iridium anomaly
英[ɪˈrɪdi:əm əˈnɔməli:]美[ɪˈrɪdiəm əˈnɑməli]
The term iridium anomaly commonly refers to an unusual abundance of the chemical element iridium in a layer of rock strata, often taken as evidence of an extraterrestrial impact event because of the case of such an anomaly at the Cretaceous–Paleogene boundary (often abbreviated either K-Pg boundary or K–T boundary).