Phenomena of Nature: Chemical Evolution – Dr. Sayed Abdul Wadud
“He Who created you from inorganic matter”.
Composition of the Stars and Planets. A star is a globe of incandescent gas. It may be assumed that a star condenses out of interstellar material which is mainly hydrogen. As it contracts and the internal temperature rises, nuclear reactions begin. As stated earlier, the hydrogen nuclei fuse to form helium nuclei with a slight loss of mass and release of energy. The supply of hydrogen being not inexhaustible, drastic changes take place eventually. There are two distinct types of stellar population. Population I, consists pre-dominantly of very hot bluish or white stars, as well as interstellar gas and dust. Population II, the brightest stars are red giants with little interstellar material. Red stars are later stage of evolution. Here the interstellar material has been used up in the formation of fresh stars. It is suggested that with the passage of time, the sun will become a red star of larger diameter and greater luminosity than at present so that earth will become too hot to support life. At a still later stage this may be followed up by a rapid collapse of the sun into a very small dense star, radiating feebly because of continued gravitational contraction, like the companion of Sirius (double star).
Solar System. As already noted in Chapter II, several hypotheses concerning the origin of solar system have been proposed, such as Nebular hypothesis of Laplace, the Planetesimal hypothesis, the Tidal Disruption theory of Jeans and Jeffreys. The view now widely accepted is that the solar system is the result of excessive rotation of a gaseous ball which was made up of free atoms. Hydrogen atoms were probably more abundant and the other heavier types were present in lesser quantities. The sun was formed when most of the atomic gas, hence most of the hydrogen, gravitated towards the center of the ball. Even today the sun is composed mostly of hydrogen atoms. A swirling belt of gas remained outside. Eddies formed in this belt and in the course of time it broke up into a few smaller clouds. These spinning spheres of glowing gaseous clouds were probably the early planets.
THE STORY OF
Chemical Evolution on the Earth (in relation to the Appearance of Life).
Thus to begin with, the Earth was probably a glowing mass of free hydrogen and other types of atoms, which eventually became sorted out according to weight Heavy ones such as Iron and Nickel settled down in the center of the Earth where they are still present. lighter atoms such as Silicon and Aluminium formed a middle layer. The very lightest such as Hydrogen, Nitrogen, Oxygen an Carbon, collected , collected in the outermost layer (Fig. 13).
|fig. 13.—the eLEMENTS COMPOSING THE EARTH
The elements became sorted out according to weight. Heaviest ones sank into the centre, relatively light ones formed the middle shell and extremely light ones formed the outer shell.
Temperatures must have been too high in the beginning for atoms to become linked together in the form of stable compounds, as the bonds would have been broken as fast as they might have formed, but under the influence of the cold of cosmic space, the earth began to cool down gradually. With the passage of time as the temperature of the earth became low enough, relatively stable compounds came into existence. Compounds thus formed multiplied and free atoms disappeared.
As noted above, the outer layer of the gaseous ball that made the early earth consisted mainly of Hydrogen, Oxygen, Nitrogen and Carbon atoms. As it cooled down enough to allow the formation of compounds, these four types of atoms played an outstanding role. As a result, even today 95% or so of the substance of all living matter consists of just these 4 elements.
On the basis of their known chemical properties, these elements presumably became linked into some half a dozen compounds as below:
The first three of these compounds came into existence not only on the Earth but on the other planets as well. For example, enormous amounts of water, methane and ammonia of undoubtedly abiogenic origin, are present today on the surface of the planet Jupiter in the form of thick permanently frozen solids. Methane and ammonia are also present on Saturn, Uranus and Neptune. Apparently these compounds must have been formed there as on Earth, but being too far away from the sun the surfaces of these planets probably froze before any further bonds could possibly occur. On the hot earth, however, the early compounds could interact further and give rise to new compounds later on.
Origin of First Mountain Ranges and Collection of First Compounds in Sea Water. As the hot gas ball of the Earth, gradually cooled down temperatures became low enough to allow some of the gases to liquefy and some of the liquids in turn to solidify. While passing from the liquid to the solid state, the very dense solids, like iron and nickel, sank into the liquid and as stated already, settled down in the center of the earth; while others floated like great icebergs, some sticking out of the liquid higher than the others, like cork and wood floating in the water because of the specific gravity being different in each case (Fig.l4a). We know that the earth’s crust is composed chiefly of two kinds of rocks, known as granite and basalt. The granite with a specific gravity of 2.7 and the basalt with a specific gravity of 3.0, both floated in the liquid earth mass whose specific gravity was 5.7. But granite stuck out further like cork in water while basalt floated like wood (Fig.l4b). Consequently, when the entire surface had cooled down to a solid, it must have been irregular, with
Fig.l46.”Masses of Canaanite and Basalt floating in liquid rock or Magma.
granite standing higher than the basalt. Thus the middle shell of lighter substances in the gas ball of the earth (Fig. 13) gradually solidified to become the earth’s crust, and the wrinkles and folds so formed gave rise to first mountain ranges. Surrounding this crust was the outer atmospheric covering which at temperatures then prevailing still remained gaseous. Up to this stage water was only present in the atmosphere in the form of clouds which surrounded the earth’s crust, for probably hundreds of miles above its surface. As the temperature of the solid earth underneath was too high, water could not stay there in liquid form. As soon as it touched the surface of the earth, it evaporated immediately. But as the earth’s crust became cool enough to allow liquid water to stay on, rains started. There was a continuous downpour for hundreds of years. Rivers flowed down from the heights of early mountains and water collected in the depressed areas to form the early seas (Fig. 14c). Atmospheric gases-methane, ammonia, carbon, dioxide and hydrogen cyanide-were washed down from the atmosphere into oceans. Salts and minerals also collected in the ocean water. These were obtained from three different sources, firstly from the land surfaces brought down by the rivers, secondly from the sea-shores, dissolved by the violent tides, thirdly from the Fig. 14c. “Early seas formed over basalt interior of the earth brought by
the molten lava bursting into the seas. This dissolving of gases and minerals into the ocean water was an important event with regard to the origin of life on the Earth.
ROLE OF FIRST COMPOUNDS IN THE ORIGIN OF LIFE
Role of Water. Life is not possible without water and water has always been the most important single component of living matter. It makes 60 to 90 per cent of the weight of living organisms, being more abundant in young cells or young organisms than the older ones, and in lower aquatic animals than in higher terrestrial types. Three-fourths of the earths surface today is covered with water and this is of great importance in the economy of living objects. It plays a fundamental role in life (a) in its being the best solvent for inorganic substances and for many organic compounds; (b) it favours the dissociation of electrolytes dissolved in it; (c) it has high surface tension; (d) it has got great fluidity; (e) it has a great capacity to absorb heat. It is thus an excellent medium for chemical reactions to take place. Moreover water was originally the only good source of hydrogen and oxygen. Both of these elements form the basis of building material of living bodies. But as noted already, free atoms of hydrogen and oxygen became unavailable soon after the origin of the earth. Water molecules then became the chief source of supply of these atoms. Even today water is the only usable source of hydrogen and one of the important sources of oxygen. Water thus took the role of a key which opened the door to life. The gases and minerals dissolved in the ocean water reacted with each other and with the water itself to form the early organic compounds and the subsequent chemical evolution led to the emergence of most complex organic compounds which became the precursors of the units of life. The point shall be amply illustrated in the following pages. After the life started on the earth, water still maintained its fundamental role in its control.
The Holy Quran says:-
“And We made from water everything living”.
“And He kept His control post (of life) on water”.
Role of carbon. The chief actor on the stage of life set by water was Carbon which is a versatile element, with convalence of four, i.e., it can link with four atoms of same or of different kinds. Apart from this, carbon atoms may link up directly to other carbon atoms to form chains of varying lengths. Such as: But these are not open chains, they form parts or fractions of whole molecules in which various other atoms or groups of atoms are attached to the carbon. For example if carbons of two or more methane molecules are joined into a chain, their hydrogen atoms will be bonded to carbon as follows:-
No other element approaches the self bonding capacity displayed by carbon.1” The compounds like methane in the early oceans must have reacted with other compounds present there, giving rise to a large variety of carbon containing compounds. This happened to be a very important event in the evolutionary history of living matter, because carbon compounds provided the basis for the synthesis of numerous molecules which constituted the structural framework of living bodies, the carbon compounds are thus known as Organic Compounds.
‘Silicon can do this but only up to a limited degree. It can, however, give huge structures when bonded through oxygen atoms as: But silicon is not found intensively in living organisms.
COMPOUNDS OF CARBON
Among the numerous organic molecules which came into existence in the early seas, five categories became especially significant from the point of view of later developments
These are (1) Sugars (2) Glycerines (3) Fatty acids (4) Amino acids and (5) Nitrogen bases. The structural make up of these compounds is shown in (Fig. 15). Note that in each case a carbon skeleton, either a chain or a ring, forms the basis of the compound and that various group patterns of hydrogen, oxygen and nitrogen are linked to it.
- Sugar. — Sugars are short chains of carbon; 6 or 6 are common in organic matter. Other elements are H and 0. Sugars with five carbons are Pentose, those with 6 carbons are Hexose.
- Glycerines. – Glycerines are chains of three carbon atoms. Other elements are same as in sugars, i.e, H and 0.
- Fatty Acids. – Fatty acids are chains of carbon atoms 2-20, other atoms are H and 0. Carboxyl group COOH is at the end
- Amino Acids. – They also contain COOH group. In addition contain NH2 (amino group). Both groups are attached to carbon; also attached is a carbon skeleton (R) which varies in structure considerably.
- Nitrogen Bases. – There are two major sub-groups, PURINES and PYRIMTOINES. Both contain ring structures of C and N; ring being single in pyrimidines and double in purines.
Sugars. Here carbon skeleton is a short chain which has five or six carbon atoms and they are particularly common in living matter. C5 sugar is called Pentose, an important example is ribose (C5H10O5 ). C6 sugar is called Hexose, example is glucose (C5H10O5 ). In sugars as in other carbohydrates the only elements attached to carbon are hydrogen and oxygen.
Glycerines. Also contain the same elements as sugar i.e., Carbon, Hydrogen, and Oxygen; but contain three carbon atoms in a chain.
Fatty acid. They also contain the same three elements as sugar and glycerine but carbon chain may vary from 2-20 or even more atoms. One end of a fatty acid molecule always terminates in COOH group called the carboxyl group which gives the molecule its acid properties.
Amino-Acids. Like other acids they also contain carboxyl group and in addition carry NH2 or amino group. Both the carboxyl and amino groups are bonded to a carbon atom. To this atom is also attached a chain or ring of carbon skeleton.
Nitrogen bases. Nitrogen is also invariably present in Nitrogen bases which include two major groups Pyrimidines and the Purines. In both of them the molecular skeleton is always a ring containing carbon as well as nitrogen atoms, the ring being single in Pyrimidines and double in Purines.
Under conditions that prevailed in the primitive earth and on the basis of structural configurations it is presumed that the above five categories of organic compounds might have been formed as follows:-
Presence of cyanide could have provided useful material for Carbon and Nitrogen Rings.
Oparin in his book, ‘The Origin of Life’ proposed that earth in its early stages had a reducing atmosphere of Methane, Ammonia, Water and Hydrogen, and that organic compounds might be formed under these conditions. The hypothesis was accepted and followed successively by famous scientists like Urey and Bernal, and in 1953 was submitted to rigid experimental control by Stanley L. Miller in the Chemical Laboratory of the University of Chicago in U.S.A. Miller constructed a special apparatus in which for a longest period of time (one week) was produced an electric discharge in an atmosphere constituted precisely by aqueous vapours, methane, and ammonia. The water circulated continuously in changing states, from the liquid state in the boiling flask to the gaseous state in correspondence to the electrodes, and then again for condensation in the liquid state in the flask. It was observed from the first day that the water was light yellow in colour and then turned decidedly to dark red at the end of a week. It was evident that the colour depended on some organic compounds formed during the experiments. These compounds were submitted to a very precise chemical analysis and were identified as Amino acids.
Source of activation energy and reaction energy for the above Reactions. Two different sources of energy were undoubtedly available on the primitive earth. One of these was the powerful electric discharge in lightning which must have occurred almost continuously in the early cloud-laden atmosphere. Secondly, although light rays could not pass through water vapours forming dense clouds around the earth for a long time, high energy radiations of the sun, such as Ultraviolet rays, X-rays and others could however pass through them. The energy from these two sources could have either acted directly on the gas molecules of the atmosphere and the resulting compounds could then have been washed down by rains into the seas. Or the reactions could have taken place in the waters of the oceans where methane and all other necessary ingredients were present in solution.
The early organic compounds described above, subsequently made possible the synthesis of macromolecules with unique chemical properties.
LATER ORGANIC COMPOUNDS
Presumably five major and several minor groups of new molecules emerged from the interactions of early organic compounds. Later, these came to have particular significance in the origin of life. The five major groups were:(l) Adenosine Phosphates (2) Polysaccharides (3) Fats (4)Proteins (5)and Nucleic acids.
Adenosine-Phosphates. These belong to a highly important class of compounds known as Nucleosides. A nucleoside molecule is a combination of a simple sugar and nitrogen base. For example:
Ribose (Pentose sugar) + Adenine (Pyrimidine)= Adenosine (Nucleoside)
Various kinds of sugars and Nitrogen bases in the early seas must have combined to form various nucleosides, including Adenosine. Plenty of phosphates could also be available in sea water which when combined with adenosine formed
Adenosine + 1 Phosphate = Adenosine Monophosphate(AMP)
Nucleotides- Nucleotides ( Adenosine + 2 Phosphates = Adenosine Diphosphate (ADP)
Adenosine + 3 Phosphates = Adenosine Triphosphate (ATP)
Biologically occurring derivatives of phosphorus play a Key role in the energy transactions of living organisms. ATP is a ‘high energy compound’. The expression ‘high energy compound’ or ‘high energy bond’, as used in biochemistry, has a meaning quite different from the physio-chemical significance of high energy bond. As noted early, in physical chemistry a ‘high energy bond’ is one which requires large amount of thermochemical energy for dissociation. In biochemistry, on the other hand, the expression ‘high energy bond’ refers to the large free energy emissions associated with definite reactions of that bond such as hydrolysis or group transfer.
ATP (Adenosine triphosphate) has got one phosphate group more than ADP (Adenosine diphosphate). The addition of this third phosphate group to ADP requires a great deal of energy which may be provided by various energy yielding reactions, particularly decomposition reactions of organic material like sugars and fatty acids. The ATP so produced is a rich source of energy. If the bond between the second and third phosphate groups is broken, the energy released becomes available for the support of other chemical reactions. ATP thus serves as an intermediate product, it traps energy from one source and makes it available for a different reaction. This has got a great significance in the living matter today. For example the carbohydrates in the animal tissue cells, such as muscle cells, are utilised as a direct source of energy which is liberated when glycogen or glucose is broken down through a long series of phosphorylated intermediates and finally oxidised to carbon dioxide and water. Possibly, ATP has been the basic unit of energy transfer throughout the ages even before living matter existed. Solar energy continued to supply energy for reactions but AdenOsine phosphates provided an alternative to it as a readily usable chemical energy source which could produce reactions independent of solar energy. This phenomenon had an important role in the origin of life because reactions involving the synthesis of complex organic compounds in living bodies cannot avail energy from physical sources directly. They require chemical energy and this is supplied mainly by ATP.
Polysaccharides. These are combinations of a few or many monosaccharide molecules. Polysaccharides may be composed of a single kind of monosaccharides (simple sugars), as in the case of Glycogen which contains several thousands glucose units; or Cellulose in which 2000 units are contained: or they may be composed of two or more kinds of monosaccharides.
The chemical process in which molecular units of similar or identical types are synthesized into a single larger molecule is known as Polymerisation.
Properties of Polysaccharides. (1) Building materials. (2) Energy source.
Fats. These are combinations of glycerine and fatty acids.
1 Glycerine molecule + 3 Fatty acid molecules = 1 FAT molecule.
Properties of Fats. (1) Building material. (2) Energy source.
There are many varieties of Fats depending on the types of fatty acids taking part in their synthesis. Living matter could not have come into existence with fats, polysaccharides and ATP alone in the early seas. Its origin became possible as the result of formation of protein and nucleic acid macromolecules.
Proteins. These are polymers of amino-acids. Some two dozen different types of amino-acids exist and any or all of these may be present in a protein in any number and any sequence. In many proteins as many as 100,000 or more amino-acids may be present. At the cellular and subcellular levels proteins provided building block units of far grater diversity as compared to polysaccharides, fats, water and other inorganic materials. Just as a chain of several hundred links can be looped and twisted into innumerable three dimensional shapes, so may a chain of protein be looped, coiled and twisted into a very large number of molecular shapes. It was due to proteins that a most complex and well finished structure as that of a living organism became possible.
The structure of proteins enabled them to function as enzymes and thus increased the speed of biological reactions tremendously. Reactions which could have taken centuries before the origin of proteins, could now occur within minutes and seconds. Proteins not only enhanced the speed of reactions but they also controlled the types of reactions that could occur in living matter.
Nucleic acids. In the early phase of the molecular evolution only simple molecules were formed. Later, more complex molecules such as amino-acids and proteins came into existence. In the more advanced phases of this period, it is believed that there appeared a molecule with two entirely new properties-(l) The ability systematically to direct the formation of copies of itself from an array of simpler building blocks. (2) And the property of acquiring new chemical configurations without loss of ability to reproduce. These properties, self-duplication and mutation, are characteristics of all living systems and they may therefore be said to provide an objective basis for defining the living state. This molecule was Nucleic acid.
Nucleic acids are high polymers of nucleotides. (Nitrogen Base + Simple Sugar + Phosphates) n = Nucleic Acid, where ‘n’ indicates large number. Nucleic acid molecules are as large or even larger than the most complex proteins. There are innumerable structural varieties of Nucleic adds. Any number and any sequence of nucleotides may be present in its molecule.
We may explain further the properties of nucleic add described above:-(l) Nucleic acids are carriers of biological information in a structural code. The following shall illustrate-when a person speaks P-A-K-I-S-T-A-N, it gives us the information that he says Pakistan. But the above letters together make the word Pakistan only when they are spoken in the above sequence. Similarly the sequence of nudeotides in a given nucleic acid carries information or a set of instructions how to build proteins. The nucleotides sequence determines what kinds of amino-acids will make up a protein and in what order they will be linked together. Thus the specific configurations of differently structured proteins depend on the specific arrangement of the nucleotides in a nucleic acid molecule. (Fig. 16) shows information code and protein synthesis. If ‘1-2-3-4-5 represents a portion of a nucleic chain, the structural characteristics of the nucleotide segment 1-2 could be such that only amino acid ‘a’ could attach there. Similarly only amino acid ‘b’ might be able to attach to the nucleotide segment 2-3 and amino acid ‘c’ to the segment 3-4 etc. If then the amino acids become linked together and form a protein, the sequence of amino acids will have been determined by the coded information contained within the nucleic acid chain.
Thus in all living organisms today, proteins are synthesized according to building instructions contained in nucleic acids. This is of great importance because proteins provide the building blocks and
Fig. 16-Nucleic acid provides information code for building protein molecules.
also function as enzymes which control all reactions in living matter. In short all the life processes are ultimately controlled by Nucleic acids.
(2) Auto-reproduction-Depending on the above information carrying property is the unique property of Auto reproduction or duplication. The molecules of nucleic acids are able to synthesize new molecules perfectly identical to the model. The process is similar to the control of protein-synthesis by nucleic acid. In the building of proteins, the raw material was amino acids and here the raw material is nucleotides. Thus a nucleic acid molecule is able to reproduce itself without the aid of any other controlling agency. (Fig. 17) indicates the process of nucleic add reproduction, (A) A preexisting nucleic acid molecule (Shaded) surrounded by raw materials (i.e., nudeotides) needed for the construction of a nucleic acid duplicate.
- B) A nucleotide of a given type has affinity for a corresponding. component of a nucleic acid. The respective nucleotides therefore get attached in matching sequence to the pre-existing nucleic acid. (C) The nucleotides having taken up their positions link up with Another. (D) The new nucleic acid. molecule so created separates from the original model. Model and replicas are identical in composition.
The first nucleic acid probably came into existence through random polymerization of random nucleotides. But once the first nucleic acid appeared, it multiplied by the process of duplication. Thus reproductivity which is a peculiar characteristic of living beings, actually started at the molecular level, before the origin of first living units. The information code for the synthesis of particular proteins passed on from one generation of nucleic acid to the other, so that each generation could recreate the protein types of its ancestors.
(3) Mutation-Related to the property of Auto-reproduction is another unique property of nucleic acid which later became the characteristic of life. It is the property of acquiring new configuration without loss of ability to reproduce. Molecules of nucleic acids are most stable. They are not easily affected by the physical and chemical forces operating on the earth, as most compounds do. But occasionally certain chemical and physical agents such as ultraviolet rays succeed in producing minor changes in their structures. These changes may be (a) the alteration in structure of one of the component nucleotides, (Fig.l8a); (b) Or a short sequence of
nucleotide chain may be detached from the rest of the chain at one particulate place and reunite at a different place; or in an inverted position; or
Fig. 18a. -NUCLEIC ACID. MUTAION
the sequence may be correct, but during reproduction a wrong type of nucleotide gets attached at an otherwise correct position. (Fig. 18b).
Whereas metabolic errors or deviations in other compounds are constantly erased or repaired by the turnover process, the errors in nucleic acid synthesis become permanent. The altered nucleic acid becomes stable and later reproduces the changed condition which is transmitted from one generation to the other. Such stable alterations are called Mutations.
Fig. 186.-OTHER ERRORS IN MUTATION.
Thus nucleic acids on the early earth not only reproduced their own kind but some of the descendent molecules became different from their ancestors. These differences accumulated through successive generations, so that entirely different and varied types came into existence.
As the nucleic acid molecules changed with the passage of time, the protein molecules whose synthesis depended on nucleic acid, changed accordingly, giving rise to new and diverse types of proteins. And proteins being the building blocks, diverse types of organisms came into being.
Thus the chemistry of the earth took entirely a new turn with the origin of nucleic acids. They carried genetic information from one generation of molecules to the other and controlled the protein synthesis accordingly. Moreover nucleic acid maintained its stability despite acquiring new chemical configurations. Some of the chemical processes on the earth thus ceased to occur at random and became strictly controlled both as regards their permanence as well as change.
A summary of Later Organic Compounds is given below in (Fig. 19)
- Adenosine Phosphates
- Nucleic acids.
(1) Adenosine phosphates (Nuclcotides).
Ribose (Pentose sugar) + Adenine (Purine)= Adenosine (Nucleosidcs).
Adenosine + 1 Phosphate = Adenosine Monophosphate(AMP) Nucleotides
Adenosine + 2 Phosphates = Adenosine Diphosphate(ADP)
Adenosine + 3 Phosphates = Adenosine Triphosphate(ATP)
Properties-1. Energy Trappers and Energy Donors.
Source of Energy-Decomposition of sugars and fats.
(2) Fats-1 Glycerine molecule+3 fatty acid molecules = 1 fat molecule.
Properties-(1) Building materials. (2) Energy source.
There are many varieties depending on types of fatty acids.
(3) Polysaccharides-Polymers of sugar molecules. Energy source-ATP.
Example-Glycogen contains several thousand molecules of simple sugar. Properties-d) Building materials. (2) Energy source.
(4) Proteins-Polymers of amino acids.
100,000 or more amino acids may be present in a protein molecule. Some two dozen types of amino acids arc known. Any number, any type and any sequence may be present in a protein molecule. .Properties-(1) Building materials. (2) Enzymes.
(5) Nucleic Acids-Polymers of nucleotides. Some molecules are as large or even larger than protein.
Properties-W Information code. (2) Reproduction. (3) Mutation.
Fig. 19.-LATER ORGANIC COMPOUNDS (SUMMARY)
The events described so far constitute molecular evolution. To describe briefly seven types of chemicals originated gradually in due course of time and accumulated in the early oceans:-
Inorganic Substances-(1) Water (2) Minerals.
Organic Substances-(1) Adenosine phosphates (2) Carbohydrates (3) Fats (4) Proteins and (5) Nucleic acids.
The subsequent events may be described as Prebiological stage of chemical evolution i.e., the actual formation of first living units or cells from the above. compounds.
PREBIOLOGICAL PHASE OF CHEMICAL EVOLUTION.
(Birth pangs of life on the earth)
Cells are the basic living units. They are microscopic watery drops which contain many types of organic and inorganic compounds. With the origin of cells the chemical evolution still continued, molecules still continued to produce new molecules, but out of the organic molecules emerged entirely a different creation, with the properties of life. This happened to be a most important landmark in the evolutionary history of the earth.
It is estimated that the first cells appeared 200 million years ago. The details of origin of first cells is not clear. The following is a general outline of the sequence of events which led to cell formation, consistent with the laws of physics and chemistry known today.
Origin of Cells. The first cells may have been produced in the following ways:-
Somehow or other the organic compounds described above assembled into small cohesive drops and by virtue of the properties of the aggregated material, life began to appear in these drops. The first question arises as to how could the aggregation of these organic compounds occur. The sea water in which they were present was too dilute a medium in which they could keep proper concentrations. Moreover it was difficult for all the necessary ingredients to assemble all at a time and stay in that condition for a sufficiently long period, because after chance contact the mighty waves of the sea were sufficient to disperse them again. Therefore it is much more likely that the assemblage of various molecules occurred at the sea shore, where they could stick to appropriate surfaces on solid ground.
ADSORPTION or PROPERTY OF STICKINESS is a surface phenomenon in physical chemistry and molecules of sugars, fats and proteins get adsorbed to various surfaces. Nucleic acid molecules are also very much adsorbable. On the other hand, fine particles of sand and clay are excellent adsorbing materials and plenty of them must have been present along the sea shore. Most probably some of the molecules got adsorbed into clay at random, at different places. More molecules of the same or different types might have been added later. Thus there was ample chance for all the key molecules to assemble inside the tiny little spaces in clay where they could form adequate concentrations to react with each other. The reactions could have been accelerated in the tidal zones, by evaporation of water.
It is not necessary that all the complex organic compounds such as polysaccharides, fats, proteins and nucleic acids were first formed in the ocean water and then. aggregated into clay. Rather it is more likely that simple organic compounds such as sugars, fatty acids, amino-acids and nucleotides got adsorbed into day where the macromolecules of proteins and nucleic acids etc. got synthesized, because their synthesis required the close proximity of the necessary ingredients and the energy sources.
It has been experimentally demonstrated that if concentrated mixtures of amino acids are heated under NEAR DRY CONDITIONS, protein like compounds are formed. Similarly mixtures of other appropriate starting compounds heated under almost dry conditions can yield products having some of the characteristics of nucleic acids. The tiny pockets in clay therefore provided favourable environments for the concentration and mutual reactions between raw material molecules. Once the nucleic acids were formed, they must have been followed by protein synthesis and some of the proteins enzymes led to the formation of Polysaccharides and tats etc.
Mixtures containing fats and proteins have got the property of forming surface films. It is a common experience that if a cup of boiled milk or a plate of hot custard are allowed to cool, a thin film forms at the surface. Certain proteins have also got the property of forming precipitates out of solution which turn into granules or (threadlike structures). For example, during bleeding, fibrinogen in the blood plasma gets converted into fibrin (a threadlike structure) and a clot is formed. Polysaccharides, like cellulose (in plants), also can make films or fibrils. Thus some of the organic compounds in the tiny pockets in clay must have constructed external boundary membranes and internal network of fibrils in which the members of the assembly, i.e., water, minerals, ATP, Polysaccharides, fats, proteins and nucleic acids got enclosed. The individual units so formed came to be known as cells. Being protected by external membranes they could remain as separate individuals, even if they were washed into the sea later.
The first cells on earth must have come into existence in various parts of the world and their origin must have been preceded by numerous trials and errors. For a long time the right type of raw material molecules could not have aggregated together; or even after aggregation they may not have been in correct proportion; or if they fulfilled all the requirements for reactions to occur and proceed in the right direction, they could have been washed into the sea before the synthesis of end products could be completed. On the other hand the mixtures of raw materials, instead of remaining in the state of near dryness for an adequate period, could have dried up completely; or if all went well, up to the stage of cell formation, the cells themselves might have dried up and destroyed inside their places of birth by the heat of the sun. Yet after so many false starts and incomplete endings which continued for millions of years, some of the cells could leave the clay, to safely enter the sea water. With the conditions prevailing on the earth and the kind of materials that had accumulated in the early oceans, the origin of first cells was not a matter of chance but a matter of time.
It is not necessary that the above description corresponds in details to the actual events that took place in the remote past but such processes that could result in cell formation are plausible within the scientific domain of physics and chemistry.
The above description regarding the origin of life is based on the research work, by the world scientists during the last several decades. The evolutionary history beginning with unicellular organisms up to the appearance of Man shall be described later, but we must state at this juncture what the Holy Quran said fourteen hundred years ago, about this phase of chemical evolution passing on to biological and ultimately leading to the emergence of Man.
Let us point out at the outset that the Holy Quran is self explanatory and clarifies itself by presenting a subject in various ways and in different contexts, so as to make things easily understandable. Thus it is said:
“We have explained to mankind by displaying different aspects of things in this Quran, with every kind of similitude.”
It has been explained already in this chapter, the phase of chemical evolution leading to the emergence of life cells which form the initial stage of Biological evolution and which ultimately led to the appearance of man on the stage of life: As we have noticed life originated from the inorganic materials of the earth. The Quran says
“It is He who created you from dust (inorganic matter)”.
The role of the first compounds in the origin of life, of which water has been the most important single component have been explained. Water as said earlier, took the role of key which opened the door to life. The Quran says:
“And it is He who has created man from water”.
It means that the presence of two essential elements water and inorganic material of which the carbon was most important, took the basic role in the emergence of life. The Quran says:
“It is He who created you from clay”, i.e. the combination of water and other inorganic materials.
A wrong notion is prevalent that the Creator first prepared the mould of man out of clay, gave it life and named him Adam. Then He bisected the side of his body and got out of it his a female companion. From then onwards started the progeny of man. This is in fact a Biblical story which our commentators have monkeyishly copied, due to their ignorance of the scientific facts of chemical evolution followed by biological evolution, each one of which lasted for millions of years.
According to the Holy Quran, life came into existence not from a lumpsum of day but from the extracts of clay which gradually reached the stage of man. The Quran says:
“And We created man from the extracts of day”.
What is this extract of day? It is the compounds of carbon which eventually evolved in to the later organic compounds such as Adenosine phosphates, polysacharides, fats, proteins and Nucleic Acids in the company of minerals.
As stated earlier, the organic material in the sea water stuck to the clay present on sea shores and formed a preliminary step in the creation of life. This combination however could not occur without the property of adsorption present in the molecules of organic compounds. The clay on the sea-shore was the excellent adsorbing material; the same property being also present in the fats and proteins etc. The Quran says:
“Verily We created them out of sticky clay”.
As stated earlier, concentrated mixtures of Amino Acids when heated to near dryness, protein like compounds are formed. Similarity mixtures of other appropriate starting compounds, when heated under almost dry condition, can yield products having some of the characteristics of Nucleic Acids. This condition of near dryness could occur at such sea shores which were not affected by frequent tidal waves, for quite some time.
The Quran says:
“And verily We created man from old physically altered mud which after a lapse of time reached the stage of near dryness”.
“Most of the commentators have wrongly interpreted the word in verse (15:26) above as ‘putrified mud’. It is an established fact that decay was unknown on the earth before the orgin of bacteria which are living objects. The word actually means “old mud which with the passage of time had undergone physical and chemical changes; not putrifaction which is a biological phenomenon”.
“He created man from mud nearly as dry as pottery (the stage of near dryness).
Thus in the verses described above the Quran provided significant pointers to the origin of life, in its own particular way: from earth (or inorganic matter); from water; from clay (or wet earth); from sticky adsorbent clay; not clay as a whole but from extracts of clay i.e., its active principles which were the precursors of the units of life; from old mud subjected to physical and chemical changes; from mud which reached the stage of near dryness
The above was proclaimed in the 7th century A.D., by one who did not know how to read and write before revelation came to him. How beautifully the story of the creation of life was disclosed, at a time when human knowledge was extremely rudimentary. Even in the present age of advancement, how many people are there, other than the scientists, who know these facts?
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