Today’s animated Google doodle celebrates the 127th birthday of Inge Lehmann. Most of you, like me, won’t know who she is, but Google is trying to bring to our attention accomplished but unsung women scientists. Lehmann (1888-1993; she lived to 104!) should certainly be of note, for she discovered the nature of the Earth’s core. As Wikipedia notes:
Inge Lehmann (ForMemRS; May 13, 1888 – February 21, 1993) was a Danish seismologist and geophysicist who discovered the Earth’s inner core.In 1936, she postulated from existing seismic data the existence of an inner core with physical properties distinct from the outer core’s and that Earth’s core is not a single molten sphere. Seismologists, who had not been able to propose a workable hypothesis for the observation that the P-wave created by earthquakes slowed down when it reached certain areas of the inner Earth, quickly accepted her conclusion.
Vox has a great explanation of how she used fast seismic waves (P waves) to discover that, contrary to what people thought, the Earth wasn’t just a mass of rock surrounding a fully molten core, but that the core itself had a solid inner nucleus:
Over the next few years, she closely analyzed this and other data sets. In the pre-digital age,her cousin later recalled, Lehmann would record the data on pieces of cardboard torn from boxes of oatmeal, and sometimes sat surrounded by them in her garden, puzzling over the numbers. Eventually, she had an idea: a solid inner core inside the soft, molten outer core, which would reflect some P-waves, causing them to end up in the shadow zone.
Her subsequent calculations, published in a 1936 paper simply titled P’ (as P-waves were then called), confirmed that the idea. “I then placed a smaller core inside the first core and let the velocity in it be larger so that a reflection would occur when the rays through the larger core met it,” she wrote, years later. “The existence of a small solid core in the innermost part of the earth was seen to result in waves emerging at distances where it had not been possible to predict their presence.”
And she lived long enough to do this as well:
In her later years, she used seismological data on underground nuclear explosions to discover another, subtler discontinuity in the upper mantle, at roughly 136 miles below the surface. Scientists still don’t fully understand this boundary, now called the Lehmann discontinuity.
She faced the usual barriers to women in science, and even in the 1950s they wouldn’t appoint her as a professor in Copenhagen. As Time Magazine notes:
Lehmann was educated at a progressive school that valued equal treatment between genders. But when her professional career took off she often faced discrimination for being a woman, once being quoted as saying, “You should know how many incompetent men I had to compete with — in vain.”
Click on the screenshot below to see the animation: