Tag Archives: Life Appears on the Earth
“How do you disbelieve in Allah (when you see that) you were without life and He gave you life”?
BASIC PROPERTIES OF LIFE
The cells that exist today are composed of the same seven types of chemicals which constituted the first cells on the earth billions of years ago; i.e., water, minerals, Adenosine – phosphates, polysaccharides, fats, proteins and nucleic adds. The early cells drew inorganic as well as simple organic matter directly from sea water for their nourishment. This was a simple form of Nutrition. The raw materials thus used are called nutrients. The term food is used for complex organic nutrients.
As already noted, the decomposition reactions of organic materials such as fats and carbohydrates yielded energy which was captured by Adenosine-phosphates. These especially ATP served as a readily available source of energy for the chemical reactions within the cells. This process of trapping energy from one source, and transferring and packing it up in a different substance, we call Respiration. What is the significance of Respiration? The bonds between the Hydrogen, Oxygen and Carbon atoms of Carbohydrates and fats are low energy bonds, but for the complicated cellular reactions to take place very high energy source is required. This high energy source becomes available in ATP. Fuel molecules are smaller in number but high in energy contents. Thus ATP provides a readily available source of high energy within cells. We may call respiration a power generator which maintains life. Carbon dioxide is one of the products of respiration. As the respiring cells increased in number, the quantity of carbon dioxide consequently increased. Some of it dissolved in the sea water and the rest escaped into the atmosphere where it accumulated and formed a screen for high energy solar radiation, a portion of which could not reach the earth any longer.
With the availability of nutrients and ATP, a cell could duplicate nucleic acids. With increase in the number of nucleic acids more proteins could be manufactured. Proteins being enzymes could manufacture more fats and polysaccharides. Thus a cell could maintain itself by replacing the worn-out or damaged parts. This we call Self repair.
As the synthesized compounds got accumulated within cell, it became larger in size. Thus synthesis led to its Growth.
New types of compounds came into existence giving the cells new properties. This resulted in molecular Development.
As described before, nucleic acids became the ultimate controllers of cellular reactions. The cellular nucleic acids came to be known as Genes. Being gene-controlled cells became stable, so that the activities of cells such as nutrition, respiration, synthesis and growth could continue as before. That is why the cells still exist today and exhibit the same basic characteristics as the early cells.
The growth of a cell on account of synthesis and internal molecular reproduction could take place up to a certain limit, after which the cell became unstable. Thus the cell reproduced itself. By reproduction the cells not only became multiple but their generations continued in succession. Thus all cells that exist today are successors of the first cells on the earth. As the first cells increased in number, the nutrients in the sea water decreased. The cells had to compete for the supply of nutrients. Thus only those cells could continue their existence, which Adapted themselves to the new environments, i.e., either they could utilise the existing food more efficiently or more rapidly, or could find new methods of producing or procuring food.
Any change in the properties of cells could take place only if the genes had changed. This could occur by the occasional fusion of two cells. The fusion could be either partial or temporary, with resultant exchange of certain genes; or could be total and permanent, so that the genes of both cells became pooled together. With the change in genes the new cell properties became stable. This process of pooling or exchanging genes amongst two different cells came to be known as Sex. Genes could also change through Mutation which provided cells better chances of survival than sex. After mutation more cells and their offspring could get food in spite of competition.
The fusion of cells and gene change have always been at random. Any two cells may fuse by chance and any genes may get exchanged after fusion. This had two types of results. The new cells produced by pooling or exchange of genes had their competitive capacity increased or decreased according to the type of environments in which they were placed. The cells that adapted the new environments persisted in the succeeding generations. On the other hand, poorly adapted cells became extinct. Such changes, with the appearance of new types of cells with new characteristics, through successive generations, constituted Evolution.
Thus we may summarise that a living cell has got the following basic characteristics:-
(1) Nutrition (2) Respiration (3) Self repair or the maintenance of internal steady state (4) Synthesis resulting into growth and development (5) Reproduction and (6) Adaptation through sex and mutation. Collectively we may term these properties as life.
Nucleic acid probably lay freely suspended inside the first cells in the form of clumps as we can notice in the primitive cells today. It must have happened that after accidental rupture or after death of cells these clumps escaped into the sea water where they remained inactive. But if they happened to enter another cell, they again became active and began duplicating themselves by using the living apparatus of that cell. These clumps of gene forming nucleic acid may have been the ancestors of viruses because this is how the viruses behave today. For example in the case of smallpox virus, it becomes active when it enters the cells of human body, and it begins to duplicate and produce specific types of protein. As the new types of protein are not tolerated by the human cells, reaction occurs in the form of disease.
EARLY CELL TYPES
Two types of cells are important from the point of view of early evolution. As noted above, first cells had nucleic acids freely suspended in their interior. The nucleic acids together with certain proteins formed nucleoproteins. In some of the descendants of early cells loose clumps of nucleoproteins concentrated towards the centre, but lay scattered inside the cells in direct contact with the endoplasm. This type of cell came to be known as Monera. Bacteria and Blue-green Algae are the modern representative of Monera group.
Bacteria are literally found everywhere, floating with dust particles in the air, in salt and fresh waters, in the water of hot springs, frozen in ice, in the upper layers of soil and in the bodies of plants and animals. They are often called germs or microbes because they live on or within the human body as parasites and bring about disturbances chiefly chemical which we term disease. Besides these parasitic forms which are few in number, human life and life in general on the earth, as we shall see in later chapters, could not continue long without the services of bacteria. Their size varies from 1/1000 inch to 1/50,000 inch.
In another major type that descended the first cells, the gene containing nucleoproteins concentrated in the centre of each cell, forming a loose mass. A thin membrane formed round the mass, and the nucleoproteins no more remained in direct contact with the rest of the cell substance. This type of cells came to be known as Protista. The loose central mass of cell later evolved into compact nucleus. All the modern plants and animals have descended from protista.
NUTRITIONAL EVOLUTION ( )
There had been a tremendous expansion of living mass from the first cells on earth. It makes an interesting study from Quranic point of view how with the gradual disappearance of the free molecular food from the oceans, the nutrition of a vast number of organisms that branched out from the first cells, could be maintained. This happened in the following ways:-
(1) Parasitism. With the disappearance of free molecular food from the oceans certain organisms began to procure food from the bodies of living organisms. We noted above, how viruses entered living cells and became reactivated. Similarly a cell could invade another cell for obtaining food. This type of procuring food is called Parasitism. Even today viruses and bacteria get their food by Parasitism.
(2) Saprotrophism. Here the organisms began to live on dead bodies of other organisms. Many types of bacteria adopted this method of obtaining food. Decay in the dead bodies of organisms results from the invasion of nutrients-gathering saprotrophic bacteria.
The decay was unknown on the earth before saprotrophism, but these bacteria are so abundant today that anything exposed to air or water immediately begins to decay.
(3) Holotrophism. It is the process of eating whole living cell. In parasitism the smaller cell eats the substance of the larger cell, while in holotrophism the larger cell engulfs and eats the smaller cell.
It is evident from the above description that the above three methods of food gathering did not add anything to the total food stores on the earth. It was just one cell eating the other dead or alive. Thus unless some new food sources had become available, the life would have gradually ceased to exist on the earth. Such food sources did evolve and the cells themselves started manufacturing food within themselves. In early stages we noted that nutrients were produced by methane, ammonia and water, and energy was supplied by the sun and lightning in the clouds surrounding the earth. This method of food production became inadequate at a later stage, as with the disappearance of permanent clouds, lightning became rare; and with the formation of carbon dioxide screen in the earth’s atmosphere, high energy solar radiation became unavailable. Thus the evolution of some new methods of manufacturing organic compounds became necessary. Water was still abundantly available and in addition to methane and hydrogen cyanide, carbon dioxide was available directly within cells as a source of carbon, this being the product of respiration. With water and carbon dioxide, cells could produce organic compounds, provided a source of energy were available. ATP could supply such an energy but this itself was an organic compound and its production depended on an external source of energy. Thus cells could continue to exist only if they evolved methods of utilising external sources of energy. This happened in two different ways:-
Chemosynthesis. Early Monera and Protista, especially certain types of bacteria, started extracting energy from sulphur, iron and nitrogen compounds. They absorbed these compounds into their bodies and on account of certain reactions that took place bonds were broken, and bond energy became available for the synthesis of carbohydrates from carbon dioxide and water. This process is called chemosynthesis and is still availed by certain bacteria. But the process had its limits, as it depended on the availability of certain chemicals.
Photosynthesis. Another method in which materials and energy could be available in abundance came into existence. A huge source of energy was present in the light rays of the sun, only an energy-trapping substance was required within the cell. Such substance came to be evolved in the form of Chlorophyll. The process of manufacturing organic compounds, by means of chlorophyll and light rays, came to be known as photosynthesis and is still used by the plant cells all over the world. It saved the living organisms from premature extinction.
We note that out of the five food procuring methods that came into existence sooner or later, i.e., Parasitism, Saprotrophism, Holotrophism, Chemosynthesis and Photosynthesis, only the last two added to the total food supply on the earth. It appears that Monera adapted all methods of getting food except eating. Protista adapted photosynthesis as well as holotrophism (eating). Two different types of organisms evolved from the protista. One group became specialised in photosynthesis and all the plants on earth evolved from this group. The other group specialised in holotrophism (eating) and became animals.
The above description of nutritional evolution illustrates a beautiful link in the chain of Allah’s ‘RABUBIYYAT’ which is one of the attributes or basic characteristics of God and means the provision of sustenance to an object from its initial stage to the stage of final destination. The Holy Quran begins with the verse ( )
“Praise be to Allah, the Cherisher and Sustainer of the universe”.
FREE OXYGEN MOLECULES REAPPEAR ON THE EARTH
As sated earlier, with the formation of first compounds, free molecules of oxygen, hydrogen, nitrogen and carbon disappeared from the earth. With the appearance of photo-synthesis free molecular oxygen reappeared and continued gathering in the atmosphere. The photosynthesis reaction is as follows:-
Carbon dioxide + water = Carbohydrates + oxygen.
This brought about a slow oxygen revolution on the earth. Oxygen has the property of reacting readily with other substances. Thus it reacted with methane to produce carbon dioxide and water:-
CH4 +202= C02 + 2H2o
It reacted with ammonia to produce water and nitrogen molecules:-
4NH3 +302= 2N2 + 6H2O
It reacted with Hydrogen cyanide to produce carbon dioxide, water and nitrogen molecules:-
4HCN +502= 2N2 + 2H20 + 4C02
Thus the ancient atmosphere containing methane, ammonia and hydrogen cyandie transformed into a modern one, containing water vapour, carbon dioxide, nitrogen molecules and oxygen molecules. At high altitudes, under the influence of high energy radiation from space, oxygen molecules reacted with one another to produce Ozone. As noted earlier, several miles above the surface of the earth, Ozone forms a screen against the high energy radiation and this is one of the guards ( ) that protect life on the earth. Modern animals and plants are not adapted to high energy radiation and are killed by exposure to it. But the Monera and Protista which evolved before the formation of Ozone layer were adapted to high energy radiation and are still radiation resistant.
Free oxygen also reacted with the solid crust of the earth and converted pure metals and minerals into oxides which form the ores and rocks of the modern land. Moreover with free oxygen available in abundance a much more efficient form of respiration came into existence. The earliest cells had anaerobic (without air) form of respiration known as fermentation. It consisted of decomposition of food molecules without oxygen, which liberated energy that could be used in the formation of ATP. Free oxygen, on the other hand, could provide more energy, per food unit consumed, than in fermentation. Thus with free oxygen available, aerobic (with air) form of respiration came into existence.
Fig. 22.–EFFECTS OF REAPPEARANCE OF FREE OXYGEN MOLECULES ON THE EARTH.
Fig. 23.–SUMMARY OF EARTH’S EARLY EVOLUTIONARY HISTORY.
(In relation to the appearance of life)
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