In 1824 Danish-Norwegian geo-scientist Jens Esmark published a paper claiming that there was indisputable and sufficient evidence to prove that the Norwegian landscape had previously been covered by enormous glaciers that had carved out valleys and fjords, glaciers reaching down to sea level. The erratic boulders of Northern Europe and the Alps and Jura mountains he likewise explained, and presented an astronomical theory of changes in the eccentricity of Earth’s orbit to explain the climate changes indicated by the field observations, a clear precursor of the Milankovitch theory. More and more Esmark has been recognized as the discoverer of ice ages, yet the genesis of his glacial paper has remained almost a complete mystery. Based on previously unpublished sources the present paper shows how the discovery represented the convergence of several paths in his research interests and activities previous to 1824. First, a deep interest in weather and climate; from January 1799 to December 1838 he made thermometer and barometer readings three times a day, and in practice became the first Norwegian state meteorologist. Secondly an interest in the determination of conspicuous ‘lines in the landscape’ such as tree-lines and snowlines, which he measured barometrically on first ascents of many of Norway’s highest peaks. Esmark also cooperated with a number of naturalists who studied extant Norwegian glaciers up close, providing them with his barometers for altitude measurements of glacier fronts and snowlines. Fourth, Esmark pondered the genesis of fjords and valleys in Norway, seeking an erosional agent that could explain the removal of large rock masses. Fifth, during a three month long voyage in the summer of 1823 along the Norwegian west coast and a subsequent mountain traverse, Esmark and two accompanying students made a series of crucial observations of moraines and polished cliffs that indicated former large scale glaciations down to the seashore. During the mountain crossing they studied glacier effects and moraine formation up close. The mountain path they followed and which extant glaciers they examined have until now been unknown and subject to much speculation. The present paper for the first time documents their mountain traverse – the path and the observations that early September 1823 led to the discovery of Scandinavian Ice Ages.