The role of impacts in the evolution of the Earth’s atmosphere is discussed. Impacts could have been significant heating sources during the Hadean eon, and likely promoted thermal escape of atmospheric species to differing degrees. Large impacts, that are regularly delivering enough energy to Earth’s atmosphere to cause significant erosion, can also bring metal particles with catalytic properties in the right conditions. That impact-induced chemistry is poorly known, but recent laboratory studies emphasize its key role in the production of greenhouse gases and organic compounds. A better understanding of the phases associated with re-entry and cooling phases of a bolide plume evolving in the aftermatch of a huge impact is needed. In the right range of temperature and pressure conditions, impacts can produce ammonia, methane and other organic compounds through the Haber and Fischer-Tropsch catalytic processes, but mixing and decay of those compounds in different models of the atmosphere needs to be explored. Hadean-atmosphere models proposed so far are reviewed also discussing the scarcely available geological evidence. Simple thermodynamic equilibrium calculations for probable Hadean atmosphere conditions are presented. Several scenarios of reducing (H2-rich) and oxidizing (CO2-rich) atmospheres are considered to study the stability of CH4 and NH3 and the formation of organic compounds. Searching for chemical signatures in similar evolutionary stages of recently formed Earth-like exoplanets could be an interesting future field of research. New evidence in this regard can contribute to a better understanding of the transition point to a habitable world.