Impact winter

An impact winter is a hypothesized period of prolonged cold climate due to an impact event upon the Earth's planetary surface by a large asteroid or comet. If such meteors were to survive atmospheric entry and successfully impact land or a shallow body of water, it would eject an enormous amount of debris, dust, ash and other particulate materials into Earth's atmosphere, blocking off irradiance from the Sun. This would lead to global dimming and cause the climatic temperature to decrease drastically. If an asteroid or comet with the diameter of about 5 km (3.1 mi) or more were to hit in a deep body of water or explode mid-air before hitting the surface, there would still be an enormous amount of debris released into the atmosphere.

It has been proposed that the rapid climate shifts associated with impact winters could cause severe floral disruptions and subsequently cascadingcollapse of food chains, leading to mass extinctions of the Earth's biosphere that wipe out many of the world's extant species. An example of such an event would be the Cretaceous–Paleogene extinction event, which probably involved a worldwide impact winter caused by the 10 km (6.2 mi) diameter Chicxulub impactor, and led to extinction of nearly all tetrapods weighing more than 25 kilograms (55 lb), which included all non-avian dinosaurs, pterosaurs and Mesozoic marine reptiles.