re: #48 Fozzie Bear

Honestly, we don’t know that life didn’t evolve more than once here. What happened 3.5 billion years ago is anybody’s guess. Perhaps there were competing biological paradigms, proto-bacteria using different basic designs. Who the hell knows.

I guess the part that makes it cool, is maybe you don’t need carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur. Maybe you just need atoms to play the “roles” these elements play. That would make a huge difference in where we look for life elsewhere.

It’s inevitable that life exists elsewhere. It’s ridiculously unlikely for it not to. this just means maybe its not so specific about conditions as we thought.

Proving a negative like that is not something that can be done without testing every possible case in the set, something we can’t do here.

As for your second point - As is in the same column of the periodic table as Phosphorus, indicating As will act similarly to P chemically. Same relationship of Silicon to Carbon, which is why Sci-Fi writers often spin tales of silicon based life forms.

On you last point - this is why the Kepler satellite is so exciting - we will soon have clear evidence of Earth-sized rocky planets in the habitable ( = liquid water) zone of many stars. We will have evidence that our galaxy alone probably has billion of planets existing in habitable zones.