I believe (hope) I'm using the term primordial soup as its used
in the literature. Normally this refers to a dilute "broth" of
organic chemicals in the earth's early ocean. For example:
< It was therefore possible for many different reaction products, of
< high and of low molecular weight, to form and to accumulate in
< large quantities in the oceans.
< -- Manfred Eigen, _Steps Towrds Life_, Oxford University Press,
< 1992, p. 32
One also hears about soups in tidal basins, lagoons, beaches etc.
but this is almost always in the context of a soup in the
ocean.
Now, what evidence is there that this soup ever existed?
First, laboratory syntheses, no matter how nice they may be,
do not provide evidence for the existence of a primordial soup.
According Dr. Soup himself ;-), Cyril Ponnamperuma,
< The laboratory studies have established that the molecules
< necessary for life can be made in the labratory. A question
< of paramount importance is whether this process did indeed
< take place on the earth or elsewhere in the universe. Can
< we go back in time to the earliest stages of the earth, of
< the solar system, and dig up some evidence for the presence
< of prebiologically synthesized organic molecules? Many
< attempts have been made to resolve this problem. ...
< -- Cyril Ponnamperuma, "Cosmochemistry and the Origin of
< Life", in _Cosmochemistry and the Origin of Life_,
< C. Ponnamperuma ed., D. Reidel, 1983, pp. 1-34.
--------------------------------------------------------
< Concepts dealing with the origin of life are mainly derived from
< simulation experiments carried out in the laboratory. Such
< experiments are a help in elucidating the mechanisms and processes
< that were possibly involved in the formation of the first organism.
< However, experiments cannot answer the question as to where and
< when that event took place. This is a historical phenomenom and
< therefore can only be traced in the historical record as preserved
< in ancient rocks.
< -- Hans Pflug, "Early Geological Record and the Origin of Life,"
< _Naturwissenschaften_, 71:63-68, 1984.
---------------------------------------------------------
And what do the ancient rocks tell us?
< Now if we assume that a primitive organic soup was first
< formed as a precursor requirement for the living system
< and that it formed and accumulated organic matter over
< millions of years, then there should be evidence for such
< matter in the earliest of sediments. Thus the "primitive
< soup" would of necessity have to contain large amounts
< of highly nitrogeneous matter, especially amino acids and
< purines and pyrimidines. Such compounds, let alone nucleotides
< or polymers thereof, are extremely readily absorbed on a
< variety of rock and clay particles. In a primeval ocean
< therefore we would expect these concentrated organic soups
< to deposit their organic matter in the form of massive
< sediments over millions of years. These sediments would
< undoubtedly undergo exposure to many extremes of temperature
< and pressure. When materials such as simple non-nitrogenous
< compounds are heated and compressed they will generally
< finish up as carbon, but highly nitrogenous materials when
< subjected to extremes of temperature form nitrogenous cokes--
< graphite-like materials containing large amounts of nitrogen.
< If there ever was a primitive soup, then we would expect to
< find at least somewhere on this planet either massive
< sediments containing enormous amounts of the various
< nitrogenous organic compounds, amino acids, purines, pyrimidines
< and the like, or alternatively in much metamorphosed sediments
< we should find vast amounts of nitrogenous cokes. In fact no
< such materials have been found anywhere on earth. Indeed to
< the contrary, the very oldest sediments, ranging to something
< like 3.7x10^9 years and consequently very close to the basement
< figure 4.0x10^9 years mentioned earlier, contain organic matter
< very much of the sporopollenin-type (Chapter 10) and degradation
< products of such materials, especially a variety of alkanes
< and fatty acids and derivatives. Sediments of this type are
< extremely short of nitrogen. Some idea of the sparseness of
< nitrogen comes for example from the observation of Schopf
< that extraction of Precambrian sediments with 0.5N ammonium
< acetate provided only nanomolecular (10^-9) amounts of amino
< acids, mainly glycine. Whether of course the glycine was derived
< from the ammonium acetate is another matter. Either way these
< and other experiments have served to emphasize the scarcity
< of either chemicals such as amino acids or of nitrogenous
< cokes in ancient sediments or in nearby metamorphosed rocks.
< There is, in other words, pretty good negative evidence that
< there never was a primitive organic soup on this planet that
< could have lasted but for a brief moment.
< -- J. Brooks and G. Shaw, _Origin and Development of Living
< Systems_, Academic Press, 1973, p. 359.
---------------------------------------------
< Would there not be geological evidence in rocks of 4 to
< 3.8 billion years old, if there had been such a soup?
< The space science studies board believes there should be:
< '_These speculations on chemical evolution, multiple
< origins of life, and models of early environmental
< conditions in the atmosphere and oceans can only be
< substantiated by the geological record_.' What testimony
< would have been left behind by the primeval soup in the
< sedimentary rocks? We can learn this directly from the
< work of those scientists who take the primeval soup for
< granted. All methods of simulating the formation of
< amino acids and other 'building blocks' leave a tarry
< polymeric material as their most abundant product. Carbon
< that was once composed of living matter is slightly
< enriched in 12^C. No chemical reaction, heat, pressure
< or other treatment to which these ancient rocks may have
< been subjected can change one of these isotopes to
< another. Thus the carbon isotope ratio is a reliable and
< indestructable fingerprint to determine whether carbonaceous
< material, including kerogen, came from living organisms
< or by inorganic chemistry from a primordial carbon source.
< Sedimentary rocks at Isua in Greenland have been dated at
< 3.8 billion years ago, a time near the end of the late
< heavy bombardment. They do indeed contain kerogen.
< Schidlowski reported that all carbon in these rocks divides
< distinctly into two groups, one high in 13^C and one depleted
< in 13^C, with respect to the isotope ratio found in
< atmospheric carbon dioxide. The kerogen of the very old
< Isua rocks is depleted in 13^C. This is just what would
< be expected if the kerogen had been derived from cyano-
< bacteria-like microorganisms capable of photosynthesis
< of carbon dioxide and nitrogen by means of an enzyme
< system to form living matter.
<
< According to the standard model for the origin of life,
< there are two paths the carbon would follow in the
< primeval soup. The first is toward forming the ancient
< protobiont, the remains of which would go to kerogen.
< The second, and the much more abundant amount, is the
< tarry material generated in all origin-of-life simulation
< experiments. No kerogen from the tarry material left over
< from the generation of the 'building blocks' of life is
< found. This is extremely good confirmation that there
< never were the large quantities of dissolved amino acids,
< or other 'building blocks', that could be called a primeval
< soup. The significance of the very old kerogen in the Isua
< rocks in Greenland is that there never was a primeval soup
< and that living matter must have existed abundantly on Earth
< before 3.8 billion years ago.
< -- H.P. Yockey, "Information in bits and bytes",
< _BioEssays_, vol. 17, no. 1, 1995, pp. 85-88.
---------------------------------------------------
I would like to preface the following quote by saying that
Stanley Miller is one of my all time favorite scientists,
thus I find it hard to be critical of him. One reason I
say this is that Miller himself performed many of the
experiments which greatly undermine his own favored senario
for the origin of life. Nevertheless, I think he really
botches with the following reasoning:
< Proposed atmospheres and the reasons given to favor them are not
< discussed here. As described below, the more reducing atmospheres
< favor the synthesis of organic compounds in terms of both yields
< the variety of compounds obtained. Some of the organic chemistry
< can give explicit predictions about atmospheric constituents. Such
< considerations cannot prove that the earth had a certain primitive
< atmosphere, but the prebiotic synthesis constraints should be a
< major consideration.
< -- Stanley Miller, "Which Organic Compounds Could Have Occurred
< on the Prebiotic Earth?", Cold Spring Harbor Symposia on
< Quantitative Biology, Volume LII, pp 17-27.
----------------------------------------------------------
The fact that certain prebiotic syntheses require a certain type
of atmosphere provides no evidence whatsoever regarding what the
primitive atmosphere actually was like. Instead, independent
evidence strongly suggests that the required atmosphere was not
present. Thus Miller's constraints on prebiotic synthesis are not
met, thus ...
Brian Harper
Associate Professor
Applied Mechanics
The Ohio State University
"Because there's no primordial soup;
we all know that, right?" -- Leo Buss