Supernovas are terribly important for the... the world because the giant star of large mass, 10 times, 20 times the mass of the sun, has made all these heavy elements, not only the ones I mentioned, but all others as well, and the supernova now ejects all these elements into the galaxy and they are then in the galaxy ready to form new stars. And it is, well, a star like the sun which is a little less than 5 billion years old, is much younger than the galaxy which may be about 10 billion years old, and so the sun when it was formed, collected all that material which had been made by the supernova. Now, I should be still clearer; not all the elements are made in the supernova itself, but the... the material which is made in the supernova, which is mainly iron-56 and silicon, sulfur. That material then can go into another big star and in that other big star the temperature gets warm enough so that neutrons are produced just thermally by temperature, and these neutrons then gradually add themselves to existing nuclei and in that way you get the rich variety of... of nuclei which we see in the universe. As I said, it's this way that elements are produced, and it is nice to look back to 1938 when the main thing that Gamow and Weizsäcker wanted was to build up the elements. Time was not ripe for that. Time was ripe at that time only to explain the energy from stars, and later on astrophysicists, Schwarzschild, Iben, recognized that high temperatures would be formed after hydrogen is exhausted. Salpeter came along and made carbon; Hoyle came along and made oxygen; and then the other astrophysicists showed how other elements are made; then we get the supernova and then from the material of the supernova then other stars can make all the very rich variety of elements and isotopes which we find in the world.