DNAunion: Stephen supplied some good material in relation to OOL and the
second law. I wish add to his. Here is a small snippet of some of my
personal notes that I just looked over yesterday (a work in progress, that
only gets updated once very six months or so!).
From my personal notes on the origin of life:
For useful work to be performed, more is needed than the mere bombardment of
Earth with solar energy - there must also exist some coupling mechanism to
properly "process" that energy. A coupling mechanism is an existing
intermediary that can harness and properly channel available energy in order
to accomplish useful work.
For example, take two calculators - one battery-powered and one
solar-powered. Take the batteries out of the battery-powered calculator, go
to the window, and calculate the square root of 1,048,576. Won't work. Now
take the solar-powered calculator to the same location and perform the same
calculation - you now receive the correct answer of 1,024. Both calculators
had the exact same amount of solar energy striking them, but only one of them
had a photovoltaic mechanism (coupling mechanism) that allowed it to channel
that energy into accomplishing a useful purpose (in a similar manner, we
humans cannot produce sugars from the Sun's rays because we lack the
photosynthetic mechanisms found in plants). Now, reinsert the batteries into
the battery-powered calculator and tape the same number and type of batteries
to the solar one. Next, go to an "absolutely" dark location (like a closet)
and try to calculate 2^13. This time, even though both calculators had the
same amount of energy at their disposal (both had the same number and type of
batteries) only the battery-powered calculator was able to accomplish the
task because only it had the mechanisms required to make use of the available
energy. The two calculators can channel available energy to accomplish
meaningful work only if the appropriate coupling mechanisms already exist and
are present. In addition, each calculator has its own particular coupling
mechanism and can use only a specific kind of energy, which is, of course,
dictated by its particular coupling mechanism.
As a generalized example, just providing undirected energy (chemical,
thermal, kinetic, or nuclear; say dynamite, blow torch, sledge hammer, or
radiation respectively) to a pile of bricks will not produce a building. As
in the calculator example, a coupling mechanism is needed to direct the flow
of energy - in this case, humans function as the coupling mechanism. They
decrease entropy (disorder) by properly channeling energy to produce a
more-ordered arrangement of components (the final product, a building, is
more ordered than the individual building blocks from which it was
constructed).
Photosynthesis (need for coupling mechanisms)
The primary argument against the possible thermodynamic problems of the
origin of life has been that the Earth is an open system, receiving the
energy input from the Sun needed to decrease local entropy - as associated
with organic complexification. Therefore, the obvious process to examine is
photosynthesis, in a prebiotic context. Does photosynthesis need a coupling
mechanism? Yes.
"Even if we assume the existence of some [primitive] membrane-bound
light-trapping system, we still have to account for the channeling of the
trapped energy into productive chemical processes, rather than useless heat."
(Vital Dust: Life as a Cosmic Imperative, Christian de Duve, Basic Books,
1995, p35)
In photosynthesis, chlorophyll is the primary molecule that drives uphill
(thermodynamically unfavorable) reactions.
"But, as demanded by the Second Law, the spinach has to work for it. Or,
rather, it makes the energy of the sun work for it. Chlorophyll, the green
stuff of plants, does exactly that. It uses the energy of sunlight to tear
off hydrogen from water and lift it to a high enough level of energy so that
the hydrogen can, in turn, tear off the oxygen from carbon dioxide and
nitrate and replace it…" (Vital Dust: Life as a Cosmic Imperative, Christian
de Duve, Basic Books, 1995, p36).
However, this photosynthetic coupling mechanism (chlorophyll) is too complex
to have formed spontaneously, and even then, chlorophyll functions as only
one part of a system (so the other components would also need to have been
formed naturally).
"Chlorophyll is a very complex molecule, which, in addition, has to be
associated with other complex molecules embedded in a membrane to do its job.
It is highly unlikely that such a system could have arisen spontaneously in
early prebiotic days." (Vital Dust: Life as a Cosmic Imperative, Christian de
Duve, Basic Books, 1995, p36)
In addition, not every form of chlorophyll can perform the vital energy
processing function, so not just "any old" chlorophyll would suffice.
"Moreover, only specific forms of chlorophyll can pass a photoexcited
electron to another molecule in an oxidation-reduction reaction that traps
light energy and converts it to chemical energy." (Wayne Becker, Jane Reece,
Martin Poenie, The World of the Cell, Third Edition, Benjamin/Cummings
Publishing Company, 1996, p379)
One of the primary structural components of chlorophyll is its porphyrin
ring, which is a complex ring-shaped organic molecule that, in this case,
binds a magnesium ion (Mg2+ - a divalent cation).
"The magnesium ion (Mg2+) in the chlorophyll molecule affects the electron
distribution in the porphyrin ring of the molecules, ensuring that a variety
of higher-energy orbitals are available and that more than a few specific
wavelengths of light can be absorbed." (Wayne Becker, Jane Reece, Martin
Poenie, The World of the Cell, Third Edition, Benjamin/Cummings Publishing
Company, 1996, p379)
As a reminder, porphyrins have thus far not been created under plausible
prebiotic conditions.
"Some important biological compounds that could not be synthesized under
prebiotic conditions include several amino acids (arginine, lysine, and
histidine), porphyrins, and riboflavin (Miller, 1992)." (Noam Lahav,
Biogenesis: Theories of Life's Origins, Oxford University Press, 1999, p167)
All of this seems to suggest that the argument based upon open-system
thermodynamics involving the Sun fails because of the lack of an appropriate
prebiotic coupling mechanism required to capture and properly channel the
Sun's energy input into producing useful "biological" work.
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