Raton Iridium Layer

Atop Goat Hill in Raton, New Mexico lies a layer of rock that tells a story that is guaranteed to intrigue more than just ardent geologists. A thin layer of iridium-rich rock is found here - a layer that is found in several places all over the world. Radiometric dating of these layers found that they actually mark the boundary between the Cretaceous and Paleogene periods.

An anomalous iridium layer was first discovered in the 1980s in Gubbio, Italy. The concentration of iridium was notable because iridium, while uncommon on the Earth’s surface, is very common in asteroids. Two American scientists, Luis Alvarez and his son Walter proposed that the iridium concentration was caused by an enormous meteor impact, which coated the world in asteroid dust and also ended the Cretaceous period. 

However, since every K-Pg site had been found in marine sedimentary rock, it was also possible that the iridium could have come from the ocean, where iridium concentrations are higher. This led Charles Orth, Chuck Pillmore, and scientists from Los Alamos National Laboratory to search for boundaries relating to this event in non-marine rock.

Pillmore’s familiarity with the Raton Basin led the team to find other iridium anomalies throughout the local area, verifying the extraterrestrial origin of the iridium anomaly. The discovery of the Mexican Chicxulub Crater corroborated the Alvarez hypothesis and further bolstered the belief that a meteor impact killed the dinosaurs.