cannabineer
Ursus marijanus
I dunno.We are likely to have the answers to many of these questions before the century is out, how complex multicellular life arose and when. We are also most likely to have a census of biospheres in a sizable portion of the galaxy, if they exist. Snowballs in habitual zones should not be overlooked either, as earth was one for much of its history. Oxygen is what we are looking for, that carbon oxygen combo with water, oxygen means animal life, the way we understand animal life and things with enough energy to move and think. Nature has often had multiple starts on a problem; the eye evolved independently a half dozen different times and it might be the same for photosynthesis.
I'm more interested in biospheres and their frequency than about receiving radio signals from little green men, but speculation on them could lead to some useful insights. Once we have the capability to reliably detect biospheres several dozen lightyears out, we will know a lot more about the prospects of little green men by 2100.
When I contemplate Fermi’s paradox (“where is everybody?”) I gravitate toward grim hypotheses. (“You really really don’t wanna know.”)