Heh, those damned comets. Apparently there is a theory that the Great Chicago Fire of 1871 was caused by a comet (link from Slashdot), and not Mrs. O'Leary's kick-happy cow. Which incidentally jives very well with the explanation Matt Groening gives in "Simpsons Tall Tales", where Paul Bunyan saves the earth from a meteor, but finds it too hot to hold onto, and ends up throwing the meteor onto Chicago.