- How much do we owe the moon & Theia for our existence?
- How unusual are we in the universe?
In time possibly much more unusual and rare than in all of space-time, and given that the sun is a second generation star unless conditions are much better than they were here on Earth it may take a lot longer for (intelligent) life to develop than here. We may be 'early'.
So 'right now' we are probably rare in the sense that we are a space faring species that hasn't (yet) destroyed itself and that may happen only rarely, so rarely that there is never much or even any overlap in time between two species at that stage of development (or say, even the last 500 years or so if you want a larger window). That's 500 years to overlap across an extremely large population of stars and planets so it may happen but it is still a small chance.
But if you let go of the time requirement then I don't think it is all that rare for it to have happened multiple times.
Let me give one example of how important the Moon is: without the moon the tides would be very weak (just solar tides) and that would mean that there is no part of the world where aquatic life can easily evolve into amphibious life (no tides: no tide pools, so no half-way-house between land and water). It may still have happened but much slower.
Some interesting reading on this:
https://www.smithsonianmag.com/smart-news/australian-lungfis...
Have we decided if the moon affects tectonics or they are a happy coincidence?
The moon did shield us from many impacts however. All those massive craters were rocks that would have hit earth.
The latter two points might turn out to be extremely rare events.
(Put on your tinfoil hats.)
Maybe the Earth-Moon system was engineered. The solar system came together from a nebular cloud 4.6 billion years ago. The great impactor hypothesis points to the mega-collision around 4.5 billion years ago. During the early days of the solar system, the system was very chaotic. By applying tiny-but-very-precisely-calculated forces in that system, you could cause an impact. Sure, it's many orders of magnitude above what humans have accomplished, but the gravity slingshots that got the Voyager missions out of the solar system are the same principle.
There could be many 1000s of civilizations in the galaxy. Maybe we aren't that interesting to visit, especially since we always have a few wars going on, and we have nukes. Maybe they are watching us for anti-matter production, fusion, stopping burning fossil fuels, and a century of peace.
To me it would be much more mind-blowing if our earth/moon system actually was a one in two hundred sextillion-ish event, than if the universe is teeming with life.
Are those events that crucial for life?
To me this question is in answer to the Fermi paradox, the great filter .. is it behind us? Its important to answer because if its not behind us, then; not wanting to be hyperbolic but, we are about to end.
Apparently most of the computer models of the early solar system doesn't result in rocky planets this close to the sun. And when it does there are constant meteor strikes. So we could be quite improbable. However considering the size and age of the universe, if the filter is behind us in the form of improbability, it should look to us as something that is impossible.
Of course we could be a few hours from some autocratic idiot starting the last nuclear war, a few months from a terminal AI singularity, or a few years from a runaway climate or food web collapse. But, I see nothing in the Fermi Paradox requiring the end to be so soon. Even dozens of millenia is still the blink of an eye in geological or galactic time scales. Perhaps the filter is populating the solar system but not escaping to other star systems before the sun expands into a red giant?
If a tree falls on a planet 15 billion light years from Earth, does it matter to us? I think what really matters is how unusual are we in our galaxy and its neighbors.
[1] https://en.m.wikipedia.org/wiki/Large_low-shear-velocity_pro...
