Alien bacteria-like in their original planet: Nobody know, but yes. Some steps are easy, some steps are unknow. It's a little optimist to say a clear "yes", but "yes".
Intelligent Alien living happily in their original planet or nearby: Nobody know, but probably yes. There are more unknows unknows step here. I'm particularly worried abbot the prokaryote-eukaryote transition, but there are more steps and more unknow steps. So let's hope that the universe is big enough and say "probably yes".
Intelligent Alien visiting us in flying saucer: Nobody know, but probably no. The distances are too big. There is no hard evidence like a crash from time to time. We don't receive any electromagnetic weird signals, and electromagnetic communication is so efficient it would be weird that they use other means to communicate between starships. Absence of evidence is not evidence of absence, but let's say "probably no".
Intelligent Alien living happily in their original planet or nearby: Nobody know, but probably yes. There are more unknows unknows step here. I'm particularly worried abbot the prokaryote-eukaryote transition, but there are more steps and more unknow steps. So let's hope that the universe is big enough and say "probably yes".
Intelligent Alien visiting us in flying saucer: Nobody know, but probably no. The distances are too big. There is no hard evidence like a crash from time to time. We don't receive any electromagnetic weird signals, and electromagnetic communication is so efficient it would be weird that they use other means to communicate between starships. Absence of evidence is not evidence of absence, but let's say "probably no".