The term iridium anomaly refers to a much higher amount of the element iridium found in a rock layer at the Cretaceous–Paleogene (K–Pg) boundary. This unusually large amount of a rare metal, such as iridium, is often used as evidence for an event caused by something from space.

Anomaly characteristics

The location where this iridium anomaly was first discovered is near Raton, New Mexico. Iridium is a very rare element in Earth's crust, but it is found in much higher than usual amounts (about 100 times more than normal) in a thin layer of clay found worldwide. This clay layer marks the boundary between the Cretaceous and Paleogene periods, which occurred 66 million years ago. This boundary is linked to a major extinction event, including the extinction of the dinosaurs and about 70% of all other species. The clay layer also contains tiny grains of shocked quartz and, in some areas, small weathered glass beads that may be tektites.

Meteorite impact theory

A group of scientists, including physicist Luis Alvarez, his son geologist Walter Alvarez, and chemists Frank Asaro and Helen Vaughn Michel, were the first to connect the extinction event to an impact caused by something from space. They made this discovery because they noticed that iridium is found in much higher amounts in meteorites than it is on Earth. Later, this theory was confirmed by additional evidence, such as the discovery of the impact crater called Chicxulub on the Yucatán Peninsula in Mexico.