(1940- ) American Stratigrapher, Tectonics
Walter Alvarez has been the leader of one of the greatest revolutions in geology, extraterrestrial impacts. He decided to address one of the big questions in geology: what caused the great extinction of the dinosaurs? He chose the most complete section of rock that includes the extinction event, which occurred at the Cretaceous-Tertiary (K-T) boundary about 65 million years ago. The area chosen is in the Umbria region of the northern Appenines, Italy. The unit is a reddish limestone called Scaglia Rossa, which has its most complete section at Gubbio. There Alvarez found a 1-cm thick layer of clay right at the boundary. Across this boundary, fossils record a major extinction event of foraminifera (plankton) and other marine life. Walter Alvarez consulted with his father, Nobel Prize-winning physicist Luis Alvarez, at the University of California at Berkeley, where Walter Alvarez had just taken a position. These two collaborated with two other nuclear chemists in an attempt to determine the amount of time that it took to deposit the layer by measuring the amount of the element iridium, assuming a constant flux of this cosmic dust. Much to their surprise, the layer contained an anomalously high concentration of iridium, far greater than what could be deposited by cosmic influx. This work was released in a landmark paper entitled “Extraterrestrial Cause for the Cretaceous-Tertiary Extinction: Experimental Results and Theoretical Interpretation.” The team analyzed several other sections at Stevns Klint, Denmark, and in New Zealand, and found that this iridium anomaly was worldwide. The team postulated that the collision of an asteroid or comet of 10-km diameter with the Earth could be the culprit. They proposed that the impact produced a huge crater from which an enormous mass of dust was emitted. The dust settled all over the Earth but not before blocking sunlight for a long period of time. The dust cloud inhibited photosynthesis and thus caused a collapse of the food chain from the ground up.
The evidence amassed and the theory quickly evolved after this initial discovery. Over 75 localities have been identified with the K-T iridium anomaly. Enrichment in platinum, osmium, and gold in roughly chondritic proportions was also found in the layer. At other localities, distinctive microspherules (glass melt) have been found as well as shocked quartz, a texture that can only be produced by extreme pressure. Even a potential impact crater called Chixulub has been identified off of the coast of the Yucatan Peninsula in Mexico. There was a tremendous cooling of the atmosphere as recorded in pollen samples and tremendous loss of species as a result of this event.
Walter Alvarez was born on October 3, 1940, in Berkeley, California, where he spent his youth. He attended Carleton College, Minnesota, where he majored in geology. He graduated in 1962 with a bachelor of arts degree. He attended Princeton University, New Jersey, for graduate studies, where his adviser was HARRY H. HESS. He graduated with his doctoral degree in 1967 with the thesis topic “Geology of the Simarua and Carpintero areas, Guajira Peninsula, Colombia.”
He worked in the petroleum industry for several years before joining the Lamont-Doherty Geological Observatory in 1971. He started as a resident scientist (1971—1973) and became a research associate (1973-1977). In 1977, he joined the faculty at University of California at Berkeley where he currently holds the rank of professor.
Walter Alvarez has received numerous awards and honors. He was a Guggenheim Fellow in 1983-1984 and a Fellow of the California Academy of Sciences in 1984. He received the G. K. Gilbert Award of the Geological Society of America in 1985. In 1986, he became an Honorary Foreign Fellow of the European Union of Geosciences as well as a Miller Research Professor at University of California, Berkeley. In 1991, he was elected to the National Academy of Sciences as well as receiving the Rennie Taylor Award of the American Tentative Society for science journalism. He was elected as a foreign member of the Royal Danish Academy of Sciences in 1992 and as a member of the American Academy of Arts and Sciences in 1993. In 1998, he received the Journalism Award of the American Association of Petroleum Geologists.
Walter Alvarez has other interests besides pure scientific research, namely journalism. His book T. Rex and the Crater of Doom (Princeton University Press, 1997) is a prime example of his interest in translating the results of research to works that could be appreciated by the general population. In addition to this popular work, he is an author of numerous scientific articles in international journals and professional volumes. Many of these are seminal works of the Earth sciences.