Could the break-up of a giant comet have given rise to recurring legends about fire from the skies - could it also have destroyed civilizations and plunged Europe into the Dark Ages? The theory is being taken increasingly seriously by scientists and it is now known that the impact of a comet 65 million years ago in the Yucatan Peninsula of Mexico triggered the catastrophe that led to the extinction of the dinosaurs.;But what exactly are comets, and where do they come from? This book reveals that these cosmic missiles have been a continuing problem throughout geological time. It examines the controversial claims that there are "periodic extinctions" of life on earth linked to a recurring cycle of cometary impacts and the authors come to a frightening conclusion about the future of humankind on earth. The next appalling series of cosmic hits will almost certainly lead to the extinction of humankind - unless knowledge has advanced enough by then to both find and neutralize a comet heading our way.