Impact cratering and the Oort cloud

TL;DR

This paper models comet flux from the Oort cloud due to Galactic tides and molecular cloud encounters, linking impact events to mass extinctions and Earth's biological history over the past 250 million years.

Contribution

It provides a theoretical framework connecting Galactic phenomena with Earth's impact history and suggests a low dark matter density in the Galactic disc.

Findings

Periodic bombardment episodes occur every 25-35 Myr.

Impact cratering record shows a ~36 Myr periodicity.

Galactic plane crossing correlates with increased impact events.

Abstract

We calculate the expected flux profile of comets into the planetary system from the Oort cloud arising from Galactic tides and encounters with molecular clouds. We find that both periodic and sporadic bombardment episodes, with amplitudes an order of magnitude above background, occur on characteristic timescales ~25-35 Myr. Bombardment episodes occurring preferentially during spiral arm crossings may be responsible both for mass extinctions of life and the transfer of viable microorganisms from the bombarded Earth into the disturbing nebulae. Good agreement is found between the theoretical expectations and the age distribution of large, well-dated terrestrial impact craters of the past 250 million years. A weak periodicity of ~36 Myr in the cratering record is consistent with the Sun's recent passage through the Galactic plane, and implies a central plane density ~0.15 M_Sun pc^(-3). This leaves little room for a significant dark matter component in the disc.