Decline in Extinction Rates and Self-Similarity in the Fossil Record

Recently, it has been shown that the power spectrum of extinction intensity during the Phanerozoic takes a power-law form, which, it is suggested, may indicate the presence of critical phenomena in the dynamics underlying the extinction process. In this paper we reproduce these results using the extensive fossil database compiled by Sepkoski, and show two new results. First, we demonstrate that the exponent of the power law is quite different for the Sepkoski database from the exponent found by previous authors, and second, we show that the power-law form can be explained as a result of the decline in average extinction rate during the Phanerozoic. Thus, there is no need to invoke critical phenomena to explain the observed power spectrum in this case.