Birch, A. Francis (earth scientist)


(1903-1992) American Geophysicist

Francis Birch is famous not only for his contributions to geophysics and geology but also to the World War II effort in his role in development of the atomic bomb. He is considered one of a few founders of the science of solid Earth geophysics. His most famous research was to determine the basic architecture of the deep Earth. In a 1952 paper entitled “Elasticity and the Constitution of the Earth’s Interior,” he conclusively showed that the mantle of the Earth is mainly composed of silicate minerals and that the upper mantle and lower mantle regions are each basically homogenous but of different composition. The two regions are separated by a thin transition zone associated with silicate phase transitions from open structured minerals in the upper mantle to denser, closed structured minerals in the lower mantle. Birch also showed that the inner and outer cores are alloys of crystalline and molten iron respectively. This breakthrough remains a benchmark in Earth science that appears in every textbook in physical geology.

Francis Birch combined theory with experimental practices in his research. His geological research was combined with the disciplines of physics and electrical engineering. By combining these three disciplines, Birch was able to successfully solve many virtually otherwise unaddress-able geologic problems. He had the uncanny ability to recognize a geologic problem, decide an approach to the problem, and use that approach to find a result to the problem. Birch’s research dealt with elasticity, phase relations, thermal properties, and the composition of the Earth’s interior as summarized in his paper “Elasticity and the Earth’s Interior.” He knew that there was a limited amount of data regarding high-pressure physical properties of rocks and minerals. These had to be addressed in order to better interpret measurements made by seismological and gravity techniques. To these ends, Birch’s experimental research concentrated on elasticity, phase relations, thermal properties and heat flow, and the composition of the Earth’s interior. His laboratory studies of seismic wave velocities in rocks and their variation with pressure and temperature discovered the first approximations of density-pressure relationships at high compressions. Birch used these data that he collected to interpret global seismic data in regard to composition and structure of the interior.

Another major contribution Birch and his research team made was to our knowledge of terrestrial heat flow. By combining experimental data on thermal conductivities of rocks with temperature gradient measurements from boreholes and tunnels, they helped distinguish heat flow as one of the most important conditions of continental geophysics. This work is presented in several major papers, including “Heat from Radioactivity” and “Heat Flow in the United States.”

Albert Francis Birch was born in Washington, D.C., on August 22, 1903, where he spent his youth. He graduated from Western High School in 1920. He attended Harvard University and participated in the ROTC program. He graduated magna cum laude in 1924 with a bachelor of science degree in electrical engineering. He worked for two years for the New York Telephone Company in engineering when he decided to change his course of study to physics. Birch received an American Field Service Fellowship that led to two years of study (1926-1928) at the Institut de Physique, University of Strasbourg, France. Birch studied under Pierre Weiss who was one of the founders of modern magnetism. As a result, Birch decided to return to Harvard in 1928 as a graduate student in physics. He worked in the high-pressure laboratory of Percy W. Bridgman who received the Nobel Prize in physics in 1946. Birch was an instructor and tutor in physics from 1930 to 1932. He received his master of science degree in 1929 and his Ph.D. in 1932.

Just prior to graduation, Harvard University offered Birch the opportunity to work in the newly established high-pressure research program as the first research associate in geophysics. The next year, he became director of the program. It was at this time that Francis Birch married Barbara Channing; they had three children. Francis Birch took a leave of absence in 1942 to participate in the World War II effort. He began at the Radiation Laboratory at Massachusetts Institute of Technology, but in 1943 he accepted a commission as a second lieutenant in the U.S. Navy at the Bureau of Ships in Washington, D.C. This assignment was short-lived because he was quickly chosen by Robert Oppenheimer to participate in the Manhattan Project. He moved to Los Alamos, New Mexico, where he was soon promoted to commander and the head of the Uranium-235 fission bomb project (code name Little Boy). Birch personally supervised the assembly and loading of “Little Boy” onto the B-29 Enola Gay prior to the bombing of Hiroshima, Japan. Francis Birch was awarded the Legion of Merit by the U.S. Navy for these outstanding efforts.

Francis Birch returned to Harvard University in 1945 to resume his academic career. He quickly advanced to become the prestigious Sturgis Hooper professor of geology in 1949 and later he would be the chairman of the Geological Sciences Department. He retired to professor emeritus in 1974, but continued his research at a bit slower pace until his death on January 30, 1992, at 88 years old.

Francis Birch led an extremely productive career serving as author of numerous scientific articles in international journals and professional volumes. Many of these papers are benchmark studies in mantle structure and processes, heat flow, and the propagation of seismic waves through the Earth. In recognition of his numerous contributions to Earth sciences, Francis Birch received numerous prestigious honors and awards. He was a member of the National Academy of Sciences. He received honorary doctoral degrees from the University of Chicago and Harvard University. He also received the National Medal of Science from President Johnson in 1968. He was recipient of the Gold Medal from the Royal Astronomical Society of London in 1973, the Vetlesen Medal for 1960, both the Arthur L. Day Medal in 1950 and the Penrose Medal in 1969 from the Geological Society of America, the William Bowie Medal from the American Geophysical Union in 1960, and the Bridgman Medal from the International Association for the Advancement of High Pressure Research in 1983.

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