>> TH
>> I don't think so. The extremophiles on planet earth took
>> 4 billion years to evolve that ability.
>
>I wasn't aware of this, but naiively assumed they've inhabited these niches
>for much (most?) of the past 4BY.  How sure are you about this?

TH
To see what was around then - search for stromatolites
They are the best guess as to the bulk of life for at least
a billion years or so.

>> Our common
>> ancestor probably was formed in a very specific
>> set of circumstances that began with a heat cycle
>> and water in liquid form (which limits the heat cycle
>> to an amazingly short short short temp range - and
>> if its also a wet/dry cycle, then we are left with
>> an almost exact temp range of near 100C to allow
>> for water and steam both.
>
>I don't dispute any of your probability (my earlier post stated "I think
>you're likely right about the heat cycle"), but think that unless life is
>extraordinarily rare (and barring panspermia) that there will likely be
>more that a double-helixed, quad-spanned (my whuffo-like term)
>nucleic acid as the only possible basis of an evolutionary mechanism.

TH
Here's the hard part - back up that with some studies.

>
>> Further an important clue is that nucleic acids
>> absorb UV at 260nm. IF that is indeed a key
>> element then life is almost point-on specific.
>> Your scenario of anything goes would have to be
>> supported by some 'for instance' before I would
>> change my mind on this.
>
>To clarify, there wasn't an "anything goes" scenario.  I stated, rather
>"(there will not be an infinite variety of chemicals that can produce life,
>but there's probably >1 - a wild guess.)"  and  "I'm
suggesting that you
>can't know that Earth's (raw materials and) chemistry is the *only* one
>capable of producing life."  (emphasis added.)
>
>And I won't grasp at 'for instances', partly because, as stated, "I'm not
>thinking that we can even guess at what that might be"  and 
"we'll likely
>never know".  I'm also not trying to change your mind, but was only
>providing your requested comments.
>
>However, I will suggest that when people have argued for limitations such
>as
>life can only take the one form it has taken here on Earth, (or "we'll never
>fly"; "we'll never get to the moon"; "all that can
be invented has been
>invented", etc., etc., etc.) the limitations are frequently proven invalid.

TH
Who knows. This is something that we can only
wonder about when we go too far outside the
basics we have been talking about.


(snipped)
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