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None of the other major mass extinctions from the last 540 million years are associated with signatures of asteroid impact like widespread shocked quartz ejecta or iridium spikes. The end-Cretaceous extinction event was by no means the most destructive, its just the last spike on this graph the fraction of genera going extinct at any given time.
http://upload.wikimedia.org/wikipedia/commons/thumb/0/06/Extinction_intensity.svg/400px-Extinction_intensity.svg.png
I'm impressed instead by the theory that most mass extinctions are climate events initiated by flood basalts and massive C02 injections. Subsequent effects include catastrophic global warming, liberation of seabed methanes, ocean stratification, anoxia and photic-zone euxinia (permitting sulfur-reducing bacteria to live near surface), releases of H2S, destruction of the ozone layer, and massive dieoff of land genera, and tremendous erosion. More or less in that order. Peter Ward summarizes this here, and there's increasing evidence from molecular biomarkers like isorenieratene, which is only produced in extinction scenarios like this one.
So, the chance that all of your descendants will die in an asteroid impact seems to be less than thought a decade ago, when paleontologists and geologists were busy scouring all mass extinction horizons for signs of impacts. No, the fruits of life will die in a slower, more insidious and painful manner.
― Derelict, Monday, 8 March 2010 16:30 (fourteen years ago) link