Radar, Iridium, and the K/T Impact: A Career Dedicated to Scientific Discovery.

Greetings. Scientific discoveries. The uncovering of previously unknown occurrences. The eternal search for knowledge about anything and everything. Those are reasons enough, in my opinion, to keep one's mental faculties squarely focused on the acquisition of new information and the opportunities for learning such content offers.

We now come to Luis Walter Alvarez (June 13th of 1911 – September 1st of 1988,) an experimental physicist, inventor, and professor who was awarded the Nobel Prize in Physics back in 1968 for his discovery of resonance states in particle physics using the hydrogen bubble chamber. The American Journal of Physics commented, in 2007, that "Luis Alvarez was one of the most brilliant and productive experimental physicists of the twentieth century." Agreed!

Luis Alvarez earned a Ph.D. in 1936 from the University of Chicago, and soon went to work for Ernest Lawrence at the Radiation Laboratory at the University of California at Berkeley. Alvarez devised a set of experiments to observe K-electron capture in radioactive nuclei, predicted by the beta decay theory but never before directly observed. He also produced tritium using the cyclotron and measured its lifetime. In collaboration with Felix Bloch, he measured the magnetic moment of the neutron. Alvarez was a busy man, and that is selling him well short. 

By 1940, Alvarez had joined the MIT Radiation Laboratory, where he contributed to a number of World War II radar projects, from early improvements to Identification Friend or Foe (IFF) radar beacons, nowadays referred to as transponders, to a system known as VIXEN for preventing enemy submarines from determining that they had been located by the new airborne microwave radar technologies. The radar system for which Alvarez is best-known and which has played a major role in all subsequent aviation, most particularly in the post-war Berlin airlift, was Ground Controlled Approach (GCA.) 

Notably, Alvarez spent a few months at the University of Chicago working on nuclear reactors for Enrico Fermi before coming to Los Alamos to work for J. Robert Oppenheimer on the Manhattan Project. Alvarez worked on the design of explosive lenses, and the development of exploding-bridgewire detonators. As a member of Project Alberta, he observed the Trinity nuclear test from a B-29 Superfortress, and later the bombing of Hiroshima from the B-29 The Great Artiste. Talk about historical anecdotal observations from a qualified observer. 

After the war Alvarez was heavily involved in the design of a liquid hydrogen bubble chamber that allowed his team to take millions of photographs of particle interactions, develop complex computer systems to measure and analyze these interactions, and discover entire families of new particles and resonance states. This is the scientific research work that resulted in his being awarded the Nobel Prize in 1968. 

In 1980 Luis Alvarez and his son, geologist Walter Alvarez, along with nuclear chemists Frank Asaro and Helen Michel, "uncovered a calamity that literally shook the Earth and is one of the great discoveries about Earth's history." The calamity they spoke of is the Cretaceous/Paleogene extinction event, the most recent of the mass extinctions that have occurred in the long history of complex life on Earth, perhaps the worst single day in the history of the planet, 66 million years ago. 

Stepping back a few years, in the 1970s, Walter Alvarez was conducting geologic research in central Italy. During the course of his endeavors, he had located an outcrop on the walls of a gorge whose limestone layers included strata both above and below the geologic layer marking the boundary between the Cretaceous and Paleocene Periods. What caught Alvarez's eye was the fact that a thin layer of unidentified clay was located precisely at the aforementioned boundary. Walter informed his father that the unexplained layer of clay marked the boundary where the non-avian dinosaurs and much of the Cretaceous fauna became extinct, an extinction event that was still unexplained at the time.

Luis Alvarez had access to the nuclear chemists at the Lawrence Berkeley Laboratory in California, and was able to work with the previously mentioned Frank Asaro and Helen Michel, who used the technique of neutron activation analysis to meticulously study the anomalous clay. By 1980, Luis Alvarez, his son Walter Alvarez, Asaro, and Michel published a seminal scientific paper proposing an extraterrestrial cause for the Cretaceous/Paleogene extinction event. In the years following the initial publication of their article, the anomalous clay was also found to contain soot, glassy spherules, shocked quartz crystals, microscopic diamonds, and rare minerals formed only under conditions of extreme temperature and immense pressure, adding additional support for the extraterrestrial impact explanation. 

Publication of the scientific paper brought a substantial amount of criticism from the geologic community, and a heated scientific debate was soon underway. After Luis Alvarez's death in 1988, irrefutable evidence was found of a massive impact crater off the coast of the Yucatán peninsula in Mexico, the Chicxulub impact crater, which provided strong support for the Alvarez's impact hypothesis. Years and decades later, researchers have found that the extinction of the non-avian dinosaurs may have occurred over thousands of years, rather than millions of years as had previously been assumed, with such a time frame being a blink of an eye in geologic terms. 

While alternative extinction hypotheses have been offered, including overwhelming volcanism at the Deccan Traps, the impact crater theory remains dominant among geologists and paleontologists. Recent discoveries have suggested that some of the non-avian dinosaurs may have managed to survive into the Paleocene, but with such low numbers and scattered representation that they eventually joined their Cretaceous peers, and expired into oblivion. The discussion of the Cretaceous/Paleogene extinction event, its ramifications for today's biosphere, and for our own species' existence, was all made possible by the inquisitive mind of the late, great Luis Walter Alvarez. We all owe him a debt of scientific gratitude. 

Rest well good Sir.

Thank you for your time and consideration.