Giant comets and mass extinctions of life

TL;DR

This paper presents evidence linking giant comet impacts to multiple mass extinction events over the last 500 million years, suggesting that comet disintegration episodes caused repeated bombardments affecting Earth's biosphere.

Contribution

It introduces the idea that rare, giant comets from the Centaur population caused impact episodes correlated with mass extinctions, a novel explanation beyond asteroid breakups.

Findings

Identification of nine impact episodes over 500 Myr.

Correlation between impact episodes and mass extinctions.

Impact episodes likely caused by disintegrating giant comets.

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.