Power spectra of extinction in the fossil record

Recent Fourier analyses of fossil extinction data have indicated that the p ower spectrum of extinction during the Phanerozoic may take the form of 1/f noise, a result which, it has been suggested, could be indicative of the p resence of 'critical dynamics' in the processes giving rise to extinction. In this paper we examine extinction power spectra in some detail, using fam ily-level data from two widely available compilations. We find that althoug h the average form of the power spectrum roughly obeys the 1/f lay the spec trum can be represented more accurately by dividing it into two regimes: a low-frequency one which is well fit by an exponential, and a high-frequency one in which it follows a power law with a 1/f(2) form. We give explanatio ns for the occurrence of each of these behaviours and for the position of t he crossover between them.