Origins of volatile elements (H, C, N, noble gases) on Earth and Mars in light of recent results from the ROSETTA cometary mission

•The ROSETTA spacecraft is currently analyzing the composition of Comet 67P/GC.•From measurements by the ROSINA analyzer, we develop a model of comet composition.•Terrestrial water, carbon and nitrogen are probably not cometary.•Argon and other terrestrial noble gases could have been contributed by comets.•On Mars, comets could have contributed to the volatile inventory.