{"id":4794,"canonical_url":"https://www.kudos365.com/today-in-history/events/1936ce-mar-29--4794","name":"1936 CE, March 29","year":1936,"era":"CE","month":3,"day":29,"url":"https://www.kudos365.com/today-in-history/events/1936ce-mar-29--4794","iso-date":"1936-03-29","precision":"year-month-day","description":"\u003cp\u003eDanish seismologist, Inge Lehmann sends a letter on March 29, 1936, to Harold Jeffreys, a leading authority in geophysics, describing her hypothesis that that Earth’s center consisted of two parts: a solid inner core surrounded by a liquid outer core, separated by what has come to be called the Lehmann Discontinuity. \u003cbr\u003e\u003c/p\u003e","additional_details":"\u003cp\u003eAt the time, geophysicists believed Earth to be made up of a liquid core surrounded by a solid mantle, itself surrounded by a crust, all separated by abrupt density changes in the Earth called “discontinuities.” She had arrived at het hypothesis by analyzing multiple records of earthquake shock wave data results which consisted of P and S waves, one of them the large, June,1929, New Zealand earthquake. She went on to publish a paper in September 1936. succinctly called “P′,” arguing for what now is taken for granted: That buried inside the Earth’s molten layer is a solid core. Lehmann’s hypothesis was confirmed in 1970 when more advanced seismographs detected waves deflecting off this solid core. \u003ca href=\"https://www.aps.org/apsnews/2023/08/seismologist-lehmann-earth-inner-core\"\u003eMore\u003c/a\u003e\u003c/p\u003e","photo":"https://k365fs.imgix.net/bJXaNaTSqUvosGZFr7xA_Inge_Lehman%20-%20PDR.jpg?auto=format,compress\u0026fit=clip\u0026max-w=1600","photo_width":1600,"photo_height":1176,"created_at":"2026-03-29T12:44:37-07:00","updated_at":"2026-03-29T12:48:30-07:00","breadcrumbs":{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"March History","item":"https://www.kudos365.com/today-in-history/march"},{"@type":"ListItem","position":2,"name":"March 29","item":"https://www.kudos365.com/today-in-history/march-29"}]},"schema":{"@context":"https://schema.org","@type":"Thing","@id":"https://www.kudos365.com/today-in-history/events/1936ce-mar-29--4794#eventK365","name":"1936 CE, March 29","headline":"Danish seismologist, Inge Lehmann sends a letter on March 29, 1936, to Harold Jeffreys, a leading authority... - 1936 CE","description":"Danish seismologist, Inge Lehmann sends a letter on March 29, 1936, to Harold Jeffreys, a leading authority in geophysics, describing her hypothesis that...","url":"https://www.kudos365.com/today-in-history/events/1936ce-mar-29--4794","additionalType":"HistoricalEvent","inLanguage":"en","datePublished":"2026-03-29T12:44:37-07:00","dateModified":"2026-03-29T12:48:30-07:00","publisher":{"@id":"https://www.kudos365.com/#organizationK365"},"image":{"@type":"ImageObject","url":"https://k365fs.imgix.net/bJXaNaTSqUvosGZFr7xA_Inge_Lehman%20-%20PDR.jpg?auto=format,compress\u0026fit=clip\u0026max-w=1600","width":1600,"height":1176},"temporalCoverage":"1936-03-29","isPartOf":[{"@id":"https://www.kudos365.com/#websiteK365"},{"@type":"CollectionPage","@id":"https://www.kudos365.com/today-in-history/march","name":"What Happened in March History"},{"@type":"CollectionPage","@id":"https://www.kudos365.com/today-in-history/march-29#pageK365","name":"What Happened on March 29"}]}}