Walter Alvarez is one of the Berkeley scientists responsible for the theory, now well-established, that the dinosaurs perished after a huge asteroid or comet hit the Yucatan Peninsula sixty-five million years ago, setting off a monstrous tsunami and a sequence of disastrous climatic changes. In telling his story, Alvarez explains the way geologists read the earth’s history in rock formations such as those found in the Bottaccione Gorge at Gubbio, Italy.
Establishing the impact theory of dinosaur extinction prompted a shoot-out between the gradualists, who scorn suggestions of sudden violent changes in the earth’s history, and the catastrophists, who emphasize the effects of sudden cataclysms. Alvarez tells this story well.
The discovery of iridium at just the right level in the Gubbio limestone was a crucial step in the impact theory. It suggested a slow accumulation of meteorite dust that would have been consistent with the tremendous and long-lasting shower of geological debris to be expected from a huge impact.
The search for the impact site—which went on for roughly twelve years—finally ended in 1991 with the finding of the Chicxulub crater on the north coast of the Yucatan Peninsula. The fact that the crater overlapped water and land had slowed down its discovery, because impacts on land create different clues from those on water.
The discovery of Chicxulub did much to substantiate the theory that the dinosaurs died out after a great impact clouded the earth’s surface, and Alvarez tells the story clearly. He gives generous credit to his fellow scientists who contributed so much from their highly specialized disciplines.