Patterns of family extinction depend on definition and geological timescale

The recent claim 1 of an approximate 26-Myr periodicity in the pattern of mass species extinction over the past 250 Myr has already stimulated much astrophysical speculation and debate on causal mechanisms 2–13 . However, as shown here, the evidence for that claim is strongly contingent on arbitrary decisions concerning the absolute dating of stratigraphical boundaries 14 , the culling of the database and the definition of what is mass extinction as opposed to background extinction. This evidence becomes insufficient under other plausible geological timescales and other acceptable definitions of mass extinction. Analysis of the nonculled database shows that the reliability of identification of mass extinctions and their timing is at present extremely limited. It also suggests that the apparent periodicity of mass extinctions results from stochastic processes.