Another more interesting example of a famous scientist working in the fields other than his expertise was Luis W. Alvarez. Luis W. Alvarez was awarded the Nobel Prize in Physics in 1968. However, he was better known or was more famous, especially to the general public, in the field of paleontology (古生物学). In 1980, Alvarez hypothesized that an asteroid approximately 10 km in size struck the earth some 65 million years ago, creating a huge explosion, lofting a cloud of debris and dust into the atmosphere, and severely blocking sunlight that suppressed photosynthesis and drastically lowered the global surface temperature. As a result, dinosaurs and many other species became extinct. Alvarez's hypothesis or theory created a shock in the field of paleontology because, if it were correct, it would have solved the biggest puzzle in paleontology. At the time, paleontology was considered to be a well-established science field with a sound theoretical foundation of Darwin's theory of evolution. There existed many different hypotheses and a few well established theories that solved the biggest problem of dinosaur extinction within the field of paleontology. On the other hand, Alvarez was considered as an outsider. At the time, it was really unthinkable that an outsider suddenly came to the field and gave the solution to a long-standing difficult problem in the field of paleontology. As a result, Alvarez immediately received many criticisms from other paleontologists. However, it turned out that Alvarez's hypothesis can explain all the major aspects of the dinosaur extinction. Most importantly, the theory contains a predictive clue of an anomalously rich iridium layer in the earth's crust that can be tested and verified. Alvarez's theory of explaining the extinction of dinosaurs 65 million years ago after more than 100 million years of domination on the earth is now well accepted by the science community.
Since we have discussed the topic of global warming extensively on this forum, let me also mention here one old hypothesis (before Alvarez's hypothesis) on the extinction of dinosaurs that was related to the global warming. Geological evidence indicated that the earth's surface temperature rose significantly toward the end of the Cretaceous period (白垩纪). It was also known in biological studies that mammals' testicle (睾丸) functioned normally only in a narrow range of temperature. Because of a large ratio of body weight to body surface of the dinosaurs, which makes the dissipation of body heat extremely slow, a worldwide rise in temperature at the end of the Cretaceous period (about 65 million years ago) caused the testicle of dinosaurs to stop functioning and led to their extinction by sterilization of male dinosaurs. The major difficulty or the key logical hole of this hypothesis was that it failed to explain the extinction and the patterns of the extinction of many other species across a wide range of habitats, from terrestrial to marine, which happened simultaneously with the dinosaur extinction. There was no such difficulty in Alvarez's theory.
Below was the paper that proposed the catastrophic hypothesis of the dinosaur extinction:
Alvarez, L. W., Alvarez, W., F. Asaro, and H. V. Michel, 1980: Extraterrestrial cause for the Cretaceous-Tertiary Extinction. Science, 208, 1095-1108.
The second author Walter Alvarez, a geologist, was the son of Luis Alvarez. Hence, this work was also considered a good example of father-son team work in science community.
Alvarez's theory on dinosaur extinction also had a significant impact on the field of atmospheric sciences. Since 1950s, various environmental effects on weather and climate changes following nuclear explosions, including the one caused by a significant reduction of solar radiation due to the debris clouds from the explosions, were investigated by the atmospheric science community. Alvarez's work injected new insights into the field, reinvigorated the research by focusing on a full nuclear exchange corresponding to an all-out atomic war, and alerted the general public on a severe consequence of a "nuclear winter" that would have the same effect as the one that caused the dinosaur extinction.