transiently aquatic habitat, during the dry stages a larger number of dormant propagules are exposed to wind and thus dispersed. Freshwater organisms that must "cross the dry ocean" to enter new aquatic island systems will be passively dispersed more successfully than terrestrial taxa. Numerous taxa from both soil and freshwater systems have been captured from the air (e.g., bacteria, several algae, ciliates, flagellates, rotifers, crustaceans, mites, and tardigrades). While these have been qualitatively well studied, accurate estimates of their dispersal rates are lacking. Clouds The outdoor atmosphere harbors diverse microbial assemblages composed of bacteria, fungi and viruses whose functioning remains largely unexplored. While the occasional presence of human pathogens or opportunists can cause potential hazard, in general the vast majority of airborne microbes originate from natural environments like soil or plants, with large spatial and temporal variations of biomass and biodiversity. Once ripped off and aerosolized from surfaces by mechanical disturbances such as those generated by wind, raindrop impacts or water bubbling, microbial cells are transported upward by turbulent fluxes. They remain aloft for an average of ~3 days, a time long enough for being transported across oceans and continents until being finally deposited, eventually helped by water condensation and precipitation processes; microbial aerosols themselves can contribute to form clouds and trigger precipitation by serving as cloud condensation nuclei and ice nuclei. Living airborne microorganisms may end up concretizing aerial dispersion by colonizing their new habitat, provided that they survive their journey from emission to deposition. Bacterial survival is indeed naturally impaired during atmospheric transport, but a fraction remains viable. At high altitude, the peculiar environments offered by cloud droplets are thus regarded in some aspects as temporary microbial habitats, providing water and nutrients to airborne living cells. In addition, the detection of low levels of heterotrophy raises questions about microbial functioning in cloud water and its potential influence on the chemical reactivity of these complex and dynamic environments. The metabolic functioning of microbial cells in clouds is still albeit unknown, while fundamental for apprehending microbial life conditions during long distance aerial transport and their geochemical and ecological impacts. Aerosols affect cloud formation, thereby influencing sunlight irradiation and precipitation, but the extent to which and the manner in which they influence climate remains uncertain. Marine aerosols consist of a complex mixture of sea salt, non-sea-salt sulfate and organic molecules and can function as nuclei for cloud condensation, influencing the radiation