Wikipedia Iridium
Iridium is a chemical element in the periodic table that has the symbol Ir and atomic number 77. A heavy, very hard, brittle, silvery-white transition metal of the platinum family, iridium is used in high strength alloys that can withstand high temperatures and occurs in natural alloys with platinum or osmium. Iridium is notable for being the most corrosion resistant element known and for its association with the demise of the dinosaurs. It is used in high temperature apparatus, electrical contacts, and as a hardening agent for platinum.
The KT event of 65 million years ago, marking the temporal border between the Cretaceous and Tertiary eras of geological time, was identified by a thin stratum of iridium-rich clay. A team led by Luis Alvarez (1980) proposed an extraterrestrial origin for this iridium, attributing it to an asteroid or comet impact near what is now Yucatan Peninsula. Their theory is widely accepted to explain the demise of the dinosaurs. Dewey M. McLean and others argue that the iridium may have been of volcanic origin instead. The Earth's core is rich in iridium, and Piton de la Fournaise on Réunion, for example, is still releasing iridium today.