This conference presentation describes the invention of molecular carbon-13 dating, a relative dating method that allows to mesure the relative age of organic substances in complex. This invention is based on the discovery of temporal pools of molecular susbtances in soils. The findings open a new scientific field, named Molecular Chronology, to study the source, transformation, persistence, sequestration, transfer and toxicity of organic substances in complex media, such as living organisms, food, soil, waters and sediments. Similarly to sedimentary stratigraphy that uses layers to date sediments, molecular chronology uses temporal pools to date molecules. As a consequence, any biological or environmental samples becomes a 'fossil record' of substances of different age. Molecular chronology is thus expected to deliver new knowledge in all fields studying complex systems, such as biology, medicine, food science, agronomy, environmental science, soil science and geology. This is an invited conference at SIL2018, the Congress of the International Society of Limnology, in Nanjing, August 2018.