Inge Lehmann

Inge Lehmann
File:Inge Lehmann 1932.jpg
Born	(1888-05-13)May 13, 1888 Copenhagen, Denmark
Died	February 21, 1993(1993-02-21) (aged 104) Copenhagen, Denmark
Alma mater	University of Copenhagen, University of Cambridge
Awards	William Bowie Medal (1971)
Scientific career
Fields	seismology, geophysics
Institutions	Geodetical Institute of Denmark

Inge Lehmann ForMemRS (May 13, 1888 – February 21, 1993) was a Danish seismologist and geophysicist who discovered the Earth's inner core. In 1936, she postulated from existing seismic data the existence of an inner core with physical properties distinct from the outer core's and that Earth's core is not a single molten sphere. Seismologists, who had not been able to propose a workable hypothesis for the observation that the P-wave created by earthquakes slowed down when it reached certain areas of the inner Earth, quickly accepted her conclusion.

Early life and education

Inge Lehmann was born and grew up in Østerbro, a part of Copenhagen. Her father was experimental psychologist Alfred Georg Ludvik Lehmann (1858–1921). She received her school education at a pedagogically progressive high school led by Hanna Adler, Niels Bohr's aunt. According to Lehmann, her father and Adler were the most significant influences for her intellectual development.

She studied mathematics at the University of Copenhagen and University of Cambridge, interrupted by poor health. She continued her studies of mathematics in Cambridge from 1910-1911 at Newnham College. In 1911, she returned from Cambridge feeling exhausted from the work and put her studies aside for a while. She developed good computational skills in an actuary office she worked in for a few years until she resumed studies at Copenhagen University in 1918. She completed the candidates magisterii degree in physical science and mathematics in two years. When she returned to Denmark in 1923, she accepted a position at Copenhagen University as an assistant to J.F. Steffensen, the professor of actuarial science.

Career

After a few years of work in the insurance business, she became an assistant to the geodesist Niels Erik Nørlund, who assigned her the task of setting up seismological observatories in Denmark and Greenland. The beginning of her interest in seismology dates to this time. In 1928, she passed her exam in geodesy and accepted a position as state geodesist and head of the department of seismology at the Geodetical Institute of Denmark led by Nørlund.

In a paper titled P', Lehmann was the first to interpret P wave arrivals - which inexplicably appeared in the P wave shadow of the Earth's core - as reflections from an inner core. Other leading seismologists of the time, such as Beno Gutenberg, Charles Richter, and Harold Jeffreys, adopted this interpretation within two or three years. World War II and the German occupation hampered Lehmann's work and her international contacts significantly during the following years.

In 1952, Lehmann was considered for a professorship in geophysics at Copenhagen University, but ultimately was not appointed. In 1953, she retired from her position at the Geodetic Institute. She then moved to the USA for several years and collaborated with Maurice Ewing and Frank Press on investigations of Earth's crust and upper mantle. During this work, she discovered another seismic discontinuity, which lies at depths between 190 and 250 km and now bears her name, the Lehmann discontinuity. Francis Birch noted that the "Lehmann discontinuity was discovered through exacting scrutiny of seismic records by a master of a black art for which no amount of computerization is likely to be a complete substitute".

Awards and honors

She received many honors for her outstanding scientific achievements, among them the Gordon Wood Award (1960), the Emil Wiechert Medal (1964), the Gold Medal of the Danish Royal Society of Science and Letters (1965), the Tagea Brandt Rejselegat (1938 and 1967), the election as a Fellow of the Royal Society in 1969, the William Bowie Medal (1971, as the first woman), and the Medal of the Seismological Society of America in 1977. She was awarded honorary doctorates from Columbia University in 1964 and from the University of Copenhagen in 1968, as well as numerous honorific memberships.

The asteroid 5632 was named Ingelehmann in her honor.

In 1997, the American Geophysical Union established the Inge Lehmann Medal to honor "outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core."

On the 127th anniversary of her birth, Google dedicated its worldwide Google Doodle to her.

Key publications

• Lehmann, Inge (1936): P'. Publications du Bureau Central Séismologique International A14(3), S.87-115

See also

• Richard Dixon Oldham
• Lehmann discontinuity
• List of geophysicists

Bibliography

• Lehmann, Inge (1987). "Seismology in the Days of Old". EOS. 68 (3): 33–35.
• Swirles, Lady Jeffreys, Bertha (1994). "Inge Lehmann: Reminiscences". Quarterly Journal of the Royal Astronomical Society. 35 (2): 231. Bibcode:1994QJRAS..35..231W.
• Inge Lehmann in CWP at UCLA
• Royal Society citation
• Inge Lehmann: Discoverer of the Earth's Inner Core
• "WiP: Herstory: Spotlight Scientist: Inge Lehmann". Purdue University. Retrieved 15 October 2013.
• Bolt, Bruce. "Inge Lehmann". UCLA. Retrieved 15 October 2013.