There is a
further possibility which is not really a source of energy but which would have an
important impact on whether or not the minimum energy of activation was achieved in a,
heretofore, non-spontaneous, endogonic set of molecules. This additional candidate
concerns the process of catalysis.
"A
catalyst is capable of helping reactions to proceed by, among other things, helping to
lower the normal, minimal level of energy which usually needs to be imported in order to
activate a given chemical reaction. A wide variety of non-protein, non-enzymatic
mechanisms, ranging from clays, to metal ions, to RNA, have been proposed as possible
catalytic agents in a prebiotic environment.
"Since,
previously, I already have given something of a taste for what is possible,
experimentally, with the electrical discharges of Miller's experiment, and the anhydrous,
heat driven experiments of Fox, I would like to touch on a few of the other possibilities.
Once again, this treatment won't be exhaustive, but it will provide members of the jury
with a framework of sorts through which to understand this aspect of the evolutionary
model.
"There
have been a number of laboratory experiments which explored certain aspects of the
phenomenon of shock waves. For instance, the heat, in the vicinity of 3000 degrees Kelvin
or more, that is generated by rapidly expanding gases in shock wave tubes, has been used
to produce such hydrocarbons as hydrogen cyanide and amino acids in different kinds of gas
mixtures with reducing properties.
"A few
researchers have hypothesized that organic compounds may have been synthesized in the
atmosphere when meteors passed by and, in the process, created conditions similar to the
shock heating experiments in the laboratory. After being synthesized, these compounds
would have found their way, through one means or another, to the ocean.
"Once
in the ocean, one of three things are likely to have occurred. The newly synthesized
molecules would have reacted further with molecules in the ocean; or, these molecules
would have been carried to tidal pools and other intertidal zones where they would become
concentrated and readied for further reactions when the water in these pools and zones
evaporated; or, some combination of the first two possibilities.
"Some
scientists have calculated that meteors with a mass between 10-14 to 102
grams enter the Earth's atmosphere with sufficient frequency to deliver about 1.6 x 107
kilograms of mass to the Earth each year. If one were to assume these meteors traveled
with a velocity of 15 kilometers per second, the meteors collectively generate about 1.8 x
1015 joules of energy per year, which is equivalent to many megatons of
explosives.
"Ah ...
Professor, before you continue," Mr. Mayfield interrupted, "could you explain
what a joule is."
"A
joule," Dr. Yardley explained, "is a unit of energy equivalent to the amount of
work which can be done, or the heat generated, in one second, by an electric current of
one ampere against a resistance of one ohm and ...." Stopping, Professor Yardley
smiled sheepishly and raised his eyebrows somewhat. "Sorry," he said, "I
don't think my answer is quite what you were looking for, Mr. Mayfield."
After
thinking about the matter for a few seconds, the professor informed the lawyer: "The
easiest, maybe most recognizable, thing to say," he offered, "is this. A watt of
energy is equivalent to 1 joule per second. However, one should keep in mind that,
strictly speaking, a watt is a measure of power, whereas a joule is a measure of energy.
Power deals with the rate at which energy is expended."
Dr. Yardley
looked at the prosecution lawyer with a more hopeful expression, seeking, apparently,
acceptance for his new approach. When Mr. Mayfield motioned his head and made a face, both
of which seemed to suggest: 'why don't we move along before things get worse', Dr. Yardley
returned to his testimony concerning the energy created by atmospheric shock waves.
"100
percent of the kinetic energy of meteorites of the previously indicated size is lost to
the atmosphere. Researchers maintain that some fraction of this energy is converted into
the generation of atmospheric shock waves. Estimates of the fraction of the energy being
converted in this manner run from 30% downward.
"Working
along similar lines, researchers have made calculations for the amount of energy which is
converted to shock waves for other kinds of phenomena. For example, the airbursts of
carbonaceous chondrites with a radius which is less than, or equal to, 300 meters, is
believed to generate about 1.5 x 1014 joules of energy per year, which is the
equivalent of a huge amount of high explosives.
"When a
meteorite does not airburst and strikes the ground, if the meteorite is sufficiently big
in size, it will generate a post-impact vapor plume. Some researchers have calculated that
such post-impact vapor plumes could generate as much energy as 6 x 1017 joules
per year in the form of shock waves which, once again, would be the equivalent of many
megatons of high explosives.
"In
addition to the energy being converted into shock waves capable of synthesizing certain
organic molecules, researchers have estimated that a small percentage of the carbon in the
meteorite will be incorporated into organic compounds when the meteorite vaporizes upon
impact. This percentage is considered to be about 4%, which would have yielded
approximately 4.6 x 106 kilograms of organic materials per year on prebiotic
Earth.
"Most
of this incorporated carbon shows up in the form of carbon dioxide and carbon monoxide.
Nonetheless, several percent of the carbon is incorporated into various kinds of
hydrocarbons, with a still smaller percentage being converted into such compounds as
hydrogen cyanide, as well as aldehydes, like formaldehyde.
"If one
adds all of these different kinds of energy and mass values together, one can begin to
develop a thermochemical model of shock synthesis under both reducing and relatively
neutral atmospheric conditions. Scientists have discovered that the efficiency with which
organic compounds can be synthesized through shock waves is very dependent on the
compositional character of the atmosphere in which the shock wave occurs.
"For
example, in a reducing atmosphere of methane, nitrogen and water vapor, for each joule of
energy generated by shock waves, one can produce approximately 1017.5 molecules
of hydrogen cyanide. Simultaneously, a lesser amount of simple hydrocarbons like C2H2,
C2H4 and carbon soot also will be produced.
"After
all the calculations are done, this works out to be a yield of 1.2 x 10-8
kilograms of organic material is generated for each joule of shock-created energy in a
reducing atmosphere. In a neutral atmosphere, on the other hand, consisting of carbon
dioxide, nitrogen and water vapor, a yield of 2.5 x 10-16 kilograms of hydrogen
cyanide is produced for each joule of energy, but yields of formaldehyde (H2CO)
remain roughly equivalent to what occurs in a reducing atmosphere.
"Similar
calculations have been carried out in relation to both lightening and coronal discharges
in the atmosphere. For example, in a reducing atmosphere, lightening is estimated to have
been likely to generate 3 x 109 kilograms per year of organic material from the
1 x 1018 joules per year of energy created.
"In a
neutral atmosphere, lightening is calculated to have been likely to produce 3 x 107
kilograms of organic material per year from the same amount of energy yields. However, as
the atmospheric ratio of hydrogen gas relative to carbon dioxide drops from, say, 2 down
to 0.1, the yield of hydrogen cyanide, formaldehyde and amino acids drops by a factor of
several magnitudes or powers of ten.
"If one
combines all the different ways of using energy which would have been available on
prebiotic Earth to generate organic materials, scientists estimate that about 1011
kilograms of organic material would have been produced each year in a reducing atmosphere.
However, in a relatively neutral atmosphere, consisting of mostly carbon dioxide and about
10% hydrogen gas, approximately 109 kilograms of organic materials would have
been produced each year, but this yield will fall considerably as the relative percentage
of hydrogen gas drops.
"In the
light of these calculations, evolutionary scientists have come to the following
conclusion. If all the organic materials produced by these various means were fully
soluble in oceans comparable in extent and depth to our present oceans, and if these
organic materials had a mean lifetime of approximately 107 years with respect
to thermal degradation in relation to mid-ocean hydrothermal vents, then the steady-state
equilibrium of organic materials in prebiotic times would have been about 10-6
grams of organic solute for each gram of ocean water in a neutral atmosphere, and
approximately 10-3 grams of organic solute for each gram of ocean water in a
reducing atmosphere.
"Modern
researchers in evolutionary theory believe that if the early Archean era atmosphere were
strongly reducing in character, the predominant method of generating organic materials may
have been through shock waves. Lightening would have been considerably less predominant in
its effects in this regard, and the roles of ionizing radiation and radioactive
disintegration would have been quite negligible."
"So,"
said Mr. Mayfield, "if someone wanted to put all of this information into perspective
in a relatively simple manner, what would be the bottom line?"
"I
guess," replied Professor after a few seconds hesitation, "one should return to
the scenario I outlined earlier. Moreover, for the sake of simplicity, let's concentrate
on just one of the hydrocarbons, namely hydrogen cyanide, that is likely to have been
produced by one, or more, of the energy sources about which I have been talking.
"First,
energy from shock waves or lightening or ultraviolet radiation is coupled with atmospheric
gases such as methane (CH4), ammonia (NH3), and hydrogen (H2),
all of which serve as reducing agents, giving up hydrogen atoms or electrons to other
substances. This coupling leads to the production of hydrogen cyanide.
"Secondly,
the HCN or hydrogen cyanide that is formed becomes dissolved in water vapor in the
atmosphere. Eventually, this becomes precipitation or rain which falls into the ocean.
"Thirdly,
once in the ocean, the hydrogen cyanide would oligomerize or gather together in small
quantities here and there. These oligomers of HCN would then undergo hydrolysis in the
ocean.
"Hydrolysis
is a process in which water interacts with a substance and tends to separate out the atoms
of a substance such as hydrogen cyanide (HCN) by hydrating them, that is, surrounding them
with water molecules. Furthermore, since water is a polar molecule involving, as
previously indicated, dipolar regions of electronegative and electropositive charge, the
polar character of water combines with the atoms which are being separated out through the
process of hydrolysis to recombine to form different kinds of molecules.
"For
instance, just to give you some idea of what is being said here, suppose one had a
one-liter solution of one-tenth molar concentration of hydrogen cyanide and left it for a
year. As a result of hydrolysis, after one year, one would find quite tiny, but
detectable, amounts of the purine nucleic base adenine as well as larger, but still very
small, quantities of the amino acid glycine.
"If we
project such liter-size processes into the context of the trillions and trillions of
liters of the oceans of the world, and if we left things for millions of years rather than
one year, we are very likely to discover substantial amounts of a wide variety of complex
hydrocarbons, many of which probably will be of fundamental importance to issues
concerning the origins of life."
