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  #5  
Old 02-02-2017, 06:09 AM
Leah S Leah S is offline
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Join Date: May 2008
Posts: 17
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Eric - thanks for the support.

Mark - just to point out that the Miller experiment was based on a mistaken view of the composition of Earth's early atmosphere. it's been repeated successfully with those same starting materials, but that's apparently not what the Earth's early atmosphere contained; and it doesn't work with other starting materials which reflect our current understanding of Earth's early atmosphere. as for "self-assembling molecules" - snowflakes and crystals can self-assemble but they aren't alive. regardless, a short polypeptide chain or even a longer random chain of amino acids is not a functional protein. and my point was that even "primitive" life is not really that "primitive" when we examine all the activities and *functional* complex molecules that it requires.

Pete - I didn't speculate on the possibility of some kind of life arising somewhere else in our galaxy or in another galaxy, if an Earth-like planet exists with the proper components and the proper distance from a suitable star. I was talking just about our own solar system where there is only one Earth-like planet. the part that bothers me is the automatic assumption that "primitive life" will automatically arise whenever there is liquid water, or some other solvent, such as alcohol or methane. the complexity required, and the statistical probability of that happening, are amazing enough on our own planet, which has had moderate temperatures and liquid water for billions of years. and yes I know that the first bacteria appeared within half a billion years after the Earth cooled down enough to have liquid water, as Mark mentioned. that just makes it more amazing, it doesn't mean that it happens automatically.

there is a joke about an immigrant who got off the steamship in New York and saw a silver dollar on the pier. he was about to pick it up and then he said to himself - why should I bend over just for silver? the streets in America are paved with gold!!!

regardless, if it were "easy" and "automatic" for life to arise, then it would have happened more than once on Earth. so I think it's unrealistic to extrapolate to other planets or moons in our solar system with less-than-ideal conditions. e.g. even if Mars might have had water at one time, it wasn't in the same quantity or for the same length of time as on Earth. and even if Europa might have some kind of "ocean" under a thick coat of ice, it gets much less sunlight due to the distance, and temperatures are extremely cold - which makes it difficult for chemical reactions of any kind to take place.

as for the possibility that some other molecule might fulfill the function of DNA - it doesn't matter what molecule fulfills the function of storing and transferring the information, as long as it is suitably complex for the task; the question is how a method can arise where one molecule (such as, but not limited to, DNA) can *code* for another one. i.e. not only do we need a functional polymer (protein or otherwise) with suitable variable units, but also a method with instructions to repeatedly assemble it. and a random chain of amino acids is not necessarily a functional protein.

it's nice to dream about finding extraterrestrial life, but I really doubt if any of the other planets or moons in the solar system has the conditions for it. in any event, the claim that any presence of water, even for a short time, will inevitably lead to "primitive life" is highly unlikely.
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