Slide 1

Inge Lehmann was, as she referred to herself, the only Danish seismologist. By the time began to study seismology, the scientific model of the earth had changed dramatically. Building on many discoveries in a period of only 30 years, seismologists now believed that the Earth had a thin outer layer known as the crust, a liquid mantle separated from the crust by the Mohorovicic discontinuity, and a core.

In 1929, an earthquake occurred on the other side of the planet: in New Zealand. However, seismic waves once again did not behave as predicted. Due to the discontinuities in the Earth, there are "shadow zones," where seismic waves do not arrive after an earthquake. Figure 1 illustrates these shadow zones for both P- and S-waves.

Figure 1. Taken from https://www.amnh.org/learn-teach/curriculum-collections/earth-inside-and-out/inge-lehmann-discoverer-of-the-earth-s-inner-core

In 1936, Lehmann proposed the solution to this puzzle: the Earth's core was made of a liquid outer layer and a solid inner core. Her findings were confirmed in 1970 and today the boundary between the outer core and the inner core is known as the Lehmann discontinuity in her honor.