Maybe there was a belch of hydrogen sulfide involved in the Permian extinctions. However, did it leave some geological trace, as did the vast Siberian outpourings of magma, both on land and in the sea, over the course of a million years during the period?

Stan Skirvin
Scottsdale, Ariz

The ocean venting proposed by Lee Kump’s group at Pennsylvania State University doesn’t refute that major volcanic eruptions contributed to the Permian extinction. The two phenomena could have combined their lethal effects. Some geologic evidence exists for ocean venting, such as fossil signs that hydrogen sulfide–producing bacteria lived unusually close to the surface in the Permian ocean. However, no direct evidence for high atmospheric concentrations of hydrogen sulfide gas has yet been found .—N. Moreira