While working one day on an unrelated goal, a geochemist named Walter Alvarez discovered what seemed to be a peculiar layer of clay that looked out of place. The layer was only about two centimeters thick, and had a laminated look to it. He also noticed that above and below the layer, there were fossils called ammonites. Ammonites being fossils formed from tiny oceanic organisms millions of years ago. It was very strange that in this particular two-inch layer of clay, it seemed the usually prevalent ammonites were not present. Peter Ward states what would later become the significance of these ammonites when he says, "So we've got ammonites, ammonites, ammonites. And then everything goes extinct. The fact that they all went extinct in one thin layer indicates this is one of the great catastrophes of the world. They lived over three hundred million years up to this point. They'd weathered everything the world had ever thrown at them. And bang. (Ward, http://www.bbc.co.uk/science/horizon/spacecratertran.shtml).
Alvarez did not immediately come to this conclusion. He would later look into this aberration, and discover that the clay contained the very rare element iridium. It turns out that this element was turning up in copious amounts all over the world. This did not seem to make sense to Alvarez due to the extreme sparseness of the element. He took his information to this father, Louis, a very well respected, Nobel physicist. Together they formulated what would become the basis of the catastrophe theory.
Although remarkably uncommon, the element iridium was often seen in un-earthly objects, or better said, "You don't find these very rare elements such as iridium in very large quantities in the earth's crust, but they are very common in certain types of primitive meteorites. And those types of meteorites we believe are characteristic of large asteroids, and even comets that could slam into the earth" (Sharpton, http://www.
