[hennie pennie]

Interesting theory here.

[blam]

Clube and Napier published an excellent book in 1990 that details much of this already:

Cosmic Winter

Professor BILL NAPIER is an astronomer at the Armagh Observatory in Northern Ireland and an honorary professor at the Institute for Astrobiology of Cardiff University. He is interested in the relationship between life and the Universe and is a leading authority on the celestial hazard issue. He has co-authored three scientific books and about eighty research papers.

[blam]

See this:

Comet Theory Collides With Clovis Research, May Explain Disappearance of Ancient People