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In this mass extinction, many commonly recognized groups such as non-avian dinosaurs, plesiosaurs and mosasaurs, as well as many other lesser-known groups, died out. The cause of the extinction is most commonly linked to an asteroid about 10 to 15 kilometres (6.2 to 9.3 mi) wide [4] [5] colliding with Earth, ending the Cretaceous.
A conference dedicated to the end-Cretaceous extinction event was held at Utah's Snowbird Ski resort. [45] Alexopoulos and others compared quartz grains from rocks that had been subjected to various types of geologic forces like bolide impact, volcanism, or tectonic deformation with quartz from the K–T boundary layer.
The proposed Shiva crater and other possible impact craters along with the Chicxulub crater have led to the hypothesis that multiple impacts caused the massive extinction event at the end of the Cretaceous period. Chatterjee is confident that Shiva was one of many impacts, stating that "the K-T extinction was definitely a multiple-impact scenario."
But the end-Cretaceous extinction is the only one reliably associated with an asteroid, according to Benton. ... The causes of these extinctions are varied — land-use change, habitat loss ...
The end-Cretaceous event is the only mass extinction definitively known to be associated with an impact, and other large extraterrestrial impacts, such as the Manicouagan Reservoir impact, do not coincide with any noticeable extinction events. [249]
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 main evidence for the Alvarez hypothesis that the Chicxulub impact resulted in the Cretaceous–Paleogene extinction event, supported by earth sciences consensus, [9] comes from the presence around the world of shocked quartz granules, glass spherules and tektites embedded in a layer of clay with extremely high levels of iridium, all signs ...
The end-Cretaceous mass extinction removed the non-avian dinosaurs and made it possible for mammals to expand into the large terrestrial vertebrate niches. The dinosaurs themselves had been beneficiaries of a previous mass extinction, the end-Triassic, which eliminated most of their chief rivals, the crurotarsans.