This is just speculation, so my numbers are only approximations...
Considering the likelihood of the existence of life, let's reflect on the conditions necessary for life to exist.
First, it's very likely that any sun has planets, say a 100-to-1 shot.
Second, it's less likely that a planet settles into an orbit around it's sun in the "Goldilocks" distance from its' sun, say a 1,000,000 shot(orbital distances are huge). Too close, chemical reactions leading to life are unlikely(too hot). Too far, and those chemical reactions happen too slowly(too cold).
Third, for our type of life to occur, a planet has to have a plentiful supply of water. Water molecules are common. They aggregated to our planet from common icey comets, say another 100-1 shot.
Fourth(a), it took the first bacteria Billions of years to develop. 1,000,000,000-1 shot.
Fourth(b), for our type of life to evolve from the first bacteria, it took Earth about a Billion years, another 1,000,000,000-1 shot.
Fifth, for that life to survive, it had to endure/survive various extinction events, like asteroids, cosmic-ray blasts, pandemics, climate changes, etc., over that Billion years. Another 1,000,000-1 shot.
Sixth, in our case, we would not have had a chance to evolve from our mammal rodent-like ancestors, if the Dinosaurs had not gone Bye Bye. Another 1,000,000-1 shot. Thank Goodness asteroid!
Seventh, once the dinosaurs were gone, we had to survive several Ice Ages during our Evolution from our primate ancestors. Another 1,000,000-1 shot.
Eight, we had to discover how to control fire, to build any kind of technology. 100-1 shot?
If you add all those together, we're LUCKY to be here!!!
