"TomHendricks474"  wrote in message
news:civqjk$db4$1{at}darwin.ediacara.org...
> >> TH
> >> If life is a reaction to the sun/heat cycle, then
> >> you can't have life without the sun/heat cycle.
> >> And you can carry that further (same size
> >> planet to hold in a similar atmosphere - watery
> >> such that liquid water is there - temp zone
> >> between 0-100C, and on and on.
> >
> >Ah...  Well, the more similar attributes that you abitrarily add
> >between here and another life-giving planet, the more likely that
> >life will be the same form, and on and on.  But there's no real
> >reason that the same size is necessary nor that the atmosphere
> >is similar - after all, life began with a different atmosphere.
>
> TH
> Yes but it is that different reducing atmosphere that
> is a requirement for all life. And that specific
> environment can only be held by the gravity of a planet
> like earth. Bigger - (gas giant) and holds too much gas
> smaller (Moon or Mars) and it's gravity  is too weak to
> hold in the necessary atmosphere.

I was responding to your phrase "*same* size" (emphasis added), and fully
agree with the extreme of gas giants.  But let's take Mars - the jury's
still out as to whether there was ever life there - how many $ are now being
spent to find that out?  So what I'm saying is there's a reasonable range of
masses that might well support life and the closer the mass (and other
attributes) is to Earth's, the more likely that life will be similar.
Conversely, the more divergent the attributes (while remaining in whatever
range where life *can* begin), the more likely that life will be of a
"different form".

And I won't even concede that a very close comparison (very similar star,
planet, etc.) that produces life will do so such that DNA or a "variant" is
at the base of the evolutionary mechanism (except analogously, and once
again, panspermia aside.)

> Then too we go a step further - rocky planets are near
> the Sun (mercury - to Mars) while gas giants farther away.

True in our system, but IIRC, we've found gas giants much closer to their
suns in other systems.

> So to have a rocky planet - size of earth, it has to be in the
> same life zone.  Also if all this is a sun too hot - it'll burn up
> in a billion years before inteligent (?) life has time to form.

Intelligent life is irrelevant to the topic.  And since we went from solely
single-cells to intelligence in (arguabley) 800MY with "diversions" such as
~163MY of dinosaurs, I won't concede your point anyway (just because it took
3.xBY here doesn't mean it absolutely can't happen faster).  And there's all
sorts of star sizes that won't burn up for 2BY, 3BY, 4BY, etc., right up to
and beyond our sun's ~9BY.  You're frequently taking extremes for your
examples and not discussing all sorts of other intermeadiate possibilities.

> So it has to be a sun sized star.

No.  See above.  (Of course, I could be wrong, but I'm sure you'll let me
know if and where I am.)  :-)

> So for life to exist it has to have a similar sized sun,
> a similar sized rocky planet in the life zone orbit, etc. etc.
> And it is even likely that it took a planetoid collision that
> formed the Moon - to set up the orbit spin that sets up .
> the heat cycle that starts life.  Now that is very very very
> very specific conditions for life (and there are many more conditions)

I would disagree, based on my above comments.  Unfortunately I do not have
the training to quantify the range of star and planet sizes where I think
life could possibly evolve, but I clearly feel the range is significantly
greater than do you.  However, I have laid out my reasons.  Comments?

> (snipped)
> >> TH
> >> Because chemistry obeys laws. You can't change
> >> the chemical rules. They lead to the same result,
> >> at the same temp (liquid water range) and under
> >> the same conditions (liquid water - certain
> >> atmosphere etc.) with slight variation
> >True about basic chemicals.  But I'm suggesting that you can't know
> >that Earth's (raw materials and) chemistry is the only one capable of
> >producing life.  That is, a different elemental mix might produce a
> >different form of life.  And for that matter, a similar mix might
> >produce something pretty profoundly different from DNA-based
> >life (I'm not thinking that we can even guess at what that might
> >be - after all, did we successfully guess at a structure for DNA?).
> Th
> True - no one can pin down the future. But for a
> carbon based life form (and remember life here is
> based on the most common elements available  - so
> any other kinds of life (if there is such) must be built on
> uncommon and hard to find elements - thus this too
> suggests that it would be rare indeed if possible at all.
> Also see new  post on 'Why Early"

Yes, I've responded to that.

> (snipped)
> >Interestingly, the last few decades has taken the opposite direction.
> >Extremophiles are now found deep in the rocky mantle, high in the
> >atmosphere and around oceanic vents, where we used to assume
> >life was impossible.  If life has evolved elsewhere, I think we'll find
> >it can thrive in even more extremely diverse and "inhospitable"
> >(from our viewpoint) habitats than ones just here on this planet.
> >If I were a betting man and thought that any of this can be proven
> >in my lifetime, I'd even propose a wager that whatever life we
> >find will not have DNA, nor anything we'd consider a variant,
> >as its base.  Regards,  Brett.
>
> TH
> I think the extremophiles are here because
> they've had almost 4 billion years to adapt.

I've questioned this elsewhere - how sure are you about this date?  The fact
that some people think OOL and oceanic vents might be connected makes me
feel that *those* extremophiles have been around roughly since the
beginning.  Given their nature, it wouldn't surprise me if they've all been
around for quite some time.

> I think the common ancestor probably were
> all in a similar environment such that no
> extreme variants would have been stable
> enough to survive at the start.

Please clarify.  Do you mean at OOL?  But how about after several hundreds
of millions of years?  That'd still make 'em fairly old.

> I assure you, no one loves to speculate more
> than I on this. I've written a few sci-fi
> pieces (plug here - see my website for the
> short sci-fi novel "Library Planet" for ex.
> musea.digitalchainsaw.com) But the more I
> have learned , the more convinced I am that
> for the most part life is very specific to
> a certain place, condition, time, gravity,
> and all the rest.

Comments on my rebuttals would be appreciated.

> But again no one knows the future except
> Cassandra and who's listening to her?

Regards, Brett.
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