Siderophilic element concentrations are high in sediments from the Cretaceous-Tertiary boundary. An extraterrestrial source is indicated. Concentrations are too high to be understood in terms of the impact of a chondritic asteroid. Either the projectile was a metal-sulphide core or the infalling material (probably weak cometary matter) was slowed down during atmospheric passage.
Supplement to: Kyte, Frank T; Zhou, Zhiming; Wasson, John T (1980): Siderophile-enriched sediments from the Cretaceous-Tertiary boundary. Nature, 288(5792), 651-656