Jankelis Giršas Kersnenskis was born on 10 November 1914 in the town of Simnas, into a family of small farmers. His early childhood and the life of the whole family were disrupted by the First World War, during which the Kersnenskis family spent five years in the depths of the Russian Empire. In 1919, the family returned to Simnas. Every day from 1925 to 1934, Jankelis travelled about 30 kilometres from Simnas to Marijampolė to a private Jewish gymnasium. As a pupil, Jankelis showed a leaning towards the exact sciences – the highest grades on his high school graduation certificate were in chemistry and physics. After the gymnasium, in 1934, he joined the Lithuanian army and served for a year and a half in the 9th Regiment of Vytautas the Grand Duke of Lithuania. Shortly after military service, in 1938, Kersnenskis began studying chemistry as an auditor in the Faculty of Mathematics and Natural Sciences of the Vytautas Magnus University in Kaunas. At the end of 1939, when Vilnius was returned to Lithuania, Jankelis and some other students of the Vytautas Magnus University were transferred to Vilnius University. In Vilnius, he settled on Sodų Street, gave private lessons to schoolchildren, and was involved in university life as an auditor. On 19 September 1941, Jankelis Giršas Kersnenskis was expelled from the Chemistry Department of the Faculty of Mathematics and Natural Sciences of Vilnius University on the basis of the Order of 17 September 1941 of the Higher Education Department of the Board of Education, which was subordinate to the Nazis. Jankelis Giršas Kersnenskis’ further fate is unknown.