|Inge Lehmann (Source)|
1. Her Study at a Mixed School Led to Disappointment
Lehmann attended Denmark's first co-educational school, founded by the aunt of Neils Bohr, Hanna Adler. She learned there that boys and girls could be treated alike for work and play. She later said in 1980, "No difference between the intellect of boys and girls was recognized, a fact that brought some disappointments later in life when I had to recognize that this was not the general attitude." While today mixed or co-ed schools are more common, women still struggle to be recognized as equal to men in intelligence.
2. Her Parents Didn't Want Her to Study Math
Inge’s interest in mathematics was encouraged by a teacher there, but her parents objected to it because they thought she wasn't strong enough. However, she passed the entrance exam with first class standing. "They could not be expected to understand, I suppose, that I should have been stronger if I had not been so bored with school work." Lehmann later said.
There's a general bias against women studying math even today. In fact, it wasn't until 2014 that Maryam Mirzakhani became the first woman to win the "Fields Medal" which is the most prestigious award in mathematics.
After a few years of work in the insurance field, she became an assistant to the geodesist Niels Erik Nørlund. He assigned her the work of setting up seismological observatories in Denmark and Greenland. This was the beginning of her interest in seismology. In 1928, she passed her exam in geodesy and accepted a position as state geodesist and head of the department of seismology at the Geodetical Institute of Denmark led by Nørlund.
3. Her Study of Earthquakes Led to the Discovery of the Earth's Core
Since the 1890s studies of gravity concluded that the Earth had a core at it's center. But, studying the Earth's core is extremely difficult because it's impossible to drill more than a few miles in the Earth's surface. The mantle, under the Earth's crust, is 1800 miles below the surface. So since the early 1900s studying earthquakes has been the main way that scientists have studied the core. Richard Dixon in 1906 discovered that there was a core in the center of the Earth, but Lehmann noticed something else.
In 1929, she was studying shock waves from a large earthquake near New Zealand when she noticed a difference in the seismic data. Lehmann asserted that because some P-waves, pressure waves that are the first waves from an earthquake to arrive at a seismograph, which should have been deflected by the core, were not deflected then a layering in the core must be present. Lehmann theorized that this layering of a solid inner core and the liquid outer core must is separated by some sort of boundary between them. This boundary is known as the "Lehmann Discontinuity" and for over twenty years was highly controversial until it was also finally confirmed in 1970.
"Lehmann’s Discontinuity" theory broke from conventional wisdom that claimed the Earth’s core was liquid followed by a solid mantle and then surrounded with a crust. Each change in composition was considered to be abrupt and was called “discontinuity”. What became named the Lehmann Discontinuity theory also led to new thinking about the Earth's overall composition as well.
4. Nuclear War Led to Better Earthquake Research
The Depression and the Second World War cut back dramtically on seismographic research. What equipment remained was a hodgepoge mix of seismographs recording on smoked or photographic paper. They were largely uncalibrated and responded to waves in different frequency ranges and recording at various rates. But, as nuclear testing increased, there was a need for more sensitive equipment to monitor underground nuclear testing.
President Eisenhower set up a panel charged with improving seismic surveillance of underground nuclear explosions. This led to a boost in funding around the world to develop improved and standardized seismographs. These new seismographs were installed in the early 1960s at over 200 existing seismographic stations around the world including Copenhagen.
Lehmann's amazing ability for reading and coordinating seismic information was instrumental in helping the United States in it's nuclear ambitions. In return for their work, they funded further exploration of the structure of the upper mantle. Lehmann had no interest in nuclear politics, but those policies led to an increased understanding of our world.
Lehmann lived to 104 years old and told a relative "You should know how many incompetent men I had to compete with--in vain." A woman living in Denmark not only overcame the stigma of women in math and science, but used nuclear weapons testing to understand the world we live on.
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