It was noted by my very good friend Luis Alvarez and his son who made the original approach. A meteorite of ten miles or more in diameter that hit sixty-five million years ago in the Caribbean. It is practically certain by now that it was the cause of the extermination of the dinosaurs. It is estimated that as a consequence not only of the impact but of the dust it stirred up and the exclusion of the sunlight for a long period of time, at least 90% of the living beings were killed and something like 70% of the genera, of the kinds of living beings, was exterminated. Indeed, that event marks the division between the Mesozoic and the Cenozoic period, the biological middle ages of the Earth and the biological recent ages of the Earth. People analyzing the history of life on Earth used to believe in relatively slow transitions from one period of the ancient Earth into the next. Now there is a spe- suspicion that some, or maybe all, of these changes have been due to impacts by meteorites of great sizes. Now of course it so happens that for us humans that was a fortunate event; the dinosaurs were gone, a period followed that for reasons that we do not understand completely, although do we- we do understand it in part, many mutations, our ancestors very small animals changed in all kinds of forms of which the latest, and I may modestly say, ourselves, are the most recent product.