Earth-Sized Worlds

[Weltall]

2.) Life does not need to match set conditions. Our own planet has the x-treme sports family of species, the insects that can only live in the deadly gases and compost of a bat caves bathroom, the animals that gleefully accept the pounds of pressure per square inch that would make a human being the size of a can of tomato soup within seconds at the bottom of an ocean that has more depth than we have atmosphere. Things like that tell me the condition of the planet means very little when it comes to the possibility of life.

Life, as we know it, does need a certain series of variables to be within a certain range to begin. The fact that there are creatures now that have adapted to all sorts of environments only means that we have life and it is adaptable. It does not mean that life can begin in these same environments. Certainly, conditions other than what we have experienced on Earth would make the evolution of complex life much less likely. Any evolutionary biologist will tell you that earth won a rather tremendous series of lotteries when it came to the circumstances best suited to not just form life from lifeless material, but to allow that life to evolve to the point where it becomes self-aware and can dictate its own destiny.

That's why the seeding theory is not a very good one. Unless the seeds were spread all throughout the universe, the chance that this primal life material could take root anywhere and flourish is stupendously low. Lower still is the chance that the same seed material responsible for our existence landed on another suitable planet and developed into intelligence at the same rate or faster than we did.

See: Fermi's Paradox and the Rare Earth Hypothesis.