Decline in extinction rates and scale invariance in the fossil record

We show that the decline in the extinction rate during the Phanerozoic can be accurately described by a logarithmic fit to the cumulative total extinc tion. This implies that extinction intensity is hiring off approximately as the reciprocal of time. We demonstrate that this observation alone is suff icient to explain the existence of the proposed power-law forms in the dist ribution of the sizes of extinction events and in the power spectrum of Pha nerozoic extinction, results that previously have been explained by appeari ng to self-organized critical theories of evolutionary dynamics.