1981 Essays

Asteroid Extinction Hypothesis

Kent, Dennis V.

A distinguishing feature of the asteroid impact hypothesis presented by Alvarez et al. (6 June, p. 1095) for the end-of-Cretaceous biotic crisis is that it is based on direct physical evidence: the distribution of iridium in several Cretaceous-Tertiary sedimentary sections. I draw attention to other evidence which suggests that (i) a high Ir concentration may not be uniquely associated with an extraordinary extraterrestrial event and (ii) the impact of a large asteroid in any case is not likely to have had the dire consequences to life on the earth that they propose.