We study how different mechanisms contribute to changes in long term evolution. In particular, the primitive history (the first Gy) of terrestrial planets is heavily influenced by collisions. We investigate how the coupled evolution of Venus' atmosphere and mantle is modified by those impacts. We focus on volatile fluxes: atmospheric escape and mantle degassing. We observe that large impacts are unlikely to erode the atmosphere significantly. They are, on the contrary, an important source of volatiles for the primitive planet. Collisions also generate a lot of melting and rapidly dries the mantle through degassing. Without recycling of volatiles into the mantle (like in plate tectonics regime), the mantle is efficiently depleted.