Source: Adapted and updated from Hallam and Wignall (1997, 248).

Source: Adapted and updated from Hallam and Wignall (1997, 248).

lion by volume, a level one thousand times higher than during the worst air pollution episodes in modern cities (Prinn and Fegley 1987), and capable of poisoning any animals and plants exposed directly to the atmosphere. The nitric oxide would also destroy the ozone layer, exposing the already decimated flora and fauna to a flood of ultraviolet radiation. Nitrogen oxides would react with water to produce large amounts of nitric acid, which in turn would cause superacid rain with a pH of around 1.0 (see also Retallack 2004; and for a counter argument, Maruoka and Koeberl 2003). Rain of that acidity would destroy much of the biosphere. Great quantities of carbon dioxide, and possibly noxious chemicals, would also enter the atmosphere. Plumes from oceanic impacts would contain shock-heated steam, as well as rock in various states. Initially, the plume would rush, at ultra supersonic speeds, into the hole punched in the atmosphere by the bolide, and would catch up with the bow shock wave to which it would impart extra power. The plume would carry much material into the stratosphere. Large particles would fall out rapidly, but a cloud of fine dust would spread around the world. The dust cloud would stay in suspension for months or years, blocking out sunlight (Toon et al. 1982), although aerosols might have caused the darkness and not dust (Pope 2002). The darkness would lead to a reduction or

Figure 7.4 Speculative flow diagram linking large-body impacts to mass extinctions. Source: After Huggett (1997a), inspired by Stothers and Rampino (1990).
Table 7.3 Catalogue of destruction following a large bolide impact at Chicxulub at the Cretaceous-Tertiary boundary.

Time after impact



1 second

Annihilation of about 30,000 km2

Hildebrand et al. (1995)

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