Post n. 9 English
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.
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.
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!
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
Has a bond energy of about 80 Kcal/Mole, whereas the bond
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.
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.
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.
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.
That crazy Empedocles!
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.
Translated by Silvia Occhipinti (10.03.2014)
Translated by Silvia Occhipinti (10.03.2014)