Re: Can hydrogen sulfide substitute for water as a basis for life?

Can hydrogen sulfide substitute for water as a basis for life?
Scientists always say that liquid water is necessary for life to
exist.  In cold environments (-60.7C to -85.5C), can hydrogen
sulfide perform the functions that water does for life on earth?
 
Well, maybe, but probably not around this corner of the galaxy.
 
That's an interesting question, however.   For us, hydrogen sulfide (H2S)
is almost as poisonous as hydrogen cyanide (800-1000 ppm can kill you in 30
min as opposed to 100-200 ppm HCN in 30 min).  It's just that the rotten
egg odor of H2S usually lets us know of its presence.
 
But life on earth has figured out how to live with H2S.  In deep-sea
vents bacteria live on the H2S coming out of the vent.  These
chemosynthetic bacteria oxidize the H2S as its energy source.  And some
have even proposed that H2S chemosynthetic life was the first life on
earth.  But water, "life's marvelous universal solvent" was still the
basis for that life, and for all the other life that followed.  To read
more about life in these energy rich but highly toxic environments see
Alissa Arp's site:  http://www.gene.com/ae/bioforum/bf01/arp/
 
What about other planets?  NASA has a good site about that:
http://www.resa.net/nasa/xlife_intro.htm
The NASA site talks about life in Jupiter's moons, especially Callisto and
Europa.  But they're still talking about subsurface water oceans, thus
they're still talking about water-based life.  Similarly, see
http://www.enterprisemission.com/europa.html

It just turns out that oxygen and carbon are so much better at forming the
sort of bonds useful for life that (I think)  wherever oxygen and
carbon exist, life will originate using them.  
 
What's so great about oxygen?  Well, it forms stable bonds with many 
other elements.  And in water, it is a polar compound with a dielectric
constant of 80, which means that the hydrogen has an extra little "hook"
which can form "hydrogen bonds".  This gives an extra range of new
attractions, and this versatility has put water at the top of the list of
elements useful for life.  By comparison, ammonia is 25.  Hydrogen
fluoride is 17.  And fluorine only has one bond per molecule, it could 
be a solvent, but its very limiting when trying to make the complicated
molecules needed for life.  And hydrogen sulfide is down with a dielectric
constant of 9.  Because of this, at one atmosphere, hydrogen sulfide isn't
liquid until -60 C. Pretty cold.  Maybe not impossibly cold for life, but
its molecules would be fleetingly unstable at our temperature.  And large 
scale energy for the synthesis of the early soup would have to come in 
somehow.
 
But at high pressures, H2S can be a liquid up to 100 C. So in a large
world with heating (stellar, vulcan, meteoritic, etc.), maybe life could
happen in a warm H2S ocean.  And maybe the same for ammonia, which can be
liquid up to 132 C.  The warmer it is the more I like it. 
 
But If there's any oxygen around, sulfur would rather combine with oxygen
than bond with carbon or hydrogen.  And nitrogen will be N2.  
 
Reasons like that also make silicon based life unlikely around here.
Silicon will form bonds with itself, but they're weaker than
carbon-carbon bonds.  And also if there's any oxygen around, the silicon
will form very stable Si-O bonds fast and you'll get sand (SiO2).  That's
why when Viking landed on Mars in 1976, NASA didn't include any 
experiments to look for silicon based life, although that was a popular
idea for Mars 50 years ago.
 
All this being said, were ready to get really speculative and answer the
question.
 
Well, what is life anyway?  Restricting ourselves to chemical systems, we
can say that life starts when a molecule becomes self replicating or at 
least becomes involved in its self-replication.   Other molecules may
become associated (ie. "enzymes", etc) that help in the replication, but
it's the replicating molecule itself which possesses the information for
its own replication. After that, everything including butterflies will
follow.  I'm pretty liberal about all this stuff.  I think given half a
chance, "life" or at least some sort of self-replicating system will
happen anywhere it can.
 
OK, if you had a planet with an H2S ocean that hadn't been blown away
after it's star ignited and had some energy source and gave it long enough
probably something like life could?/would? originate.  Where would that
be?

As Carl Sagan says, we're all stardust, because all our atoms (beyond
hydrogen) were made in the interiors of stars.  The atoms in our bodies
have been through about three stellar interiors!  The universe has about
an equal number of O (oxygen) atoms as S (sulfur atoms).
http://jan.ucc.nau.edu/doetqp/courses/env440/lectures/lec2/lec2.html
 
The sun has about three times the number of O than S atoms. 
http://csep10.phys.utk.edu/astr162/lect/sun/composition.html

(while the earth condensed with about 10 times the number of O than S
atoms)
http://zebu.uoregon.edu/disted/ph123/l10aa.html)

So I don't think the the "elements" are right around this solar system for
oceans of hydrogen sulfide.  Although apparently there are hydrogen
sulfide/ammonia crystals in the atmosphere of Jupiter.
http://galileo.ivv.nasa.gov/Jovian.html 
 
I'm not an astrophysicist, but I believe that as the universe ages,
heavier elements will build up, and in areas where there have been more
stellar generations, heavier elements will predominate.  And given all
the different ways things can happen, maybe a planet with an H2S ocean
could occur. And then yes, some kind of life based on liquid H2S
could happen.  But please remember this isn't my specialty and I'd enjoy
hearing from astrophysicists and exobiologists what they think of what I
have just written!  Mike Conrad.