Mass Extinctions, Comet Impacts, and The Galaxy

Abstract

AbstractThe hypothesis relating mass extinctions of life on Earth to impacts of comets whose flux is partly modulated by the dynamics of the Milky Way Galaxy contains a number of postulates that can be tested by geologic evidence and statistical analyses. In an increasing number of cases, geologic evidence for impact (widespread impact debris and/or large impact craters) is found at times of mass extinction events, and the record of dated impact craters has been found to show a significant correlation with mass extinctions. Statistical analyses suggest that mass extinction events exhibit a periodic component of about 26 to 30 Myr, and periodicities of 30± 0.5 Myr and 35 ±2 Myr have been extracted from sets of well-dated impact craters. The evidence is consistent with periodic or quasi-periodic showers of impactors, probably Oort Cloud comets, with an approximately 30-Myr cycle. The best explanation for these proposed quasi-periodic comet showers involves the Sun’s vertical oscillation through the galactic disk, which may have a similar cycle time between crossings of the galactic plane.