Did a comet kill...

the great mammoths, and perhaps also lead to the disintegration of the Clovis culture in North America?

That's certainly one of the leading hypotheses regarding the extinction of the dinosaurs about 65 million years ago, and the same mechanism may have caused a similar, but considerably younger, dying event about 13,000 years ago on this continent.

While an iridium anomaly has been found to stratigraphically mark the Cretaceous/Tertiary boundary that coincides with the demise of the dinosaurs, the discovery of a layer of nanodiamonds in strata approximately 12,900 years old is also suggestive of a cometary impact. These microscopic diamond particles can only be created under high pressure and vaporizing conditions, hence the speculation that another fragmenting bolide may be responsible. However, there is no evidence of a crater of the right age, leading some scientists to speculate that the impact may have been an air burst phenomenon, or have taken place over a thick portion of an ice sheet.

I tell you, those falling space rocks will eventually get us all. Until then, don't worry, be happy.

UPDATE: An opposing study