Inge Lehmann

Women in STEM
Inge Lehmann

Birth:  May 13, 1888

Death:  February 21, 1993

Specialty: Seismology, Geophysics

Major Contributions:

Discovered the Earth has a solid inner core inside a molten outer core

Discovered Lehmann discontinuities

The asteroid 5632 Ingelehmann was named in her honor

Image: Wikimedia.

In the early 1930’s scientists, using seismographic data, concluded that under the outer crust of the Earth there was a large metallic liquid core. But there was one problem with this conclusion, the data didn’t exactly match up with the theory.

Studying the time it took for the two types of waves created by earthquakes, S-waves and P-waves, to travel made it possible to track the types of materials the waves traveled through. And while the data did support a mostly molten core there were some pesky P-waves that didn’t follow predicted behavior; they would show up in locations they shouldn’t.

Geophysicist and seismologist Inge Lehmann, head of the department of seismology at the Geodetical Institute of Denmark, proposed that instead of the center of the Earth being completely molten there might be a solid inner core that could refract and reflect the P-waves. She developed mathematical models and tested them against the data, and it was a match. Lehmann calculated the inner core had a radius of about 1400 km and in 1936 published her findings in a paper simply entitled P’. 

As other scientists were able to use the earthquake data to reach the same conclusions, her theory began to be widely accepted.  Over time with more accurate seismic equipment making better measurements Lehmann’s solid core was accepted fully when in 1971 computer calculations supported her conclusions. 

Retiring from the Geodetic Institute in 1953 she traveled extensively in the United States where she continued her work on the Earth’s crust and upper mantle discovering another seismic discontinuity lying at depths between 190 and 250 kilometers.

Now known at the Lehmann discontinuity it is observed as an abrupt increase of P-wave and S-wave velocities at these depths that appear beneath continents but not usually beneath oceans and are still not fully understood.

Receiving many awards during her lifetime she has continued to be recognized for her work including the naming of asteroid 5632 Ingelehmann and in 2015 a new species of Dermestidae, or skin and carpet beetle, Globicornis (Hadrotoma) ingelehmannae, was named in her honor.

Written by Angela Goad


Wikipedia: Inge Lehmann

Famous Scientists: Inge Lehmann

Wikipedia: Lehmann discontinuity

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