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Even a Nobel Prize does not begin to do justice to the full breadth of the astonishing career of Luis Alvarez, who died of cancer in 1988 at the age of 77. Walter brought samples of the Gubbio finding back to Berkeley and showed them to his father, winner of the 1968 Nobel Prize in Physics for his contributions to elementary particle physics. Luis (left) and Walter Alvarez at the K-T Boundary in Gubbio, Italy 1981 (Photo from Berkeley Lab archives) The clay layer itself contained no foram fossils at all. Above the clay layer, in the Tertiary limestone, however, only the fossils of a single species of foram could be seen. Immediately below this clay boundary, the Cretaceous limestone was heavily populated with a wide mix of the fossils of tiny marine creatures called foraminifera, or “foram” for short. Walter Alvarez found that forming a distinct boundary between the limestone of the two periods was a thin layer of red clay. This time span is sometimes referred to as “the Great Dying,” because a massive extinction claimed nearly 75 percent of all the species of life on our planet, including in addition to the dinosaurs, most types of plants and many types of microscopic organisms.
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The limestone rock outside of Gubbio, which was once below the sea, provides a complete geological record of the end of the Cretaceous period and the beginning of the Tertiary period. The story begins in 1977 in Gubbio, Italy, a tiny village halfway between Rome and Florence, where geologist Walter Alvarez was collecting samples of limestone rock for a paleomagnetism study. With the panel’s report in Science having generated a flurry of stories in the media, it seems like a good time to take a look back at how the Alvarez asteroid theory came to be. This cataclysm effectively ended the reign of the dinosaurs and opened the door for the ascension of mammals. The impact delivered a destructive blast thousands of times more powerful than the combined yield of all the world’s nuclear weapons, setting off earthquakes greater than 11 in magnitude and widespread tsunamis, and shrouding the globe for years in a thick cocoon of sky-blackening dust and debris. The theory holds that an asteroid the size of San Francisco, traveling faster than a bullet, slammed into Earth 65 million years ago. The panel ruled in favor of the asteroid, a theory first put forth in 1980 by one of Berkeley Lab’s greatest scientists, the late Nobel laureate Luis Alvarez, and his son Walter, a geologist with UC Berkeley. In the Maedition of the journal Science, an international panel of 41 experts in geology, paleontology and other related fields, after an exhaustive review of the data, declared an end to a 30 year controversy over what triggered the extinction of the dinosaurs – an asteroid or volcanoes. An international panel found in favor of a theory by Luis and Walter Alvarez that an asteroid impact with Earth 65 million years ago triggered the mass extinction of the dinosaurs.