There have been numerous articles in Eos and elsewhere recently that discuss the cause of the mass extinctions at the Cretaceous-Tertiary (K-T) boundary. Clark Chapman's interesting article on the Snowbird II meeting (“Snowbird II: Global Catastrophes,” Eos, April 4, p. 217) is one of the latest. I suppose that few geoscientists would quarrel with his principal conclusion that an association has now been established between the extinctions and the impact of large meteorites, although many paleontologists remain troubled by the inability of a single extraterrestrial impact to account for the complexities of the longdrawn-out extinctions of the various species.

My main concern, as an igneous penologist, is the omission by Chapman of any significant reference to the Deccan basalt eruptions, the most frequently suggested alternative cause of the climatic changes that produced the extinctions [Officer and Drake, 1985]. This is now known to have been an extraordinary volcanic event, both in its rate of eruption and in its total volume. Furthermore, the eruptions occurred, as closely as radiometric techniques can define, exactly at the K-T boundary. Barring an unlikely coincidence, these eruptions, unique in the last 100 m.y., must surely be related to the equally exceptional worldwide extinctions. This suggestion may be seen as an unwelcome complication to an otherwise satisfactory explanation for the extinctions. Yet, if we accept Chapman's conclusion that the extinctions are probably the result of meteorite impact, then we should also accept, at least as a working hypothesis, that meteorite impact, continental flood basalt eruptions, and the extinctions are interconnected [Alt et al., 1988; Basu et al., 1988].