Ir和其他地壳中亏损的亲铁元素,当海相微体古生物灭绝时,在同一地层层位上形成了异常高的富集,据古生物灭绝所确定的白垩系与第三系的界限大约为距今65到67百万年。这种地球化学异常在世界范围内的海相和陆相沉积物中均已发现。详细的地球化学研究表明,这种异常是由于一个成份可能相当于碳质球粒陨石、直径为10公里的球外物体冲击地球而引起的。白垩纪末期灭绝事件的冲击假说指出:在其他发生大量灭绝事件的地层中也可发现球外物体冲击 Ir and other crustal iron loss elements, when the marine microfacies paleozoan extinction, the formation of the same stratigraphic level abnormally high enrichment, according to paleontological extinction identified Cretaceous and Tertiary boundaries of about 65 to 67 million years ago. This geochemical anomaly has been found in marine and continental sediments worldwide. Detailed geochemical studies have shown that this anomaly is due to a component may be equivalent to the carbonaceous chondrites, the diameter of 10 kilometers of extra-corpuscles caused by the impact of the Earth. The impact hypothesis of the extinction event at the end of the Cretaceous indicates that the impact of extra-granular objects can also be found in other formations where a large number of extinction events occur