I just read a cool science news story from Natural History magazine by Robert R. Dunn: "A head in the clouds: do the microorganisms that circulate in the atmosphere get there by chance or by contrivance?"
I had honestly not thought much about clouds, much less clouds as active biotic realms. Apparently, there are microbes that secrete a variety of chemicals to escape the sea, play a role in creating clouds, and induce rain or snow to escape back to sea or earth. According to the article, the key research question now isn't whether microbes do such things, but whether the microbes have been naturally selected to do this (i.e.whether they do this "on purpose") or whether the chemical processes are byproducts of other microbial activities. In any case, I'll be looking at clouds a bit differently from now on.