An impact at Chicxulub, Mexico, occurred 66 million years ago, producing a global stratigraphic layer that marks the boundary between the Cretaceous and Paleogene eras. That layer contains elevated concentrations of platinum-group elements, including ruthenium. We measured ruthenium isotopes in samples taken from three Cretaceous-Paleogene boundary sites, five other impacts that occurred between 36 million to 470 million years ago, and ancient 3.5-billion- to 3.2-billion-year-old impact spherule layers. Our data indicate that the Chicxulub impactor was a carbonaceous-type asteroid, which had formed beyond the orbit of Jupiter. The five other impact structures have isotopic signatures that are more consistent with siliceous-type asteroids, which formed closer to the Sun. The ancient spherule layer samples are consistent with impacts of carbonaceous-type asteroids during Earth’s final stages of accretion.

中文翻译：

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钌同位素显示希克苏鲁伯撞击器是一颗碳质型小行星


6600 万年前发生在墨西哥希克苏鲁伯的一次撞击，产生了一个全球地层，标志着白垩纪和古近纪之间的边界。该层含有高浓度的铂族元素，包括钌。我们测量了取自三个白垩纪-古近纪边界地点、发生在 3600 万至 4.7 亿年前的其他五次撞击以及 35 亿至 32 亿年前撞击球层的样本中的钌同位素。我们的数据表明希克苏鲁伯撞击器是一颗碳质型小行星，形成于木星轨道之外。其他五个撞击结构的同位素特征与硅质型小行星更加一致，硅质型小行星形成的距离太阳更近。古老的球体层样本与地球吸积最后阶段碳质型小行星的撞击一致。