Giant comets and mass extinctions of life: Looking at the crater record

Abstract

I find evidence for clustering in age of well-dated impact craters over the last 500 Myr. At least nine impact episodes are identified, with durations whose upper limits are set by the dating accuracy of the craters. Their amplitudes and frequency are inconsistent with an origin in asteroid breakups or Oort cloud disturbances, but are consistent with the arrival and disintegration in near-Earth orbits of rare, giant comets, mainly in transit from the Centaur population into the Jupiter family and Encke regions. About 1 in 10 Centaurs in Chiron-like orbits enter Earth-crossing epochs, usually repeatedly, each such epoch being generally of a few thousand years' duration. On time-scales of geological interest, debris from their breakup may increase the mass of the near-Earth interplanetary environment by two or three orders of magnitude, yielding repeated episodes of bombardment and stratospheric dusting. I find a strong correlation between these bombardment episodes and major biostratigraphic and geological boundaries, and propose that episodes of extinction are most effectively driven by prolonged encounters with meteoroid streams during bombardment episodes. Possible mechanisms are discussed.

Comment: As Napier writes in his conclusion, "positive evidence for such [bombardment] episodes appears in the impact cratering record. They are found to be tightly correlated with substantial marine extinctions at the level of genera. ... it is suggested here that prolonged atmospheric perturbations arising from fireball storms and dusting are the most energy-efficient means of collapsing food chains, yielding both marine and land extinctions."

See also: Track this: Unseen 'dark comets' may pose threat to Earth