A big rock came from space and fell down, and went Booooooom!!!!!!!!!

The event appears to have hit all continents at the same time. Dinosaurs, for example, are known from the Maastrichtian of North America, Europe, Asia, Africa, South America and Antarctica,^[21]but are unknown from the Cenozoic anywhere in the world. Similarly, fossil pollen show devastation of the plant communities in areas as far apart as New Mexico, Alaska, China, and New Zealand.^[13]

Even though the boundary event was severe, there was significant variability in the rate of extinction between and within different clades. Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked sunlight and reduced the solar energy reaching the Earth's surface. This plant extinction caused a major reshuffling of the dominant plant groups.^[22]Omnivores, insectivores and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources. No purely herbivorous or carnivorous mammals seem to have survived. Rather, the surviving mammals and birds fed on insects, worms, and snails, which in turn fed on dead plant and animal matter. Scientists hypothesize that these organisms survived the collapse of plant-based food chains because they fed on detritus (non-living organic material).^[23][24][25]

In stream communities few animal groups became extinct because stream communities rely less directly on food from living plants and more on detritus that washes in from land, buffering them from extinction.^[26] Similar, but more complex patterns have been found in the oceans. Extinction was more severe among animals living in the water column than among animals living on or in the sea floor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton while animals living on or in the ocean floor feed on detritus or can switch to detritus feeding.^[23] Coccolithophorids and molluscs (including ammonites, rudists, freshwater snails and mussels), and those organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, it is thought that ammonites were the principal food of mosasaurs, a group of giant marine reptiles that became extinct at the boundary.^[27] The largest air-breathing survivors of the event, crocodyliforms and champsosaurs, were semi-aquatic and had access to detritus. Modern crocodilians can live as scavengers and can survive for months without food, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms or fragments of organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous.^[24]

After the K–Pg extinction event, biodiversity required substantial time to recover, despite the existence of abundant vacant ecological niches.^[23]