The end of the world as we know it - Science, News - The Independent

The end of the world as we know it - Science, News - The Independent: "What kind of catastrophe would it take to end the world? Astronomical intruders provide a potentially serious threat. Impacts can be caused by stray rubble from the Asteroid Belt and the rocky snowballs that travel in highly elliptical orbits in the comet cloud. There are many fewer large bits of debris than small bits, so the interval between large impacts is much longer than the interval between small impacts."