The origin of Cretaceous-Palaeogene impactor revealed by nickel isotopes

Sixty-six million years ago, non-avian dinosaurs and other taxa went extinct during one of the largest mass extinctions in the history of life on Earth. The extinction was likely caused by an asteroid of unknown origin, responsible for the Chicxulub impact structure. Existing evidence identifies the impactor as an asteroid, similar to carbonaceous chondrites. However, carbonaceous chondrites are a diverse class of meteorites, leaving the exact nature of the impactor unclear. By measuring Ni isotopes in marine clays containing the impact ejecta, we constrain the impactor to one group of carbonaceous chondrites—CO chondrites—and some ungrouped chondrites. This study highlights the use of Ni isotopes in fingerprinting extraterrestrial materials on Earth. Given that CO chondrites are “dry” compared to the other carbonaceous chondrites and would have delivered much less volatiles, which are thought to be essential in causing the extinction, this work allows further studies of the mechanism behind the extinction.