The more I read about the function of the Moon & tidal forces of the Earth-Moon system the more I realize the criticality of the moon's existence to the formation of life on Earth. So looking for rocky planets with a stars presumed "habitable zone" is only the first step, and one that doesn't get you very far toward finding life.
I didn’t say a stable star’s habitable zone is the only requirement for life. A large moon could also be necessary, or maybe not. There could be a thousand requirements, or just a few. Life could evolve under completely different conditions than our own, or maybe not. A single example is not enough to form a statistical basis for determining the probability of life in the universe apart from ourselves.
“. . . the more I realize the criticality of the moon’s existence to the formation of life on Earth.”
And if that’s the case (and I tend to agree, not that I’m any expert) that tends to argue for the scarcity of life as we know it elsewhere in the universe. That’s especially so because of the size of our moon relative to the size of Earth (a complete aberration compared to what we see in the rest of the solar system); and because of the circumstances of it’s formation. As I understand it, the best theory is that the moon was formed as a piece of the proto-Earth knocked off by a collision with a massive object of just the right size that had to hit with just the right velocity and just the right glancing angle to give us the system we have now.
If all that’s the case, the chances of that happening elsewhere aren’t all that high. I’ve always thought that the argument “since there are 10^n stars in the universe, that number is so large life *has* to exist somewhere else” is flawed by the realization that if the odds of getting things right for the initiation of living systems are 10^-n, we’re it. And if the moon and it’s formation in the fashion described above are crucial, achieving a potentially viable system may well be a real long shot.
The Moon causes 2/3 of the tides, the Sun causes 1/3, IOW, even without the Moon, we'd have tides. And take your copies of "Rare Earth" and throw them into the recycle bin.