RE: Global Carbon Cycle [was RE: Number of carbon atoms in the Earth's biomass]

From: Spike (spike66@comcast.net)
Date: Thu Jul 24 2003 - 22:49:50 MDT

  • Next message: Brett Paatsch: "Re: Precisions on the Martinot situation"

    From: Robert J. Bradbury

    Subject: RE: Global Carbon Cycle

    On Thu, 24 Jul 2003, Spike wrote:

    > But it does leave some questions, such as why was
    > it so late in the game before a archaeo-carbon
    > scavenger evolved?

    Hmmm, spike you need to expand on this somewhat.
    All bacteria are carbon scavengers...

    Yes of course bacteria scavenge carbon from the
    soil, and for that matter all animal life scavenges
    carbon by devouring plant matter. But what I meant
    by archaeo-carbon is that carbon which falls into
    the cycle of peat to bituminous coal to anthracite
    coal to diamond.

    I would not be surprised if some lifeforms figured
    out how to break down peat, but I know of none which
    can break down bituminous, or the much harder anthracite.

    ... -- but the restrictions
    would seem to be on the lack of sunlight for
    photosynthesis...

    No. There are thingies living at the bottom
    of the sea which make their living breaking
    down the chemical soup that spews from deep ocean
    vents.

    ...or the lack of oxygen to oxidize
    the reduced hydrocarbons (for energy sources) --...

    Nyet. There was plenty of life on this planet
    before there was free molecular oxygen.

    ...iffy premises to base the conclusion of "decline" on...

    OK, do let us continue with your objections,
    out of order.

    > Carbon based life on this planet was already
    > very much in decline before the last few thousand
    > years when human started digging coal, [snip]

    ...I would question the use of the term "decline".
    Isn't life always adapting to the resource base
    that is available? There is no strict requirement
    that we are currently aware of that carbon must be
    the basis for "life". While it seems preferable
    proving it would seem to be very difficult...

    Ah, thank you very much for bringing this up
    Robert. At this point I shall boldly claim that
    carbon is the only material that is crucial to
    all lifeforms, not just those on this planet.
    Its chemical properties are unique in so many
    ways, there simply is nothing like carbon, nothing
    at all, not even close, not silicon or anything.
    When I look at my CRC handbook of chemistry and
    physics, and study all the compounds therein,
    over half of them contain carbon, and all the
    really interesting stuff is organic, with carbon
    making all those wonderful rings and chains of
    all different sizes and shapes. Carbon really
    is my very favorite atom.

    So are there any other candidates to be the basis
    of a life form for a carbon starved planet, such
    as the moon? First off, forget those elements
    which have only unstable isotopes, since chains
    could not last long if an atom were to transmute.
    Scratch 24 elements, 81 left with at least one
    nonradioactive isotope.

    Five of those are out, the noble gases, not nearly
    reactive enough. 76.

    Metallic bonds tend to form giant molecules but
    do not lend themselves to the creation of small
    molecules, which would be necessary for living
    tissue. Indeed covalent and bonds are critical in
    all life functions we know of. Fifty eight of
    the 76 remainders are metals, so we are left with
    18 stable nonmetals. When I am classifying these
    as non-metals, recall that I mean any material
    with any non-metallic properties.

    Break em down into classes of those which can form
    one bond, two, three and four:

    1 bond: hydrogen, fluorine, chlorine, bromine, iodine.

    2 bonds: oxygen, sulfur, selenium, tellurium

    3 bonds: boron, nitrogen, phosphorus, arsenic, antimony

    4 bonds: carbon, silicon, germanium, tin.

    The single bond atoms are pretty boring in the range
    of stuff they can do. They form diatomic molecules.
    Thats all. None are suitable for a basis for life.
    13 left.

    Oxygen doesn't form chains. Out. The other two-bond
    elements can form chains and rings, but if they do,
    they use up both of their bonds, so nothing else
    interesting can happen. So out with sulfur, selenium
    and tellurium based lifeforms.

    Then there were nine. Nitrogen tends to form super-stable
    diatomic molecules and do little else. Out. Of the
    eight remaining elements, only silicon and carbon are truly
    abundant in nature, with phosphorus a very distant third.
    Silicon has a number of interesting properties, but silicon-
    silicon bonds will not form when there is sufficient oxygen
    or hydrogen about, which explains why we see no silicon-
    silicon bonds anywhere in nature. The others remaining
    on the list are also much more fond of oxygen than they are
    each other, all except good old carbon.

    A carbon-oxygen bond is stronger than a carbon-carbon bond,
    but only slightly, 4 percent. So carbon *will* burn, if
    heated sufficiently. Good thing for us. So carbon will
    as soon form chains and rings with itself. Carbon is not
    just the best, it really is the only.

    I am deeply indebted to Isaac Asimov for the ideas in
    this analysis. He wrote an excellent essay on it over thirty
    years ago in Fact and Science Fiction, November 1972.

    Nowthen, we can talk about silicon lifeforms in the sense
    of uploaded minds running on a silicon-based computer,
    but these kinds of lifeforms do not evolve directly from
    non-living matter, but would rely upon carbon based life
    to get them started and perhaps to keep them going. If
    those carbon-based lifeforms are starved out early by
    the carbon being trapped in coal beds and oil fields
    before those same lifeforms figure out how to release
    it, then it is the end of the road for life on that
    planet. My claim is there simply is no substitute
    for carbon, no way to evolve around a shortage of it,
    no compensating for its scarcity. Carbon is the basic
    building block for everything that breathes or
    photosynthesizes, everywhere in the universe.

    To me this is the best explanation for the apparent
    radio silence in the galaxy: that in the overwhelming
    majority of cases, life on nearly every habitable planet
    comes in and goes out in a few billion years, never
    figuring out how to either metabolize or burn coal.
    Tech-capable intelligence is evidently a wacky anomaly.

    We made it. We are the few, the proud. Everyone wins
    as a result.

    spike

       



    This archive was generated by hypermail 2.1.5 : Thu Jul 24 2003 - 22:55:04 MDT