The Origin of the Asteroid That Killed the Dinosaurs

T he end of the story is written, literally, in stone. Before a rock from space smashed into Earth and wiped out much of life some 66 million years ago, the rock had a long story of its own—one scientists have known surprisingly little about. Where exactly did it come from, and what does it mean for future impacts that might pose a threat to humanity? 

For decades, the prevailing idea has been that the impactor was an asteroid rather than a comet or something else—although a few scientists in the past argued for alternate interpretations for the non-avian dinosaurs’ demise related to widespread volcanism or sea-level regression. A newly published analysis supports the theory that the doom-bringing rock was indeed an asteroid. It also clarifies its origin story: It was likely born far out in the early solar system, beyond Jupiter’s orbit, before it plunged closer to the sun, eventually crashing down and ruining the dinosaurs’ party. The researchers, led by cosmochemist Mario Fischer-Gödde, at the University of Cologne, published their measurements recently in Science.

The evidence for the impact, of course, is spread across the globe, in thin layers below our feet. Decades of geological measurements have found that this geologic boundary, the Cretaceous-Paleogene (K-Pg), is more enriched in rare elements, such as iridium, compared with neighboring layers of rock. Guess what else contains a lot of iridium? Meteorites, the fragments of asteroids that have fallen to Earth. 

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