CONSIDERING THE CASE FOR BIODIVERSITY CYCLES: REEXAMINING THE EVIDENCE FOR PERIODICITY IN THE FOSSIL RECORD

We re-examine the evidence for a 62 Myr periodicity in observed marine animal biodiversity throughout the Phanerozoic identified by Rohde and Muller; we also consider whether periodicity is present in origination and extinction. Our analysis uses the Lomb-Scargle Fourier Transform, which does not require evenly spaced samples and is not effected by zero padding of the data. Diversity data were also partitioned in various ways to determine the resiliency of periodicity. The 62 Myr periodicity in biodiversity is statistically robust and is primarily caused by fluctuations occurring between roughly 520 Ma and 150 Ma. We found that origination and extinction intensity may be affected by an artifact at 27 Myr in the duration of stratigraphic intervals. Nevertheless, when a procedure free of this artifact is implemented, the 27 Myr periodicity appears in origination, suggesting that the artifact may be ultimately based upon a real signal in the data; the duration closely matches the cyclicity identified by Raup and Sepkoski. A 62 Myr feature appears in extinction when this same procedure is used. We conclude that evidence for periodicity at 62 Myr is robust, while evidence for periodicity at approximately 27 Myr is also present, albeit more ambiguous; these results lend further support to the notion that one or more large scale cycles may have profoundly influenced the history of life. The 62 Myr periodicity may have been mediated by an astrophysical mechanism. In particular, the period and phase of the 62 Myr fossil biodiversity cycle and the known motion of the Solar System perpendicular to the plane of the Galactic disk closely coincide. Times of displacement to Galactic north correspond to lows of fossil biodiversity. The causal factor could be cosmic rays generated at a galactic termination/bow shock; cosmic rays could influence life on this planet through their documented biological and climatic affects.