Résumé
The terrestrial atmosphere evolved through time as a result of exchanges of volatile elements with the mantle, the crust, and the outer space. Measurements of noble gases and nitrogen in Archean rocks (barite, hydrothermal quartz, cherts) give insights into the composition of the atmosphere at the time of rock formation. Trapped fluids consist of a mixture of one or several hydrothermal component(s) with an atmospheric end-member, presumably contributed as atmospheric gases dissolved in fresh- or sea-water. The isotopic compositions of Archean neon, argon and krypton appear similar to the present-day ones for radiogenic or fissiogenic isotopes. Compared to extraterrestrial precursors, Archean atmospheric xenon is enriched in its heavy isotopes by 1-2 %/amu, and intermediate between chondritic and modern atmospheric. We interpret this difference as resulting from a preferential escape of Xe backwards through time, due to its increasing photoionization by hard UV light from the young Sun deep into the atmosphere and a more efficient trapping interaction with the primitive organic haze. 3.5 Ga ago, the (super 40) Ar/ (super 36) Ar ratio was 143+ or -24, which, when integrated into a 3-box (mantle, crust, atmosphere) K-Ar model, is consistent with a significant volume of felsic crust between 30% and 55% of its present-day volume at that time. The partial pressure of atmospheric N (sub 2) was similar to, or lower than, the present-day one, and the Archean N isotopic composition was similar within 2-3 ppm to the modern one. These results indicate efficient magnetic shielding of the atmosphere since 3.5 Ga, and, together from estimates of the density of the Archean atmosphere, set constraint on the P (sub CO2) in the Archean atmosphere at <0.7 bar.