Hi Dan
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...
http://arxiv.org/abs/0804.2864
...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.
Dan Chure wrote:
FYI;
The pdf for this paper is available at
http://www.boulder.swri.edu/~bottke/Reprints/Reprints.html
Supplemental info is available from the Nature website.
Dan