elements including Co, Ni, Cu, Zn, and Pb, derived from the asteroid. These crystals are set within a matrix of iron-rich calcium and silica glass revealing the mix of vaporized target rock and the asteroid. The results provide insights into the combination of elements present in the spherules, indicating formation of new minerals. We argue that the nano-shards of unreactive elements such as platinum, iridium and copper acted as nuclei for aerosol formation and potentially contributed to a prolonged impact winter with darkness and cooling leading to a profound and long-term climate change.This work was supported by Swedish Research Council, Sweden, grants VR 2019-4061 (V·V.); and Knut and Alice Wallenberg Foundation, Sweden, grant KAW 2020.0145  (V·V.), and Wenner-Gren Foundation SSh2023-0016, Sweden (V·V.). We thank beamline scientists and staff at MAX IV synchrotron facility. We acknowledge MAX IV Laboratory for time on Beamline NanoMAX under Proposal 20190340 and Beamline Balder, Sweden, under Proposal 20210384. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council, Sweden under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas, Sweden, under contract 2019-02496. XRM data acquisition was supported by a grant to the Stockholm University Brain Imaging Centre, Sweden (SU FV-5.1.2-1035-15).</p