Iridium anomaly

The iridium anomaly is an unusually high concentration of iridium in sediment deposited at the Cretaceous–Paleogene boundary, evidence associated with the impact that contributed to the mass extinction.

Cretaceous–Paleogene boundary: The geological boundary marking the end of the Cretaceous Period and the beginning of the Paleogene Period, about 66 million years ago. The anomaly occurs in sediment layers marking this boundary.
Walter Alvarez: An American geologist who helped develop the impact explanation for the end-Cretaceous extinction. He connected the boundary iridium layer to a brief catastrophic event.
Chondritic meteorite: A primitive stony meteorite containing chondrules and preserving material from the early Solar System. Its typical iridium abundance provided a reference for estimating extraterrestrial material in boundary clay.
Bottaccione Gorge: A gorge near Gubbio, Italy, exposing sedimentary rocks that record the Cretaceous–Paleogene boundary. Its boundary clay was the site of the first reported iridium anomaly.
Deccan Traps: A vast volcanic province in India formed by repeated eruptions around the Cretaceous–Paleogene transition. Its volcanism is the leading alternative or contributing cause considered alongside the impact.
Chicxulub impactor: The asteroid whose impact at Chicxulub is linked to the end-Cretaceous mass extinction. An impactor rich in iridium can account for the boundary layer's unusual concentration.
Luis Alvarez: An American physicist who coauthored the 1980 proposal that an asteroid impact caused the end-Cretaceous extinction. His expertise helped interpret the iridium concentration as evidence of an extraterrestrial source.
Siderophile element: An element that preferentially dissolves in metallic iron rather than silicate material during planetary differentiation. Iridium's siderophile behavior helps explain its scarcity in Earth's crust.
Stevns Klint: A coastal cliff in Denmark exposing a fossil-rich record of the Cretaceous–Paleogene boundary. Its boundary layer offers a well-studied European comparison to the Italian discovery site.
Mantle plume: A rising column of anomalously hot mantle that can produce extensive volcanism at Earth's surface. A plume is one proposed driver of Deccan Traps volcanism near the boundary.

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