1901
Copenhagen, Denmark
Inge Lehmann at the age of 13.
1932
Copenhagen, Denmark
Inge Lehmann in 1932.
Inge Lehmann was a member of the Royal Society.
educator geophysicist scientist seismologist
Inge Lehmann was born on May 13, 1888, in Copenhagen, Denmark to the family of Alfred Georg Ludvik Lehmann, a psychology professor, and, Ida Sophie Tørsleff, a housewife. Both parents came from prominent families. She also had a sister Harriet.
Lehmann was schooled at a private coeducational school called Fællesskolen – which translates as a shared school. The school was new: it had been founded when Inge was 5 years old by Hanna Adler, a wealthy woman. Hanna Adler’s new school was unusual in that boys and girls were treated identically, studying the same subjects and taking part in the same sports and activities. The children were not disciplined as rigorously as in other schools of that time. Inge Lehmann enjoyed her time at the Fællesskolen, but she was sometimes bored because she did not feel challenged enough by the schoolwork.
In 1906, at age 18, Lehmann passed the entrance examination for Copenhagen University with a first rank mark. She started freshman courses in mathematics, chemistry, and physics at Copenhagen University in 1907. She finally graduated in 1920. It took her an exceptionally long time to get a degree: in 1911 she returned to Copenhagen completely burned out after a year at Newnham College, Cambridge. She abandoned her degree to do actuarial work for an insurance company. In 1918, she returned to Copenhagen University, graduating with a mathematics degree in 1920, age 32.
Lehmann continued studying mathematics at the University of Hamburg during the fall of 1922, before taking another position as an actuarial assistant in 1923, this time working with a professor in the actuarial science department at the University of Copenhagen.
Lehmann was captivated by her new academic field and, in 1928, age 40, she obtained a Master of Science degree in geodesy (the science of making measurements related to planet Earth).
In 1923, Inge Lehmann began working as an assistant in Copenhagen University’s actuarial department. In 1925, she became an assistant to the head of the Royal Danish Geodetic Institute, and part of her work involved setting up Denmark’s first seismic stations near Copenhagen, as well as in Ivigtut and Scoresbysund (now Ittoqqortoomiit), Greenland. Because of her growing interest in that topic, she again enrolled in the University of Copenhagen and studied seismology during the summer of 1927, later graduating with a magister scientiarum (master of science) in 1928. That same year Lehmann was appointed as the state geodesist and was made the head of the Seismological Department of the Royal Danish Geodetic Institute. She held the latter post until her retirement in 1953.
The bulk of Lehmann’s work at the Seismological Department involved managing the seismological stations both in Denmark and in Greenland, as well as collecting seismograph information and creating the bulletins associated with the stations. She became interested in determining the location of earthquake epicenters more accurately from the data her seismographs provided. She did so by correlating the primary seismic waveforms collected. She was also interested in calculating the travel times of various types of seismic waves through the planet.
P and S waves travel through the planet Earth after an earthquake. Scientists studying the waves produced by earthquakes learned that Earth's core has separate liquid and solid layers. S waves do not travel through liquid, but P waves do. A simplified diagram shows the S waves on the left and the P waves on the right, but waves of both types would actually radiate in all directions.
In 1929, while examining seismograph data collected after a large earthquake in New Zealand, Lehmann noticed that seismographs stationed in the Russian cities of Swerdlowsk (Yekaterinburg) and Irkutsk collected seismic waves with amplitudes that were higher than she had expected. She also discovered that some waves traveling away from the earthquake’s focus appeared to have been "bent." It was known at the time that Earth’s core deflected secondary (S) waves and some primary (P) waves - thereby creating shadow zones behind the core - as those waves traveled outward from an earthquake’s focus to its antipode on the other side of the planet. In 1936, Lehmann published her findings in a paper that posited a three-shelled model of Earth’s interior (which was made up of the mantle, outer core, and inner core), with seismic waves traveling through each shell at different but constant velocities. The model included Earth’s core but also postulated the existence of an inner core. It was not until 1970 that advances in seismographs provided unequivocal evidence of the inner core’s existence. The boundary between the inner and outer core, which occurs at a depth of roughly 5,100 km (about 3,200 miles), is known as the Lehmann discontinuity.
Lehmann is also known for researching Earth’s mantle. Working with American seismologist Beno Gutenberg in 1954, she noticed the existence of a region in Earth’s upper mantle in which seismic waves travel faster. That region, which spans perhaps 50 km (about 31 miles) and is also known as the Lehmann discontinuity, occurs about 200 km (120 miles) below Earth’s surface.
Inge Lehmann is famous for her discovery of the inner core of Earth. In addition to her discoveries, Lehmann co-founded the Danish Geophysical Society (1936) and chaired the organization in 1941 and 1944. She was awarded the William Bowie Medal of the American Geophysical Union in 1971 for her contributions in the field of geophysics and received the Medal of the Seismological Society of America in 1977. The American Geophysical Union created the Inge Lehmann Medal in her honor in 1995, and, starting in 1997, it was awarded to researchers displaying "outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core." Two boundary regions, or discontinuities, are named for her: one Lehmann discontinuity occurs between Earth’s inner and outer core at a depth of roughly 5,100 km (about 3,200 miles), and the other occurs at a depth of approximately 200 km (about 120 miles) beneath Earth’s surface in the upper mantle.
Inge Lehmann didn't seem to be very religious but the place of her burial suggests that she was baptized Lutheran.
Inge Lehmann was not involved in politics and was completely immersed into science.
Although Oldham had discovered Earth’s metallic core, seismologists still did not completely understand the meaning of the data recorded at their observatories. Lehmann and other workers were puzzled about the behavior of the P-waves. Earthquake data from observatories showed these were not traveling through Earth in the way they were expected to. They were appearing in locations they ought not to. Lehmann had an idea. People believed that Earth, below its solid crust, was molten. She wondered if the planet’s inner core might actually be solid. If it were solid, surrounded by molten liquid that would account for the odd behavior of the P-waves.
Lehmann developed mathematical models of our planet featuring a solid inner core and found out that such a planet agreed with the observed data. Lehmann was able to conclude that P-waves were appearing in unexpected locations because they were being refracted and reflected to these locations by the boundary between the Earth’s solid inner core and liquid outer core. The inner core, she calculated, had a radius of about 1400 km. Lehmann published her findings in 1936, in a paper entitled very simply P.’
Within a few years, Lehmann's new model of Earth’s inner structure had been generally although not universally accepted by the scientific community. With the passage of time, as ever more accurate seismic measurements were taken confirming Lehmann’s work, the solid core became accepted in full.
Inge Lehmann was a member of the Royal Society and the Danish Geophysical Society.
Inge Lehmann was a very shy girl, who did not enjoy being in the spotlight. She continued to be shy throughout her long life. Her interests were not restricted to science. She was concerned with the poor in her native Denmark and the plight of European refugees. Travel in conjunction with her work also afforded her frequent opportunities to pursue two of her hobbies - visiting art galleries throughout Europe and the United States, and the outdoors. Lehmann enjoyed hiking, mountain climbing, and skiing.
Inge Lehmann didn't marry and never had a family of her own.
