Milutin Milanković, a Serbian engineer and mathematician, publishes between 1920 and 1941 his theory that cyclical variations in Earth's orbit — eccentricity (100,000 years), axial obliquity (41,000 years), and precession (23,000 years) — determine Earth's glacial and interglacial periods. He calculates by hand, over years, interned in Budapest during World War I, insolation curves for different latitudes over the past 600,000 years. His theory was ignored for decades and only confirmed in 1976, when analysis of ocean sediments (Hays, Imbrie, and Shackleton, Science 1976) demonstrated that glaciation cycles coincide exactly with Milanković's periods. Today his cycles are the standard framework of paleoclimatology.