In July 1994, we became aware of the threat posed by cosmic interlopers when comet Shoemaker-Levy 9 explosively smashed into the planet Jupiter. The question on everyone's mind was clear: Could something like this ever happen to the Earth? Unequivocably the answer is yes. In fact, it is believed that such an impact occured 65 million years ago, resulting in the death of the dinosaurs.

Learn about the many global threats to life on the Earth, from the danger of giant asteroids striking our fragile planet, to the effect of chlorofluorocarbons on our atmosphere, to the prospects of a nuclear "winter". Look through alien eyes to consider each risk and how together we can work to save our world.