This article included a query about the prevalence of iridium at the K-T boundary. The global average of iridium levels in the boundary layer is 15 times the background level, peaking at 160 times background near the crater (Alvarez et al, 1980.) | This article included a query about the prevalence of iridium at the K-T boundary. The global average of iridium levels in the boundary layer is 15 times the background level, peaking at 160 times background near the crater (Alvarez et al, 1980.) |