A fly flew over a stream of water.
A fish saw the fly and jumped out of the water to catch it.
A bear in the bushes saw the fish and jumped in the water to eat the fish.
A hunter saw the bear jump out and raised his rifle to shoot the bear. In so doing he dropped his sandwich to the ground.
A mouse saw the sandwich drop and jumped out to grab a piece of the cheese.
A cat saw the mouse and jumped out to catch the mouse.
The cat fell in the water and got wet.
The story highlights a chain reaction of events. Life is full of chain reactions. One thing causes another. Life is like dominos falling into each other and knocking the next one down. The question becomes whether it is inevitable that the first action leads to the final outcome. Given that the fly goes over the water, will the cat get wet? It is something to ponder.
If the planet is the right size, at the right place from it’s star, is it inevitable that life will evolve? The evidence suggests no. There were too many “lucky breaks” in the form of mega disasters for the earth that brought us to where we are now on a life sustaining planet. A mars size planet collided with Earth. It was a terrible collision. It spewed all kinds of rocks into space that coalesced into the moon. Without the moon, the earth would have wobbled and not have been stable to support life. The creation of Earth did not necessitate that there was a colossal disaster that resulted in the moon. Call it bad luck. Really good luck.
The Earth is lucky. Luck is luck. It’s a chance. In our case maybe one in a million. Maybe, perhaps, the only time. Maybe there’s somebody else out there, maybe there isn’t. So far, we haven’t seen evidence of anything out there other than what came from here.