What I've been reading, featuring the Cretaceous-Paleogene extinction event and the infuriating etymology of narwhals

  • Was intrigued by this excerpt on the basis for the asteroid theory of dinosaur extinction. I was interested since like everyone, I was aware it was the prevailing explanation but had always been taught to beware it was unsettled science and never learned the basis for its favored status. Too interesting that the theory’s originator also contributed to the Manhattan Project and the design of the nuclear bomb dropped on Nagasaki.

With the help of his father, Alvarez had samples of the clay analysed for iridium, a heavy metal that is rarely found on Earth’s surface, but which is common in space, and which falls from the heavens as cosmic dust at a fairly constant rate. The Alvarezes were trying to ascertain how quickly or slowly the band had been deposited. If one assumes the typical pace of accumulation, a large amount of iridium would suggest it had taken a long time, indicating that the extinction process may also have been lengthy; a small amount would suggest that a quick event had overtaken the Earth. But the samples contained a surprise: huge amounts of iridium, so much that it would have taken tens or hundreds of millions of years to deposit at background rates. What could explain it? The Alvarezes came to a radical conclusion: the high concentration of iridium in the band must have come from outer space, and it must have been delivered in bulk by a colossal asteroid strike – an event destructive enough to have triggered the end-Cretaceous extinction. The iridium-rich clay band at Gubbio was the shroud of dust and debris that had eventually settled on a devastated world.

As the same iridium anomaly began to be detected at sites around the world, the Alvarezes’ notion of an asteroid strike followed by the blotting out of the sun was substantiated. It also had an influence beyond palaeontology; when Brusatte describes the aftermath of the impact as being like a nuclear winter, he is gently reverse-engineering the concept, for the idea of a nuclear winter – the darkening and cooling of the world by the dust thrown into the atmosphere after a nuclear exchange – was explored and popularised in the 1980s partly with reference to the Alvarez hypothesis. Meanwhile, the iridium testing and the hypothesis itself came of the Alvarezes’ connections to nuclear science. Luis Alvarez had been a key player in the Manhattan Project, and had helped design ‘Fat Man’, the bomb that was dropped on Nagasaki.

The title of the article derives from the author contemplating the modern-day relevance of the end-Cretaceous event eliminating all dinosaurs but not other animals: “When there is sudden global environmental and climate change, what lives and what dies?” And before you reject the assumption there, it acknowledges "the realisation that birds are dinosaurs is probably the single most important fact ever discovered by dinosaur palaeontologists.”

Also, the article begins with a graphic description of the extinction event, but I find it pales in comparison to this one from a different book:


Still, there are a small minority of holdouts in the debate, such as Prof. Gerta Keller of Princeton, who is a proponent of the Deccan Traps explanation, which attributes dinosaur extinction mostly to a series of volcanic eruptions in West India. The Atlantic had a lengthy article last year on the academic debate surrounding the end-Cretaceous event titled “The Nastiest Feud in Science” featuring some ad hominem attacks and cross-disciplinary antagonism with dissenters fearing for their careers, which makes the natural and social sciences seem not so different after all. It’s more a fascinating portrait of academic hostility on an apolitical topic than an educational one that reliably weighs the balance of evidence, I think. I myself am partial to this theory: