Today in History is a daily newsletter from Britannica. (more) Today in History—March 29: A Woman Discovers Earth’s Core Written by Michele Metych Michele Metych is the lead editor for Today in History at Encyclopædia Britannica. Michele Metych Fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Mar. 25, 2026 •History The Danish seismologist who discovered Earth’s inner core built her theory using cardboard oatmeal boxes filled with index cards—each recording a seismic event—and she did the math by hand in her sunny garden. Today in History is a daily newsletter from Britannica.Encyclopædia Britannica, Inc. Want to learn more about what happened on March 29, or any other day of the year? Sign up to receive the newsletter in your inbox every morning. In doing so, Inge Lehmann...

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