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Inge Lehmann: Inside the Earth

Updated: Dec 2, 2023

Hello everyone! I'm Tina and this is Women Weekly, where I post about one wonderful woman in the STEM field every Friday. Today it's going to be about a seismologist who discovered the true form of our planet's core – Inge Lehmann.


Inge Lehmann was born in 1888 in Copenhagen, Denmark. She was a shy and sensitive kid and remained that way throughout adulthood. Inge attended a new progressive private school called Fællesskolen that treated boys and girls equally. She entered Copenhagen University with the highest mark and began studying mathematics, physics, and chemistry. She also studied at the University of Cambridge. Her studies were interrupted two times, the first time because of poor health and the second time because of burnout. She spent a couple of years working as an actuary assistant at an insurance company, before resuming her studies at Copenhagen University and finally gaining her degree in physical science and mathematics at age 32.

There, at Copenhagen University, Inge became an assistant to a professor of actuarial science. Later, she got assigned to be an assistant to seismologist Niels Erik Nørlund. He showed Inge the ways we can study Earth's structure with earthquake data, which sparked her interest, so she began studying it on her own. At 40, Inge obtained a degree in seismology and was appointed the head of the Department of Seismology at the Royal Danish Geodetic Institute. She was responsible for running 3 seismic observatories, 2 of which were in Greenland and one in Copenhagen, where she also made time for scientific research.

Seismologists use transversal S-waves and longitudinal P-waves that travel through the Earth to determine what's on the inside. Originally, scientists thought of Earth's core as completely liquid, but this idea didn't quite fit with their measurements of the occurring P-waves. In 1936, Inge published a paper titled P´, where she wrote about the possibility of our Earth having a solid inner core. Her mathematical models described such a planet fitting perfectly with the P-wave measurements. Inge's theory was quickly getting accepted by other scientists, but it still took decades for it to be accepted universally.

Inge retired from the institute in 1953, but she definitely didn't stop working. She continued in her research, focusing on Earth's crust and mantle. She was traveling through North America, visiting various universities, and collaborating with fellow scientists. It led to her discovering another discontinuity of seismic waves underneath Earth's surface, this time much less deep than at the border of the inner and outer core – only 220 km under the surface, that to this day still hasn't been fully explained.

Inge never married or had children, passing away at the age of 104. She described her life as long, rich, and satisfying with many victories and good memories – victories that vastly expanded the knowledge of what's on the inside of our planet Earth.






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