The essence and origins of life. What is it? Yes, we can define characteristics that differentiated the living from the non-living. The building blocks of life are still not the same as a simple virus. Do you think new forms of life "become living" these days?. Do you think that the conditions to form new life simply do not exist anymore? Evolution can not even begin until something (still yet unknown to us) happens first. Do you think we will ever discover the recipe?
The whole question of how life arose has been a tough nut to crack, scientifically. And in part it's for the reasons you allude to here--the conditions have changed--life itself has changed many of them, ironically--and we don't really know what they were.
It gets worse if it turns out to be a very improbable event, because whatever the process is, it will depend on something really unlikely happening, so the actual correct explanation would probably be dismissed as ridiculous (remember those cartoons of the scientists talking over a diagram that has "and then a miracle occurs" in the middle of it?) even if someone were to hit on it.
The original conditions giving rise to life may be ridiculously rare, but not nearly as rare as an infinite number of monkeys evenually typing Shakespeare's Hamlet. Given that the latest estimate of the number of stars is 300 sextillion, and the number of planets 3 or 4 times that number at least, the conditions that brought about life here are almost certain to happen elsewhere, not just in a few places but in a great many.
I quess, because of the vast distances, and low probability of encounter, there are lots of 'dreamers' in the universe, waiting. And I expect a few hungry predators...;p)
Our planet came into existence around 4.6 billion years ago. We have existed in some shape or form for somewhere between 100,000 and 250,000 years, and have understood the concept of alien life potential for probably less than 100 years. It is not a matter of size of alien, intelligence of same, ability to get to us, or any other element. The timing of such a life form's also becoming aware of space, within those billions of years would have to match ours. So it would have to time its evolution to a mighty fine degree to be at roughly the place we are in our awareness today.
Would an evolved life form even recognise us as worth bothering with. Looking at us through the lense of about 250000 years seems hardly worth mentioning. If another life form had millions of years of writen cultural history, surely ours would be only interesting in passing. While we were just getting the hang of tool making, they were exploring intersteller space, and starting to evolve on other planets for adaptation.
Unless we are atypical, it's not likely most other races will go on for anything like 250,000 years as civilized beings. We've had civilizations for perhaps 10,000 years or less.
Actually, once one gets to the point of toolmaking, that is about the end of development, isn't it? After that, it's just making better and better tools, physical and intellectual. I think an advanced race would have to recognize us as on the same path as them, even if they are far ahead of us. I don't think we can assume their ethics to be similar to ours, though.
I can imagine an alien population of intersellar shaman, making stops at sacred water planets. Where their tools are advanced, but they attempt to repair planets to support/maintain life. They would be driven by a vision of the sacred/practical that might not be ours. Their tools being used for some perceived higher purpose. Such a group might see us as an infection, needing eradication, or education.
Given the vast distances, if we ever receive a radio signal from a highly evolved alien species, they have probably died off by the time their signal reaches us.
Warf? Is that you?
They send us WOW, we send them Chuck Berry.