PSuddenly, with fire and from above – the impact of a ten to fifteen kilometer wide asteroid 66 million years ago fulfills all popular notions of the end of the world. And indeed, between 57 and 83 percent of all animal species on land and in the sea suddenly disappeared from the scene at that time – including all dinosaur groups except the ancestors of birds. The “KT Event,” which not only separates the Cretaceous (K) from the Tertiary (T), but also ended the Mesozoic and ushered in the Cenozoic, marked the fifth major extinction event since animals first appeared 541 million years ago . And inasmuch as the KT event is an immediate prerequisite for the mammalian ascension, it is also the most important from our human perspective.
Whether the impact and its consequences alone were responsible for this, or whether long-lasting volcanic eruptions in India were also responsible, has long been the subject of a sometimes heated specialist controversy, which is also due to a glaring data problem: sufficient fossil-bearing deposits from the very last section of the Cretaceous period, the Maastrichian, are extremely rare obtain.
Fish kills in glass rain
Now, however, two research groups have even succeeded in making a statement regarding the season at which the disaster struck the biosphere. This was possible thanks to a layer of sediment that the American paleontologist Robert DePalma, a cousin of film director Brian DePalma, who is now researching in Manchester, UK, encountered in 2012 in western North Dakota. He named the site “Tanis” and placed it in one with some prominent experts on the KT event 2019 published publication geological one. Accordingly, the deposit dates precisely from the time of the catastrophe.
The Tanis deposits contain large amounts of fossils of freshwater fish, sturgeons and paddlefish, among others, all of which appear to have been swept together by a violent wave onto what geologists call a slip slope, which is what geologists call an area of land surrounded by the bend of a meandering river. The fish died there while glass was still raining down from the sky: solidified droplets of molten rock, so-called tektites, which the asteroid impact had thrown into space 3000 kilometers further south. Since this sputum only takes regarding fifteen to thirty minutes to fall back to earth, the fish must indeed have died on the very day and hour that the Mesozoic and dinosaur eras ended.
Telltale bones
But the fish of Tanis contain even more information, thanks in part to their bone structure, which fluctuates with the rhythm of the seasons. Already in December 2021 published Robert DePalma together with other researchers from England and the USA in “Scientific Reports” morphological investigations and isotope analyzes of the fish bones. Accordingly, the animals must all have died together in the northern hemisphere spring or summer.
