Post n. 9 English
Introduction
Iris Fly in
“L’origine della vita sulla terra” 2005, in the chapter “L’emergere della vita
né per caso né per disegno” writes: «[…] chance and telos the two horns of
a false dilemma , converge philosophically. The true conflict is between chance and intentionality
on the one hand and a physic-chemical process on the other hand»
That the
origin of life was a chance or the work of an Intelligent Design, is a just and
legitimate thought. The probable physic-chemical process, is however bogged
down by some trap which hides itself in the folds of this vision. Yet, behind
the shield of the difficulty of giving an exact definition of life, and behind
the shield of physical-chemical which cannot be excluded a priori, absurd
theories are often elaborated and without any data to sustain them. Certainly,
these also are legitimate, but they drag the argument too at length on
philosophical questions which often make one lose the central problem.
Life is ourselves, and is alive all that which
uses the same materials of which we are made. Life is ourselves, and is living
everything which is recognized as living today. Our object of study is the
origin of this life, and if someone has difficulty in recognizing a living
being, he may the ask a peasant.
However,
the old theories based on myths, dogmas and ideology have silenced some facts and generated
inexistent scenarios. In the end, extensive prejudices have transformed the
quagmire into a marsh. And then, to go out of the marsh and construct a new
theory it is necessary to make the last step: to open Pandora’s vase. We shall
extract many ashes, few certainties, and some questions, but hope itself will
come out. And one must be honest; if the physic-chemistry does not succeed in
giving explanations, it is best to admit it clearly because, as Paul Davies writes,
ignorance is a motivation for research much stronger than certitude.
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| digilander.iol.it |
Stephen J,
Gould, with reference to the contribution of chance in evolutionary processes,
coined an efficient metaphor: every repetition of the film of life would leave
evolution in a way very different from that taken in reality. We shall use this
metaphor to construct pieces of film to be put together at the end of our way.
That crazy
Empedocles: «[…]at the end, they say, he died by jumping into the Etna crater
to prove that he was a God. In the free interpretation of the poet Matthew
Arnold:
The great Empedocles, that ardent soul,
Jumping in to Etna, was entirely burned ».
(Bertrand Russell, Storia della
filosofia occidentale, 1° volume Filosofia Greca,1968).
During my
university studies, I made part of a group of friends fascinated by the Etna.
How many excursions and overnight stays and how many times we saw the lava
boiling in the central crater or running in torrents during the eruptions. But
I do not remember ever having seen little red men.
In the
debate opened already for a time, if life exists in space, a problem
immediately emerges: if there exists life in space, that is based on the same
chemical elements and the same organic substances? Or else there could be a
life very different from ours, that is based on different elements?
Iris Fly in
“L’origine della vita sulla terra” 2005, evokes the ideas of Shapiro and Feinberg. These
authors suggest that the definition of life should exist independent of local
characters of life on earth. They affirm that the life is the activity of the
system highly ordinated in matter and energy, characterized by complex
cycles which maintain or augment gradually the order. Life should hence be
innate inside matter. They affirm hence possible also a life founded on
silicates. In particular, because at 1000°C silicates become liquids, in a
planet near the sun or inside our planet, a life could have evolved founded on
silicates.
And if the
little red men had been seen by Empedocles
before burning!
Naturally
those who imagine completely different ambiances could not be lacking.
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| it.wikipepia.org/wiki Titano |
Titan
Saturn’s satellite, seems to have an ocean of liquid hydrocarbons at the
temperature of -180°C where islands of frozen water float. According to
Goldsmith on Titan could have evolved a life based on hydrocarbons.
We are life
and that which we recognize as living, and the almost totality of scientists
think that there cannot be an origin without atmosphere, energy and liquid
water. The facts which sustain such a hypothesis, studied by various
scientists, are so ample and consistent that they could be the subject of a
book. Serious arguments against this hypothesis are not known. Now, to propose
absurd scenes, without any scientific basis and then find an alibi behind the
usual passe-partout phrase “it is not possible to exclude such a possibility”
is not serous. It is like saying that the Lunatics inhabit the other side of
the moon so as to be invisible for the inhabitants of Earth.
Land, Air,
Fire and Water these are the four “elements” which mixing together can produce
the various complex substances which we find in the world. And hence also the
substances for the origin of life. But Empedocles with is four elements was
right? Also the land as he intended it,
that is like land masses, is indispensable to the origin of life? Or is it
possible that life can also surge on a planet yes rocky, but with his surface
completely covered with water more or less liquid?
It is
calculated that the galaxies in the universe are over 200
Milliards. Our galaxy contains 100 Milliards of stars. The number of planets in
the universe seems to be of the order of 1018. It is hence difficult
to think that Earth is the only planet which can bear life. As it has been
synthetically exposed in the precedent article A),
all the chemical elements were produced by evolution and by the collapse of the
massive stars. The final explosion of such stars has dispersed the elements
produced into space. Successive aggregations and reactions of such elements
they give origin to clouds of gas and dust which have given origin to solar systems.
Hence in a general line we can say that, all the solar systems of the universe,
have at their disposition the same chemical elements which life on our solar
system has had.
Yet, in
spite of having at disposition 92 natural chemical elements, living organisms
for the 96% of its weight uses only 4 of them: H (Hydrogen), O (Oxygen), N (Nitrogen),
C (Carbon), to which one must add small percentages of P (Phosphorus) and S
(Sulphur). Taken together
these 6 elements are called “biogenic elements”. They gives origin to all the fundamental
molecules of living matter. From the synthesis of these molecules have their
origin all the polymers necessary to the origin and the evolution of life.
But why
such a choice? And also, are other solutions possible?
We start
for the time being with the ascertainment that living organisms to carry out
their function need various stable and complex macromolecules.
The problem
was treated around the ´60’s by Wald, Calvin, Pauling and Coulson. A synthesis
of such works can be found in “Lezioni di Biofisica 3”, 1984 of Mario Ageno. Also Iris Fly “L’origine della vita sulla terra” 2005,
has amply treated the
argument quoting the work of Pauling, Fox and Dose, Gibor. From these two
essays come, in synthesis, the following conclusions.
According
to these researchers the biogenic elements present unique characteristics,
which renders them adaptable to take over the numerous biological functions in living organisms.
As known,
the electronic structures of the noble gases are, from an energy point of view,
less stable. Carbon, for example has 4 electrons in the second orbit whereas
Hydrogen has only 1 electron in the first orbit. When these elements link one
with another, they put together the electrons attaining the electronic
structure of the closest noble gas. These hence give origin to very stable bonds.
It is that which happens with methane, Carbon attains the stable configuration
of Ne (Neon) and Hydrogen the electronic configuration of He.
Another
reason is that these elements have very small atoms and when they link, their
interatomic distances are very reduced and the bonds stronger. This contributes
also to the stability of the compounds.
It is more over
necessary to add that Carbon has a unique property: its atoms can link one with another forming long chains more or
less ramified and ring structures. These linking with Hydrogen, or with
Hydrogen and Oxygen, or also with Hydrogen, Oxygen and Azote, give origin to an
enormous number (over a million) of compounds, which permit the great variety
of living organisms.
Carbon
besides can give origin also to double links or triple.
In the
economy of living organisms, the multiple bonds are very important because from
them it is possible to extract energy. In the double or triple bonds the second
and the triple bond are energetically weaker than a single bond. Hence when in
a reaction the second or the third bond is broken, to give origin to single
bond, much more stable, energy is liberated.
It has often been asked if
some other element could substitute carbon.
In the
periodic table of elements, Silicon (Si) is under Carbon and contains, like Carbon,
4 electrons in the last orbit which give origin to four bonds. Moreover Silicon
is an abundant element in the universe and in particular on our planet. It
realizes with Oxygen and with some metals such as Sodium (Na), Calcium (Ca);
Magnesium (Mg), Iron (Fe), and Aluminium (Al) a large number (thousands) of
various and complex compounds, which constitute over 90% of the Earth’s
surface.
But Silicon
can substitute Carbon?
Meanwhile
we can ascertain that the bond
C-C
Has a bond
energy of about 80 Kcal/Mole, whereas the bond
Si-Si
Is much
weaker, about 40 Kcal/Mole and hence the compounds of silicon are much less
stable.
Carbon
gives origin to hydrocarbons, compounds very stable of carbon and Hydrogen (CH4,
CH3-CH3, etc.) and Hydrocarbon chains are
incorporate in important compound for living organisms like the fatty acids. Also Silicon gives compounds with
Hydrogen, (SiH4, SiH3-SiH3, etc.), these
however are unstable, they flame spontaneously in air, they decompose in water
and they are no use for living organisms.
If we take
into consideration the two oxides CO2 and SiO2, the CO2
(Carbon dioxide) is a gas molecule which, with water and light, is used by the
photosynthetic organisms in the photosynthesis.
The SiO2, even if it is written in this way, in fact does not exist
as a molecule. The Silicon bonds with Oxygen forming solid polymeric structures
(Quartz), very hard which melt at high
temperature.
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| ww2.unime.it |
When one
writes the formula SiO2, one intends only the medium formula of
these polymeric structures. It is hence clear that the SiO2 could
never substitutes CO2. Silicon, like any other element, is unadapted
in the substitution of Carbon and it is impossible to understand in what planet
and under what ambiance conditions such organisms could function.
With reference to Silicon, Mario Ageno
(Lezioni di biofisica 3, 1984), adds: «[…] Silicon is completely unadapted as construction material for living organisms[…]».
In “Gli
elementi chimici della vita” Le Scienze ottobre 1972, and republished by Alessandro Minelli in “Gli albori della
vita”, Le Scienze 1984 Earl Frieden, at the point at which he treats the
assumptions of selection, affirms: «The second circumstance is linked to the
chemical properties of Carbon, the element which has been selected, by evolution,
in preference to Silicon».
This common
prejudice, which came out in those years, of wanting to extend evolution by
natural selection even to stones, contributes in creating a quagmire around the
problem of the origin of life, and it does not help Darwin’s theory.
But of what
evolution are we speaking? Here there has been no selection. Life, for its
origin, between Silicon and Carbon, has not had any choice: the passage was
obliged.
Studios,
than extended to Phosphorous and Sulphur, have shown how also the properties of
these elements are unique and hence they cannot be substituted by other
elements. Phosphorous, in particular, present characteristics both in the
construction of the nucleic acids and in the control
of energy transfers.
Hence we
can conclude that, because of the particularity of their atomic structure, the
biogenic elements are the only ones which, through their compound, are adapted
to carry out, in living organisms, the numerous biological functions. The
matter does not give us another solution: the passage was obliged.
On the
other hand, because the laws of physics and chemistry are universal if, given
some conditions, in other solar systems, life manifests itself, it uses the
same biogenic elements which are used by living organisms on Earth.
On our
planet.
About phosphorus!
As we have
seen in the last article (Prebiotic chemistry: rules or chaos, C), one thinks that in the prebiotic era the
concentration of phosphates, in waters, was like
the actual one, about 30µg/L (30 millionth grams for litre). That because one
esteems that at that epoch, in terms of acidity or basicity, the waters were as
now around neutrality, but at those times buffered by aluminium silicates,
produced on firm land by the cycle of water. In such conditions the minerals of
phosphorous of volcanic origin, the apatite, are
very little soluble.
The scarce
supply of phosphorous torments principally those who sustain the “RNA World”.
The nucleotides, constituents of the RNA contain
phosphorous and a low concentration of this element causes an insurmountable
limit to their vision of the origin of life on our planet. Because the apatite
are soluble in an acid ambience, to resolve the problem, Christian De Duve
(Polvere vitale, 1998) proposed that perhaps the primordial waters in which
life had its origin were acid waters. Other scientists have proposed the origin
of life near the volcanoes. We are still in the presence of ad hoc solutions, with ideas who have no
proof, localized and temporal in the end fortuitous.
However,
the problem of phosphorous, which came up between the supporters of the “RNA World”, remained on the whole
there, like one of the general difficulties for the origin of life and it has contributed
to increase the quagmire around the problem of the origin of life.
But can we
give a meaning to the fact that an element, the phosphorous, which controls the
energetic lever of living organisms, is present with an almost insignificant
concentration?
In other
words, the low concentration of phosphorous was a problem or an opportunity?
All modern
living organisms divide themselves in autotrophic and heterotrophic. The
autotrophic nourish themselves independently, like for example algae and green
plants, which starting from CO2, H2O and light synthesize
themselves the substances which they need. The heterotrophic nourish themselves
of autotrophic or of the alimentary chain which is generated by them.
Autotrophic and heterotrophic live together in a spectacular and harmonious
equilibrium.
But what
maintains this equilibrium?
Around the
years ’70 was unwittingly conducted an experiment almost planetary.
The
wellbeing that in those years, at least in the west, was consolidating in
society, caused an abundant use of synthetic detersives. To neutralize the
effect of Calcium and Magnesium contained in the water, and to increase its
rendering ,to soaps were added soluble phosphates. At that period the urban
wastes were canalized into lakes, into rivers and into the sea.
As we have said before, phosphorous is fundamental in reactions of energetic transfer it is the energetic lever of growth and evolution. What happened in those years? The phosphorous contained in the detersives breaks the equilibrium of the ecosystem.
The
excessive concentration of phosphorous, in particular in lakes, caused the
proliferation and growth of some types of weeds which invaded the whole ambiance.
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The
following development of micro weeds, caused the total consummation of oxygen
which caused the death of all fish. When the oxygen was consummated, the
processes of demolition caused the development of microorganisms which produced
methane and sulphuric acid. The phenomenon, called eutrophication, caused the
death of the lakes. Even if it was not true death. Life in the lake continued,
but it was a life almost exclusively of a vegetable type and anaerobic
microorganisms.
To observe
in that period the lake of Lugano was painful to all, but it was still more
painful for a chemist.
What
conclusions can we make from this experience?
It seems
that the low concentration of phosphorous is one of the factors which maintains
the equilibrium between living organisms at a planetary level. It slows down
the growth of the autotrophic, gives time to the heterotrophic to recuperate
the retard in nutrition, and forces all living organisms to have the same
starting tape for the evolution run.
And here,
it is fundamental to point out what was quoted by Stephen J. Gould and
Elisabeth S. Vrba in “Exaptation” 2008: «The development of the bones has been
an event of great importance in the evolution of the vertebrates. Without bones
vertebrates could not have later occupied firm land. […]. Pautard (1961,1962) has
observed that all the organisms who have much muscular activity need an escort
of phosphates accessible with a certain ease. […], Halstead (1969)suggested the
following scenario: the phosphates of Calcium, which deposit on the skin of the
first vertebrates, evolved at first as an adaptation to store the phosphates necessary for metabolic
activity. Only in a second period subsequent in evolution the bones substituted
the endoskeleton cartilaginous and assumed the function of support for which
they are today known. Hence, the bone has two principal functions:
support/protection and reserve/homeostasis (as reserve of some mineral ions,
including phosphates). […] According to Halstead’s analysis, the accumulation
of phosphates in the corporal tissues evolved at the beginning as an adaptation
for a function of warehousing and metabolic». Hence, in conclusion, the scarce
concentration of phosphates also generates strategies of survival which trigger
off colossal evolution processes.
Certainly
these conclusions need more confirmation. For the time being we have two facts which permit us to
extrapolate such consideration to the origin of life.
As we shall
see, during the prebiotic phase a great number of organic substances had their
origin, some of which had a high content of energy, and progressively
accumulated on the surface of the earth. It is logical to think that the first
living organisms were heterotrophic, that is they used these substances as
nutrition.
The
availability of phosphorous, on our planet must have been scarce already in the
prebiotic era. This to avoid, for the life which had just begun, that one or
few populations, more agile in taking possession of phosphorous, would acquire
an advantage invading the whole earth. Hence, probably, a problem phosphorous
never existed and the low concentration of phosphorous was an opportunity for
evolution.
And about silicon!
The unique
properties of the biogenic elements can give origin to an enormous number of
organic compounds and polymers necessary to the origin and to the evolution of life. During the
process of evolution of the living organism, life has however co-opted many
other elements present in the ambiance. The greater part of these elements has
the capacity of losing or gaining electrons, that is they become ions, and as
such they can be used. Among the elements co-opted there is also silicon, but
for marginal function like in diatom and in the bones and in the plumes of
volatiles.
The
exclusion of silicon seems incomprehensible if one takes count of the fact that
this element is abundant on our planet, and its compounds cover more than 90%
of the earth’s surface.
This question
was asked also by Earl Fieden (the article has been quoted): «If we pause on
the fact that silicon, over and above being second in abundance on the earth’s
surface, manifests an analogy with carbon in many chemical properties, it
appears rather difficult to understand the reason why evolution would have
completely excluded it from an essential biochemical function».
In the
meanwhile it is probable that Silicon was excluded just because of its
analogies with Carbon.
Silicon can
substitute Carbon, can bond with carbon atoms giving origin to compounds probable
of no use. Furthermore, to substitute a Silicon atom by a Carbon atom would have needed metabolic ways in addition and would have
complicated the evolution process.
However,
let us proceed with the observation of facts. What is truly today the rule of
Silicon, or rather of its compounds, in the general economy of life?
The
biogenic elements satisfy through their compounds all the needs of living
organisms. But life must put its feet somewhere.
Silicon
with its compounds, both on firm land and in the depths of lakes and seas,
creates the right ambiance to sustain life. No other element could substitute
silicon in this function.
Moreover,
as we have seen in the preceding point, the low concentration of phosphorous is
due to the aluminium silicates produced by the cycle of water which maintains
the pH (acidity-basicity) of seas and lakes around neutrality. Hence it is
probable that, indirectly, also the Silicon with is compounds, controls
evolution.
| palazzetti.it |
At last
Bernal’s theory on the origin of life, is based on Silicon compounds and in
particular on argil produced by alteration of the continental
rocks operated by water and by carbon
dioxide (CO2).
What can we
conclude?
Observation
seems to indicate a clear separation of roles: Carbon gives origin to the
compounds necessary to life, but it is Silicon through its compounds to sustain
to its origin and its evolution.
That crazy
Empedocles!
Turning back.
On our planet.
We can
conclude that, because of the particulars of their atomic structure, the
biogenic elements are the only which, through their compounds, are adapted to
carry out, in living organisms, the numerous biological functions. The matter does
not give us any other solution: the passage was obliged.
The
availability of phosphorous, on our planet must has been scarce already in the
prebiotic era, and it served to avoid, for life which had just emerged, that
one or a few populations, in some area of the planet, acquired an advantage
invading all the earth.
Between
Carbon and Silicon observation seems to indicate a clear separation of roles:
Carbon gives origin to the compounds necessary to the origin of life, but it is
Silicon through its compounds to sustain its origin and its evolution.
Hence, on
our planet, with reference to the biogenic elements and the Silicon, to their
concentration and to their roles, we can affirm that: if we rewind the film of
the origin of life and reproject it, with
every probability, we would see the same
story again.
In the universe
The
biogenic elements are the only ones which, through their compounds, are adapted
to execute, in living organisms, the numerous biologic functions: the passage
is obliged.
Because the
laws of physics and chemistry are universal and because the biogenic elements
are distributed in the whole universe, life can have had its origin anywhere
but, to manifest itself, it must wait
for adapted chemical-physical conditions.
We have no data
to enable us to affirm that in other planets the concentration of phosphorous is scarce as on the earth. Hence
it is probable that elsewhere, if life emerged, a higher concentration of this
element would have produced a different evolution.
Even if on
our plant it seems that the continents have had a role in the origin of life,
we do not have data to exclude that life could also emerge on a planet rocky
but with its surface completely covered with water more or less liquid.
Giovanni
Occhipinti
Translated by Silvia Occhipinti (10.03.2014)
Translated by Silvia Occhipinti (10.03.2014)
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