Lehmann, Inge (1888-1993), a Danish geodesist and seismologist, became the first scientist to show that Earth has a solid inner core. Geodesy is the study of Earth’s size, shape, and gravitational field. Seismology is the study of seismic waves ( shock waves ) produced by earthquakes or explosions. Seismologists study these waves to learn about earthquakes and about the structure of Earth’s interior.
Lehmann was born on May 13, 1888, in Copenhagen , Denmark . Unlike many students in Europe or the United States at the time, she attended a school where girls were given the same educational opportunities as boys. Lehmann went on to study mathematics at the University of Copenhagen and at Cambridge University in the United Kingdom. In 1911, she returned to Copenhagen, where she worked in an actuarial office, a place where mathematics is used to establish estimates of risk. Lehmann resumed her studies in 1918 at the University of Copenhagen, where she received a master’s degree in mathematics in 1920. She did further studies in Hamburg, Germany, without completing a degree. In 1923, she took a job as an assistant in actuarial science at the University of Copenhagen.
Lehmann’s interest in seismology began in 1925, when she assisted in setting up seismological research stations in Denmark and Greenland. In 1927, she traveled to various European countries to study under leading seismologists. She received a degree in geodesy in 1928 from the University of Copenhagen. She then became chief of the seismological department at the Danish Geodetic Institute in Copenhagen. In the same year, she was appointed Denmark’s state geodesist.
In 1929, Lehmann analyzed the seismic data from an earthquake that occurred in New Zealand. She observed that certain pressure waves generated by earthquakes, called P waves, were reflected in a pattern that could only occur if Earth had a solid core at its center. Scientists at the time believed Earth had a core of liquid, surrounded by the mantle and solid crust. Lehmann published her findings in 1936 and received international acclaim for her discovery.
Lehmann retired from the Danish Geodetic Institute in 1953 but remained active in seismology. Later research with more sensitive seismographs has shown that Earth has an inner core made mostly of solid iron and nickel . It is about 1,500 miles (2,400 kilometers) across, one-fifth the diameter of the entire planet. Lehmann died on Feb. 21, 1993, in Copenhagen. In 1997, the American Geophysical Union established the Inge Lehmann Medal in her honor. The medal is awarded to scientists who greatly advance our knowledge of Earth’s interior.
