When I discussed the possibility of an asteroid heading toward the earth I didn’t discuss the end result if the object was not stopped from impacting the earth. This is in part because I just don’t know enough about the physics involved. However I can recommend that you read Lucifer’s Hammer by Larry Niven and Jerry Pournell (IIRC), I do remember the title if you care to search it on http://www.amazon.com/ , to get a vision of what might happen (though the object in this book is a bit larger than the one I posit…) if we are struck by an asteroid.
I believe it is sufficient to say that such a strike would change the face of the earth enough to possibly eliminate the human race (though in truth people are as tough as cockroaches) and definitely would probably lead to the extinction of some of the life forms we know today.
© 2010 Vic Jones