"This proposal has the objective to greatly enhance our understanding of sources, sinks and processes fixing the composition of the atmosphere at different time periods of time, from 3.8 Gyr ago to Present. For achieving this goal, I shall develop the high precision analysis of noble gases, which are key tracers of atmospheric evolution.The core of the proposal is : (i) the development of multi-collector mass spectrometry analysis of noble gas isotopes coupled with standard bracketing, aimed at reaching the per mil or better precision level, which will constitute a world premiere, (ii) the analysis of unique cometary samples, of ancient sediments already partly available at my laboratory, and of present-day air sampled at different geographical and altitudinal scales, (iii) the quantification of sources and sinks of atmospheric volatiles through the study of the fluxes of noble gas isotopes.With this proposal, I develop a new and extremely competitive area of geochemistry, aimed at better understanding the early evolution of our planet habitability, as well as at improving our knowledge of fluxes of volatile elements triggering anthropogenic climate change. This proposal will establish the leadership of Europe in high precision geochemistry of exceptional tracers, the noble gases."