Curiously the dwarf planet 2003 EL61 shows signs of a major collision in
the last 100 million years. Its surface, and its collision debris
family, all show relatively fresh ice - they're in the Kuiper Belt and
over the billennia cosmic-rays should change the colour of their
water/methane ices to pinkish. Thus something smashed into the parent
body, spun off a moon and a bunch of cometoids, and who knows what else
sometime in the Cretaceous...
...if a piece slammed into Earth I wouldn't be surprised. The remnant of
the parent body has a football like shape due to its very high spin, so
something smacked it very hard. And something else had to careen across
the Kuiper Belt to hit it in the first place.
Adam
PS Isn't there stronger evidence for volcanism playing a role in the K/T
extinction now? I remember a science story about the timing of a flood
basalt province or some such.