The disappearance of the dinosaurs 65 million years ago has become one of the most gripping scientific whodunits of all time. Dinosaurs were not the only victims of this mass destruction; they are only the most conspicuous to strike our imaginations. Many other animals were eradicated at the same time, for example, the beautiful, spiral-shelled ammonite mollusks. Flowering plants also were decimated, to be replaced for a while by ferns. Many explanations of this mysterious holocaust were proposed, until, in 1978, the American physicist and Nobelist Luis Alvarez, together with his son Walter and other coworkers, made a remarkable observation. They found that a thin layer of sedimentary rocks deposited at the time of the extinction was twenty times richer in the rare element iridium than the adjoining layers. Iridium is more abundant in cosmic material than on Earth, and the workers had measured it in order to time the rate at which the material that witnessed the great extinction was deposited at the bottom of the ancient seas. If sedimentation had been fast, the material would have included less cosmic dust, that is, less iridium. The opposite would be true if sedimentation had been slow. The investigators were looking for modest changes; they had not bargained for the huge increase they found. Here is one more example of serendipity, the magic mother of many a scientific discovery, a fairy that cannot be courted but sometimes gratuitously favors those who search for truth, even if they do so with the wrong idea in mind. If you urgently need admission essay writing, buy customized writing at our site! But one must be able to recognize such a blessing. As the great Louis Pasteur once said, chance favors only the prepared mind.

In the present case, the gift from chance could hardly be missed. The scientists could think of only one explanation for the iridium anomaly: A huge asteroid, six or more miles in diameter, fell on our planet 65 million years ago. First received with considerable skepticism, this suggestion is now widely accepted. Corroborative evidence has been found in many parts of the world, and the probable impact area, almost two hundred miles wide, has been located at a site, Chicxulub, on the north coast of the Yucatan Peninsula in Mexico.

How could such an event, a mere prick on the skin of the Earth, cause such a worldwide catastrophe? By sheer brute force. It is estimated that the impact released the equivalent of 100 million megatons of energy, or as much as 10,000 times the energy that would be released by all the atomic bombs of the world exploding at the same time! Clouds of dust, smoke, and soot obscured the sun for years. Raging fires destroyed plant and animal life over large parts of the continents. A period of piercing cold (impact winter) was followed by intense warming due to the greenhouse effect of released gases. Acid rain poisoned the waters. Against this doomsday scene, the biblical picture pales to insignificance and the warnings of ecologists become derisory