Geologist of the Month: Inge Lehmann!

Geologist of the Month: Inge Lehmann!

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What a cool lady! Inge Lehmann was a Danish seismologist who discovered that Earth has an inner (solid) core and a outer (molten) core.

Inge Lehmann

Born in Denmark in 1888, Inge was lucky to attend a progressive school where boys and girls were treated equally. Her studies continued through college where she received a Master's of Science from the University of Copenhagen in 1928 and subsequently was appointed State Geodesist of Denmark as well as head of the Seismological Department of the Royal Danish Geodetic Institute.

During her post, Inge became interested in the travel time of seismic waves generated by earthquakes.

Geo fact: An earthquake occurs when tension in rocks in the deep crust/upper mantle finally releases and those large areas of rock move along each other (faulting). That tension release results in shock waves that can move through the entire planet! These are called 'P-waves' (Primary or compressional, move through liquid and solid) and 'S-waves' (Secondary or shear, only move through solid or semi-solid).

P & S Waves

In 1929, a large, 7.3 magnitude earthquake rocked the South Island of New Zealand. While studying the seismograph data from this tectonic event, Inge noticed P-waves that should have been deflected by the earths core, were actually recorded at some seismic stations. She theorized that these waves traveled some distance into the core and bounced off of some kind of boundary.


Geo fact: In olden times, the earth was thought have a solid mantle with a liquid core.

Inge's calculations from this earthquake were the foundations for a 1936 paper, entitled "P", in which she theorized that Earth's core consisted of a solid inner portion with a liquid outer portion. It wasn't until 1970 that advances in seismology confirmed her theory was correct, and the boundary between the liquid outer core and solid inner core came to be known as the 'Lehmann Discontinuity'.

Ms. Lehmann was awarded the William Bowie medal from the American Geophysical Union (AGU) in 1971, where she was described as being "the master of a black art for which no amount of computerizing is likely to be a complete substitute."

Inge Lehmann lived to be 105 years old.

Want to know more?
To learn more about Inge's work and how we study tectonic movement, check out the following websites:

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