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:
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Fascinating.
I remember when I was in high school making a model of the earth for science class. I used an old damaged basketball and cut a pie slice out of it so we would see the inner structure. Adding paper mache and poster paint I came up with something very much like the Lehmann version above.
Now I know whom to thank for the design (and it wasn’t a deity).
My mother worked in banking back in the 70’s and 80’s. She trained many of her male bosses.
During the war my mother helped her boss who couldn’t read a ruler.
This is really interesting, and I am glad to learn of a woman scientist who has shown us significant features of the earth.
Some things about the inner core (because these things make me look things up for fun): The inner core is thought to be mostly an iron-nickle alloy, but it is also enriched with heavier metals like gold and platinum and onward. The inner core was once thought to be a single crystal, but it is now known to contain several discontinuities, so it is not a single structure but is instead rather lumpy with regional differences in density.
The inner core is growing, since the liquid outer core is gradually cooling and solidifying onto the inner core. It is possible that the earth did not have a solid inner core as recently as 2 billion years ago.
I also looked this up as I wondered what the solid inner core was made of (if any different from NiFe). Per Wikipedia:
Because the inner core is denser (12.8 ~ 13.1)g⁄cm³ than pure iron or nickel at Earth’s inner core pressures, the inner core must contain a great amount of heavy elements with only a small amount of light elements, mainly Si with traces of O. Based on such density a study calculated that the core contains enough gold, platinum and other siderophile elements that if extracted and poured onto the Earth’s surface it would cover the entire Earth with a coating 0.45 m (1.5 feet) deep.
What would happen if we could tap into that and extract as much gold or platinum as we wanted? An impossible feat for sure, but it makes you wonder why and how humans place monetary value on shiny metals based on rarity in the earth’s crust. Just another man-made illusion…we’re really good at that.
1) As you pointed out, we can’t get to it.
2) Most people aren’t / weren’t aware of the enormous amounts of precious metals in the Earth’s inner core.
3) Though some precious metals have certainly been considered valuable throughout history for mostly aesthetic reasons, every one of them is also highly valuable for practical reasons in our modern technological world.
Another interesting tidbit about the cores of planets, there are serious hypotheses that indicate that the cores of certain size ranges of gas giants could be composed of diamond! Though I don’t know how they have fared over time.
A real heroine of science! She was the only woman in a recent series about famous Danish scientists on national Danish TV (archived here: http://videnskabsfolk.dk/ ) –alas, only in Danish.
What is nice is the way the programmes were made: The presenter (Johan Olsen; himself a biochemist & the lead singer in a Danish rock band) asking questions to the scientists (well, ok, dressed-up actors), who then responds with actual quotes from their papers, letters, biographies, etc.
I love the quote about competing with incompetent men in vain. I’m sure many women can still relate.
Great stuff – I wasn’t aware of her before.
There’s an interesting page on seismic waves at http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html
which I believe is at an intro level, if anyone’s interested. It has (about 3/4 of the way down) a very nice graphic of how waves propagate through the earth.
Also note the turning a bad-thing to a good-thing – a productive use of nuclear weapons testing!
Nice point.
Prior to the work of Lehman, William Thomson, aka Lord Kelvin, was able to use his scientific authority to form a consensus, one that only began to unravel in the early 1890s, that the earth was solid all the way through. The view supporting a liquid inner region, although it predated the idea of heating by radioactivity, seems (despite lava flow of volcanoes) to have only dawned slowly in the early 20th century.
Thomson was a very religious man and may have constructed his model of the inner earth with the intent to produce measurements that would ‘prove’ the earth, since its formation, had been cooling for only millions and not billions of years. This would make the slow process of biological evolution as proposed by Charles Darwin impossible and place himself and physics on the right and righteous side, that of Intelligent Design.
Misspelled “Lehmann” – apologies.
It is nice to see women scientists noted for their contributions. It took a lot of courage for women to enter into science in our all too recent past. I still recall being told by a teacher that Marie Currie got credit for her husband’s work – she had not made any contribution to science. That is in the 1960s – I am very happy – as a scientist and a woman – to see the change.
Lots of cities in Denmark have discovered that streets are mostly named after men, and have decided to do something about it.
So here I am, at work, in a new office building on Inge Lehmanns gade (street).
How nice!