地球地壳的铱Ir含量很低(0.001μg/g)(陨石可达0.65μg/g)，在全球上百处的KTB（白垩纪末-新生纪初的界面）黏土层中发现有Ir富集，即Ir含量比该黏土层上部和下部的Ir平均含量高数倍到数十倍。
这一铱异常为阿尔瓦雷斯假说提供了强有力的支持，尽管小行星本身从未被发现。
This iridium anomaly offers strong support for the Alvarez hypothesis even though no asteroid itself has ever been discovered.
用地壳元素钪进行标准化之后，铱异常十分明显，而其它元素在界线附近则没有变化。
After normalized with the typical terrestrial element Sc, iridium shows marked enrichment at the B/M boundary;
前人在该套地层底部发现了铱等元素异常，认为可作为划分其地质时代的依据。
Some elementary anomalies of indium and other elements have been found at the bottom of the stratum, it can be used as the evidence to separate geological era.
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