Dear Stales: thanks for the link, which I will have to study. One more question. There have been a number of studies on very large methane hydrate deposits on seafloor reported on Internet. When I saw map of Chicxulub crater on Yucatan extended well out into Gulf of Mexico, it occurred to me that a very large amount of sea floor methane hydrate could have been vaporized and ignited, contributing a very large amount of energy to the impact. I sent an e-mail to scientist studying the crater, and he replied that the idea was new to him. I subsequently found one site not written by a scientist mentioning the possibility of methane hydrate having been ignited. It seems to me that methane hydrate might also have produced a large amount of soot that could have blocked sunlight, contributing to long winter and extinctions Please comment.