Born: 13 May 1888, Denmark
Died: 21 February 1993
Country most active: Denmark
Also known as: NA
The following is excerpted from Infinite Women founder Allison Tyra’s book The View from the Hill: Women Who Made Their Mark After 40.
While a 1929 earthquake did lead Danish seismologist Inge Lehmann to theorize (correctly) about the structure of the Earth’s core, it wasn’t a stroke of brilliance that simply popped into her brain. Born in 1888, she completed a mathematics degree at the University of Copenhagen in 1920, where she also took courses in chemistry, physics, and astronomy. She went on to work in geology and seismology for years before the 1929 earthquake on the other side of the world, near New Zealand. By this time, she was familiar with variations in seismographs, which record shock waves and how those waves move differently when traveling through different materials. She realized that “knowledge of the earth’s interior composition could be obtained from the observations of the seismographs”—a way to see into the planet.
Thanks to her background in mathematics and experiences with interpreting seismographs, Lehmann was able to deduce that the center of the earth consisted of a solid inner core, surrounded by a liquid outer layer. The previous theory—only a liquid core—didn’t match the readings, which indicated the waves were bouncing off something solid. She published her hypothesis in 1936, but it wasn’t confirmed until 1970 following the development of more sensitive seismographs. Fortunately, she did live to see this, as Lehmann survived to the age of 104. She had published dozens of papers and served as the chief of Gradmaaling’s seismological department until she retired in 1953—not that she stopped researching simply because she retired. Her last work, a manuscript called “Seismology in the days of old,” was published in 1987, the year she turned 99.
Lehmann was awarded the Gold Medal of the Danish Academy of Sciences and Letters in 1965. The boundary between the liquid and solid layers of the core is named the Lehmann discontinuity in her honor. In 1971, the year after her theory was confirmed, she received the American Geophysical Union’s highest honor, the William Bowie medal. She was described as “the master of a black art for which no amount of computerizing is likely to be a complete substitute.”