You posted a few links a while ago about proof that a comet hit Egypt during the time of the exodus.I didn't. There's an old topic (I think it was Blam's) from a few years back, "Moses' Comet", but that didn't pertain to a comet hitting the Earth, if memory serves. :')
http://www.portal.telegraph.co.uk/news/main.jhtml?xml=/news/2001/11/04/wmet04.xml&sSheet=/news/2001/11/04/ixhomef.html
Meteor clue to end of Middle East civilisations
The catastrophic effect of these could explain the mystery of why so many early cultures went into sudden decline around 2300 BC.