Francis Birch (geophysicist)
Encyclopedia
Albert Francis Birch was an American geophysicist best known for his experimental work on the properties of Earth-forming minerals at high pressure and temperature, in 1952 he published a well-known paper in the Journal of Geophysical Research
,
where he demonstrated that the mantle
is chiefly composed of silicate minerals
, the upper and lower mantle are separated by a thin transition zone associated with silicate phase transitions, and the inner and outer core are alloys of crystalline and molten iron
. The most famous portion of the paper, however, is a humorous footnote he included in the introduction:
During World War II
he took a leave of absence from Harvard and was assigned to the Manhattan Project
, first in New York City, then in New Mexico. Because of his knowledge of metals and metallurgy he was in charge of designing and engineering the triggering mechanism for the Hiroshima atomic bomb code-named Little Boy
; and went to Tinian to supervise loading it onto Enola Gay
(the Boeing B-29 Superfortress tasked with dropping the bomb) and assembling the bomb before takeoff. He devised the 'double plug' system that allowed for actually arming the bomb after Enola Gay took off (so that if it crashed, there would not be a nuclear explosion on Tinian).
In 1947, he adapted the isothermal Murnaghan equation of state, which had been developed for infinitesimal strain, for Eulerian finite strain, developing what is now known as the Birch-Murnaghan equation of state
.
In 1961, Birch published two papers
on compressional wave velocities establishing a linear relation (now called Birch's law) of the compressional wave velocity Vp of rocks and minerals of a constant average atomic weight
with density 
as:
.
Birch was the Sturgis Hooper Professor of Geology at Harvard University
from 1949 to 1974. He served as the president of the Geological Society of America
in 1963-1964 and he received numerous honors in his career, including the GSA's Arthur L. Day Medal
(1950) and Penrose Medal
(1969), the American Geophysical Union's
William Bowie Medal
(1960), the National Medal of Science
(1967), the Vetlesen Prize
(1968) (shared with Sir Edward Bullard
), the Gold Medal of the Royal Astronomical Society
(1973), and the International Association for the Advancement of High Pressure Research's Bridgman Medal (1983). Since 1992, the AGU's Tectonophysics
section has sponsored a Francis Birch Lecture, given at its annual meeting by a noted researcher in this field.
Journal of Geophysical Research
The Journal of Geophysical Research is a peer-reviewed scientific journal published by the American Geophysical Union 80 times per year. It contains original research on the physical, chemical, and biological processes that contribute to the understanding of the Earth, Sun, and solar system...
,
where he demonstrated that the mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
is chiefly composed of silicate minerals
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
, the upper and lower mantle are separated by a thin transition zone associated with silicate phase transitions, and the inner and outer core are alloys of crystalline and molten iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
. The most famous portion of the paper, however, is a humorous footnote he included in the introduction:
"Unwary readers should take warning that ordinary language undergoes modification to a high-pressure form when applied to the interior of the Earth. A few examples of equivalents follow:"
High Pressure Form Ordinary Meaning Certain Dubious Undoubtedly Perhaps Positive proof Vague suggestion Unanswerable argument Trivial objection Pure iron Uncertain mixture of all the elements
During World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
he took a leave of absence from Harvard and was assigned to the Manhattan Project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
, first in New York City, then in New Mexico. Because of his knowledge of metals and metallurgy he was in charge of designing and engineering the triggering mechanism for the Hiroshima atomic bomb code-named Little Boy
Little Boy
"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...
; and went to Tinian to supervise loading it onto Enola Gay
Enola Gay
Enola Gay is a Boeing B-29 Superfortress bomber, named after Enola Gay Tibbets, mother of the pilot, then-Colonel Paul Tibbets. On August 6, 1945, during the final stages of World War II, it became the first aircraft to drop an atomic bomb as a weapon of war...
(the Boeing B-29 Superfortress tasked with dropping the bomb) and assembling the bomb before takeoff. He devised the 'double plug' system that allowed for actually arming the bomb after Enola Gay took off (so that if it crashed, there would not be a nuclear explosion on Tinian).
In 1947, he adapted the isothermal Murnaghan equation of state, which had been developed for infinitesimal strain, for Eulerian finite strain, developing what is now known as the Birch-Murnaghan equation of state
Birch-Murnaghan equation of state
In continuum mechanics, an equation of state suitable for modeling solids is naturally rather different from the ideal gas law. A solid has a certain equilibrium volume V_0, and the energy increases quadratically as volume is increased or decreased a small amount from that value...
.
In 1961, Birch published two papers
on compressional wave velocities establishing a linear relation (now called Birch's law) of the compressional wave velocity Vp of rocks and minerals of a constant average atomic weight
Atomic weight
Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12...
with density as:.Birch was the Sturgis Hooper Professor of Geology at Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
from 1949 to 1974. He served as the president of the Geological Society of America
Geological Society of America
The Geological Society of America is a nonprofit organization dedicated to the advancement of the geosciences. The society was founded in New York in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hitchcock, John R. Proctor and Edward Orton and has been headquartered at 3300 Penrose...
in 1963-1964 and he received numerous honors in his career, including the GSA's Arthur L. Day Medal
Arthur L. Day Medal
The Arthur L. Day Medal is a prize awarded by the Geological Society of America, established in 1948 by Arthur Louis Day for "outstanding distinction in contributing to geologic knowledge through the application of physics and chemistry to the solution of geologic problems"....
(1950) and Penrose Medal
Penrose Medal
The Penrose Medal was created in 1927 by R.A.F. Penrose, Jr. as the top prize awarded by the Geological Society of America to those who advance the study of geoscience.-Award winners:* 2011 Paul F. Hoffman* 2010 Eric J. Essene* 2009 B. Clark Burchfiel...
(1969), the American Geophysical Union's
American Geophysical Union
The American Geophysical Union is a nonprofit organization of geophysicists, consisting of over 50,000 members from over 135 countries. AGU's activities are focused on the organization and dissemination of scientific information in the interdisciplinary and international field of geophysics...
William Bowie Medal
William Bowie Medal
The William Bowie Medal is awarded annually by the American Geophysical Union for 'outstanding contributions to fundamental geophysics and for unselfish cooperation in research"...
(1960), the National Medal of Science
National Medal of Science
The National Medal of Science is an honor bestowed by the President of the United States to individuals in science and engineering who have made important contributions to the advancement of knowledge in the fields of behavioral and social sciences, biology, chemistry, engineering, mathematics and...
(1967), the Vetlesen Prize
Vetlesen Prize
The Vetlesen Prize is awarded from Columbia University's Lamont-Doherty Earth Observatory and the G. Unger Vetlesen Foundation.-Background:The Vetlesen Prize has been described as an attempt to establish an equivalent of a Nobel award for geophysics or geology...
(1968) (shared with Sir Edward Bullard
Edward Bullard
Sir Edward "Teddy" Crisp Bullard FRS was a geophysicist who is considered, along with Maurice Ewing, to have founded the discipline of marine geophysics...
), the Gold Medal of the Royal Astronomical Society
Gold Medal of the Royal Astronomical Society
-History:In the early years, more than one medal was often awarded in a year, but by 1833 only one medal was being awarded per year. This caused a problem when Neptune was discovered in 1846, because many felt an award should jointly be made to John Couch Adams and Urbain Le Verrier...
(1973), and the International Association for the Advancement of High Pressure Research's Bridgman Medal (1983). Since 1992, the AGU's Tectonophysics
Tectonophysics
Tectonophysics, a branch of geophysics, is the study of the physical processes that underlie tectonic deformation. The field encompasses the spatial patterns of stress, strain, and differing rheologies in the lithosphere and asthenosphere of the Earth; and the relationships between these patterns...
section has sponsored a Francis Birch Lecture, given at its annual meeting by a noted researcher in this field.