MODERN HYPOTHESIS OR CHEMICAL THEORY OF ORIGIN OF LIFE (OPARIN-HALDANE
THEORY)
The modern hypothesis of origin of life was formulated by Haeckel. His idea was elaborated in the chemical theory by two workers independently: a Russian biochemist A.I. Oparin in 1924 and an English biologist JIt was summarized by Oparin in his book "The Origin of Life" published as an English edition in 1938. This theory (also termed iogenesis theory) states that life originated from inanimate matter by a series of chemical reactions on the primitive arth as summarized by Oparin in his book 'Origin of Life' as 'abiogenesis first, biogenesis ever since'. This theory is now known as primary abiogenesis. c requirements for the (02)], right chemicals (including water, various inorganic ions and organic molecules); an energy source, and infinite time Earth's surface and atmosphere during the first billion years of it existence wereradically different from today's conditions. Primitive atmosphere on earth was reducing. In primitive reducing atmosphere various new chemicals were formed and aggregated. First life arose from such aggregation and formation of chemicals through a progressive series of chemical reactions. Thus, life originated on earth in steps, not as an instant product. Scientists believe that life originated in water, not on land because deep sea water protected life from harmful effects of intense UV radiations from Sun. With evolution of photoautotrophs (aerobic) oxygen was liberated in atmosphere. Eventually ozone molecules formed by reaction of oxygen molecules and they formed a thick layer in atmosphere ie., ozone layer. This layer blocked entry of UV rays. After that life migrated from water to land.
STEPS IN THE ORIGIN OF LIFE
Scientists separate the entire process of origin of life into the following steps: (i) origin of earth and its primitive atmosphere: (i) chemical evolution (chemogeny); (ii) biological evolu
Origin of Earth and its primitive atmosphere earth was a fier ot gases
and vapours of various elements. Gradually, through hundreds of o a molten core and different elements got stratifiet ones like helium, hydrogen, oxygen, niTrogen and carbon etc., flowed to the surface and fo rmed the gaseous atmosph which ought to have been different from f the atmospheric gases liqu hot. As the earth gradually cooled further nto water and resulted in rain
efied, and some of the liquids turned into solids. Steam condenseTh the atmosphere of primitive earthapo layer was present in the atmosphere so UV rays from s
These UV rays, electric arges from thunder clouds, heat om volcanic
eruptions, cosmic rays etc., provided energy for arious chemical reactions.
Chemical origin of life (Chemogeny)
rth, elements like H, 0, C, N could not bond together. With gradual cooling of earth ources produced more and more com acids, amino acids etc. mperature of ear and formed simpl to ides, ammonia, methane cyani nplex organic compounds. de etc. Thesese free atoms came toge compounds under the influe First organic compounds were hydrocarbons. Further reactions resulted in formati ester on of m complex compounds, such as s and other complex organic substanc probably occurred in sea, which had been substances came together arbohydrates, fats and amino acid escribed by Haldane as The hot dilute soup'. In the hot organic soup the moleculesin increasing number, collided, reacted and aggregated forming new molec rgalycerol united to form fats, sugars, nitrogenousbases and phosphates combined into nucleotides which polymerized into nucleic acids. Amino acid units joined to form polypeptidesand proteins. Water and ammonia were probably the first compound molecules of primitive earth. First organic compound wasSimple sugar units combined to form large sugar or starch molecules. Fatty acids and gethane. Later on hydrogen cyanide was formed. Formation of protein molecule is considered a landmark in the origin of life.24) observed that if a mixture of a large protein and a polysaccharide is shaken, coacervates are formed. The coacervatesome water. Oparin's coacervates also show a simple form of metabolism. As thesecontain mainly proteins, polysaccharides and scoacervates do not have lipid outer membranes hence they cannot reproduce.B.S. Haldane in 1928.
