Related References Keith Didn't Mention
Here are some articles I think have more detailed info than Keith's overview.
http://www.planetary.org/html/news/articlearchive/headlines/2000/Panspermia.htm
http://www.planetary.org/html/news/articlearchive/headlines/2000/swappingrocks.html
For those that have read them before, it might be worth rereading in the context of Keith's overview.
No implication of plagiarism intended in title Keith. Just think these are links worth posting relevant to your article.
Regards,
Mark
