Re: So, why don't we still have dinosaurs?
Perhaps life did start multiple times in Earth's distant past but it cannot do so again while every habitable environment on the planet is infested with organisms selected by millions of years of evolution to be efficient at exploiting their environment.
This. All of this. And entirely this.
Even the humble garden slug is an ultimate bad-ass in its own niche. It has fought and defeated every challenger for its particular (narrow) environment. Having evolution start all over again - a fresh roll of the dice to spawn entirely fresh organisms - is not impossible, in my view. However, it'd be like putting a newborn infant up against special forces troops. In a straight fight it's just going to lose.
The only option is for this new evolution to find an unexploited niche. Perhaps this is why extremophiles are just so bizarre - maybe they have arisen as totally fresh instances of life, separate from whatever chains have spawned us, and they've just been the first into that environment. Maybe not.
Who can say? Without a way to go back and see it's impossible, and the car's in the workshop today - brakes are binding, so getting 88mph is a bit of a slog. Besides, the flux capacitor is being tricksy just now.
Biting the hand that feeds IT
