2 links
Extinctions: Cycles of Life and Death Through Time
park.org
Covers patterns and periodicity of extinction, with discussions of major mass extinctions and minor extinction events.
The Late Devonian Mass Extinction
lpi.usra.edu
A professional technical paper discussing whether the Late Devonian (Frasnian-Famennian) mass extinction was initiated by an extraterrestrial impact or an earth-bound event.