About 100 years ago F. Engels defined life as the “mode of motion of a albuminous substances”. Modern sciences succeeded in tracing the stages of the evolution of life from a barren, entirely inorganic earth through the formation of organic compounds, their polymerization to giant-chained molecules of proteins and nucleic acids, the formation of living cells and the whole process of Darwinian evolution to man.
Polymeric compounds are chemical substances composed of the same elements in the same proportion but with different molecular weights. They are liquid or gaseous substances with small molecules (C2H2 — acetylene, C6H6— benzine).
Scientists have found ways of joining the small molecules together into long chains thus forming a solid with various properties of polythene or other plastic.
A similar process of the formation of long-chain molecules from small ones goes on in living cells. Proteins and ammo-acids are the building bricks of the living matter. Living organisms produce proteins from the food they absorb.
There are several hundred proteins. They are made from about 20 simpler molecules called the amino-acids. The amino-acids are joined nose to tail as are the molecules in polythene. But the structure of the chains in proteins is much more complicated than in polythene. Each type of protein is made of a precise number of each kind of amino-acid. There is even precise order in which each simple molecule joins the chain. Chemists are unable to produce such polymers yet.
Still we are getting some insight into the structure of natural polymers. We are beginning to understand the structure of chromosomes — thread-like parts of the cell dictating the order in which the various smaller molecules join together to make the long-chain nucleic acids RNA and DNA. RNA and DNA carry the genetic code which plays a big role in the process of heredity. We can’t yet answer the question when life began. It must have started with the development of self-replicating polymers.
Scientists have produced a brown soup which may be the sort of substance life on Earth developed from. Methane gas and ammonia were mixed, the mixture was bombarded with an electric spark for 24 hours. In this way our primitive atmosphere with its thunder-storms was imitated. Hydrogen cyanide was produced and it turned into a black solid. Next, water was added to it, and the black solid became a brown scum. The scum contained proteins. It is thought that a scum-like substance once covered the Earth.
Experiments like this had been made before. But this was the first time that proteins were produced, till then amino-acids had been obtained in all the previous experiments.
Life must have come from simple, non-living forms millions of years ago. It must have started in the earth’s primitive oceans, whose consistency was like thin soup.
The big difficulty of synthesizing life lies in the fact that the primitive conditions could never be exactly reproduced. Darwin said, “If we could conceive in some warm little pond with all sort of ammonia, phosphoric salts, light, heat, electricity, etc. present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day, such matter would be instantly devoured or absorbed which would not have been the case before living creatures were formed.”
Whether life can be made in laboratories in the next ten years remains to be seen. But such experiments show how the road to life started and, perhaps, how life forms started to evolve on our planet.
Do you know how much you weigh? Do not think this question to be very simple even if you have weighed yourself quite recently. Have you any idea how your weight varies during a day, by the evening, in an hour or even in ten minutes?
The weight of a human body is constantly fluctuating. Apart from quite obvious causes such as meals, when our weight increases spasmodically, there are others that bring about constant, slow, quite unnoticeable variations. The first to detect them was Sanctorius over 300 years ago. He constructed huge scales and spent hours, observing how his own weight changed. The results of this experiment were so surprising that numerous visitors gathered in his laboratory to see the eminent scientist lose weight in their presence. The changes were appreciable: overnight Sanctorius lost as much as a kilogram.
One can lose weight for various reasons. Loss of carbon dioxide alone accounts for a reduction of 75 to 85 grams over a period of twenty-four hours. This is only a trifle compared with the loss of water via the lungs which amounts to 150 to 500 grams in twenty-four hours, the quantity lost by perspiration being still greater. A man is constantly perspiring, although sweat does not run from his body in large drops.
From the openings in the numerous sweat glands scattered over the surface of the skin minute drops of sweat are exuded which can be seen only through a microscope. If the air is dry, they evaporate before new ones are discharged from the glandules, and the skin remains dry. In cold weather between 250 and 1700 grams of water are evaporated through the skin. A man doing hard physical work in dry hot weather exudes as much as 10-15 litres of sweat over a period of twenty-four hours, and sometimes as much as four litres, an hour. Even in this case, however, the skin may also remain dry. According to moderate estimations, people living in the southern regions secrete between 70 and 150 tons of sweat in the course of a seventy-year lifetime. This is enough to fill three large railway tank wagons.