If true, then I'd be worried about some Great Filter ahead of us (ie technology destroying us) as that may be a plausible reason why we haven't spotted aliens yet?
That the great filter is behind us. I expect primitive life to be common, and civilizations to be rare.
Or rather, the "great filter" is a series of probabilistic challenges which each instance of life either fails (regresses / stagnates) or overcomes, along with probabilistic events that jump things forward to the next "stage". If not for an asteroid long ago, dinosaurs would still rule the earth, perhaps.
1. Water bearing & warm planet.
2. Plenty of time for eukaryotic cells to develop.
3. Intelligent life doesn't destroy itself (by whatever means), and is not destroyed by highly unlikely events.
4. Heat death of the universe.
Think of them more as achievement levels in a video game. You might die on this level, but if you don’t and get to the next level, you have to avoid dying on that level, now.
First: if expansionist societies reliably destroy one another sometime after contact, remaining societies are not expansionist, and so (therefore) do not make contact. Expansionist societies that make contact and do not destroy one another continue expanding until they encounter another, and the dice are rolled again.
Second: if societies sufficiently advanced to make contact first master controlled-fusion tech, then goldilocks planets become uninteresting. Look for aliens near Kuiper Belt objects where useful molecules are in piles conveniently frozen to the bottoms of shallow gravity wells. In this scenario, planets like ours are used only by extreme primitives. The aliens already know we have nothing interesting to say to them.
I think that the step from Prokaryote to Eukaryote is much more difficult. (Feel free to disagree. Nobody is sure.)
[Assuming there was an ocean in Mars, and assuming there was life.] The problem is that the ocean disappeared, probably due to geological reasons that neither a unicelular or multicelular lifeform can solve. Sometimes you are just born in the wrong planet. https://en.wikipedia.org/wiki/Mars_ocean_hypothesis
Moreover, it's probably easier for an unicelular bacteria-like or archaea-like lifeform to survive. Some of the one from Earth can extract energy from some rocks or volcanic fumes, so they can survive in weird places.
Edit: Fixed "Eukaryote to Prokaryote" -> "Prokaryote to Eukaryote"
I think you mean from Prokaryote to Eukaryote?
Do you (or others) recommend any books exploring these conditions of life? The biology course I took online dabbled in explaining the difficulty of biological existence but wasn't the purpose.
if true, the number of such species might converge to one over time.