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The results of this study, which were based on estimated real global biodiversity, showed that between 628 and 1,078 non-avian dinosaur species were alive at the end of the Cretaceous and underwent sudden extinction after the Cretaceous–Paleogene extinction event. [136]
Walter Alvarez at the original site where he discovered the dinosaur extinction evidence near Gubbio, Italy. Alvarez and his father Luis W. Alvarez, together with Frank Asaro and Helen Michel, discovered that a clay layer occurring right at the Cretaceous–Paleogene (K-Pg) boundary was highly enriched in the element iridium.
Luis Walter Alvarez, left, and his son Walter, right, at the K–T Boundary in Gubbio, Italy, 1981. The Alvarez hypothesis posits that the mass extinction of the non-avian dinosaurs and many other living things during the Cretaceous–Paleogene extinction event was caused by the impact of a large asteroid on the Earth.
The study confirmed previous findings that identified the asteroid as a carbonaceous-type, or C-type, asteroid, but refuted a 2021 hypothesis that the dinosaur killer was likely a comet.
The study shows that the asteroid, while having a severe initial impact, did not immediately kill off the dinosaurs - instead slowly killing them off over a few years.
Around 66 million years ago, an asteroid larger than Mt. Everest ripped through the atmosphere of Earth, striking our planet at the Yucatán Peninsula, on the southeastern coast of Mexico.
A rebuttal in Astronomy & Geophysics countered that Loeb et al. had ignored that the amount of iridium deposited around the globe, 2.0 × 10 8 –2.8 × 10 8 kg (4.4 × 10 8 –6.2 × 10 8 lb), was too large for a comet of the size implied by the crater, and that they had overestimated likely comet impact rates.
[1] An impact winter is a hypothesized period of prolonged cold weather due to the impact of a large asteroid or comet on the Earth's surface. If an asteroid were to strike land or a shallow body of water, it would eject an enormous amount of dust, ash, and other material into the atmosphere, blocking the radiation from the Sun. This would ...