Honoring Inge Lehmann

On May 15th, the University of Copenhagen will hold a symposium celebrating Inge Lehmann. As part of the celebration, a monument honoring her and her discovery will be unveiled on Frue Plads. Frue Plads is a square located just in front of the historical buildings of the University, and the square contains busts of prominent alumni of the university, including several prominent scientists (like Niels Bohr), but not, to my knowledge, any honoring a woman.

So, who is Inge Lehmann, and why is she honored by the University of Copenhagen?

To answer that, let’s go to wikipedia’s entry on her:

Inge Lehmann ForMemRS (13 May 1888 – 21 February 1993) was a Danish seismologist and geophysicist. In 1936, she discovered that the Earth has a solid inner core inside a molten outer core. Before that, seismologists believed Earth’s core to be a single molten sphere, being unable, however, to explain careful measurements of seismic waves from earthquakes, which were inconsistent with the Earth having a single molten core. Lehmann analysed the seismic wave measurements and concluded that Earth must have a solid inner core and a molten outer core to produce seismic waves that matched the measurements. Other seismologists tested and then accepted Lehmann’s explanation. Lehmann was also the longest-lived woman scientist, having lived for over 104 years.

The discovery of the solid inner core was done through the analysis of P-waves, and was published by her in her 1936 paper P’. What she observed was basically that P-waves didn’t get deflected by the (outer) core, as might be expected, but that it deflected on something else, further in, leading her to believe that there was an inner core inside the core. We now talk of the outer core (which is liquid) and the inner core (which is solid).

Her ideas were widely accepted within a few years, but it wasn’t until computers came around, that they could be demonstrated to be true through computer calculations. This happened in 1971.

Inge Lehmann is largely unknown in Denmark outside seismology and geophysics circles, but she is probably one of the most important scientists to ever come out of the country, which can be witnessed through the fact that the American Geophycical Union (AGU) has named a medal after her, awarded for “outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.”

As a side note. When reading up on Lehmann, who I had heard about, but didn’t know too many details about, I noticed that she didn’t finish her study until she was 32, having taken a break for several years, working in an insurance company. I can’t help think about how the current policy of pushing people through their study would have led her to drop out, and thus she would never have had the chance to make her discovery.

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