Text 176, 177 rader
Skriven 2004-09-27 05:58:00 av Brett Aubrey (1:278/230)
Ärende: Re: Different Forms of Li
=================================


"TomHendricks474" <tomhendricks474@cs.com> wrote in message
news:cj4nbj$1t5a$1@darwin.ediacara.org...
> >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?
> TH
> You might want to read about the hypothesis of
> GAIA by James Lovelock. He told NASA that he didn't
> think life could be on Mars because the atmosphere
> was not a life atmosphere. Life on a planet changes
> the atmosphere.  So much so, that if you know the
> contents of the atmosphere, you know if there is
> life.  And there was nothing to suggest life on either
> Mars or Venus.
> NASA didn't like the notion - it would quickly end
> funding if it was widely held.

At http://www.ozi.com/ourplanet/lovelock2.html Lovelock queries "What is
Gaia?" but his response doesn't even mention "atmosphere".  Be that as it
may, my point stands... the jury's still out.  And Lovelock (by your post)
said his reason was because Mars didn't have a life atmosphere, and not
because the mass was too low to support life.  Will you give me at least a
possibility that a Mars-sized planet *could* support life under ideal
conditions?  Say, in an ideal orbit, an appropriate amount of water, a
"good" (Earth-like?) axial inclination and rotation period, etc., etc.?  Or
do you rule it out absolutely?

> > 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".
> TH
> I agree with the first statement.

Well, good.  Now I'll try to quantify a bit.  Let's say Earth is fairly
ideal (for argument's sake, I'll agree with you here) and Mars is on the low
end for mass.  Might you agree that, therefore, the range is roughly an
order of magnitude either way from earth's mass?  That would give a pretty
wide range, IMO, and *well* outside what anyone would consider "same sized".

> I would say, 'the more divergent the attributes',
> the less likely that life will be at all.

Well, of course this is what you would say.  Would you care to try
quantifying it?  Are you, for example, saying that life's impossible on any
rocky planet outside +/-5% of earth's mass?  +/-10%?  +/-20%?  What is your
boundaries for "same sized" planet?

> (snipped)
> >> 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.
> TH
> But a hotter sun means the planet has to be farther out to
> be in the life zone. Farther out means a less circular orbit
> and a greater variation in temps - perhaps the hot summer
> would be too hot and cold winter too cold to keep water
> liquid form (switch from Mars like to Venus like and back)
> What I'm saying is not the extremes but pretty close to the norm.

You're going into areas of unfamiliarity for me, but I thought Neptune's
orbit, for example, was closer to circular than Earth's and Mercury's was
less so.  And I see from:
http://cannon.sfsu.edu/~gmarcy/planetsearch/bd/ecc.html ...

 "The circular orbit of Jupiter in our Solar System promotes
  the stability of circular orbits among the other 8 planets.
  If our Jupiter were in an eccentric orbit, the Earth and
  Mars would likely be gravitationally scattered out of the
  Solar System. Thus our existence, and the existence of
  life in the habitable zone, depends on both Jupiter and
  Earth being in mutually stable, circular orbits."

If I understand these more or less correctly, then there's nothing stating
that further out *absolutely* means more varied.  And even if I'm wrong
here, how much would it vary?  (You say "perhaps the hot summer...";  well,
"perhaps *not*", I'll shoot back.)

We can surely have some "variation in temps" over an annual period
(especially in polar regions) while, for example, maintaing an equatorial
(or other) region at an appropriate temperature for life to begin.  And I
don't think you can justify saying you're "pretty close to the norm" at all,
since we really don't know a norm for other planets.

But you still didn't realistically (IMHO) respond to my comment of all sorts
of sun sizes from, say "4BY, etc., right up to and beyond our sun's ~9BY".
This implies, of course, cooler suns than ours as well as all sorts of stars
a bit to significantly hotter.  Again, I take your comments as dealing with
the extreme of a (much, much) hotter sun (based on your "one billion year"
scenario), even if you're right about the eccentricity of orbits.  Your
other extreme, AFAIC,  was gas giants- what about rocky planets 2x Earth's
size?  3x? 5x? etc.  Maybe you have data I don't have, but the gas giants in
our system are 14x to 317x Earth's mass - in the absense of information to
the contrary, I'll assume that rocky planets of several times Earth's mass
are at least possible.

> >> 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
> >> 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 round for quite some time.
> TH
> The oceanic vents presents a lot of problems
> for me.
> The basic one is this - if life is a reaction to
> the sun it won't begin where no sun shines.

Of course, not all oceanic vents are deep...

> Archae may be very old and may be closer
> to the earliest common ancestor - but my point
> was that the farther you go back the more alike
> life would be. Today we have life that can live
> in a temp range below 0C to above 100C. I
> don't think you had any range like that when
> life began.

Well, I'll agree, of course.  What I question is your statement that "The
extremophiles on planet earth took 4 billion years to evolve that ability."

> And before that - anything that would
> be outside the range of the environment
> would not be stable enough to lead to life.

This seems self-evident - by definition, just prior to OOL (and related to
OOL) anything *must* be within the range of the environment(?) Am I
misreading you?

> >Please clarify.  Do you mean at OOL?  But how about after several
> >hundreds of millions of years?  That'd still make 'em fairly old.
> TH
> The evidence for a big chunk of the
> earliest history of life
> is that it wasn't much but stromatolites.
> Maybe the first 1-2 billion years. I don't
> think there was great variety that early on.

OK.  Point taken.

> >Regards, Brett.
Regards, Brett.
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