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Origin Of Life


The origin of life is the process by which living organisms develop from inanimate matter which is generally thought to have occurred on earth between 3500 and 4000 million years ago.

There are several theories about the origin of life. These are theory of special creations, theory of eternity, theory of catastrophism, cosmozoic theory, theory of spontaneous generation and Oparin Haldane theory.

  • Theory of special creation was proposed by Hebrew and his coworkers and supported by Father Saurez. According to this, life was created by supernatural power either once or at successive intervals.
  • The theory of eternity of life, also called the steady state theory, states that life has even been in existence as at present and will continue to be so forever, changing only in form. It neither had a beginning nor will have an end. According to this theory, scientists like Richter, Preyer, Helmholtz, Arrhenius, Hoyle and Bondi believed that life is immortal.
  • Sudden creation of life from inorganic material was supported by George Cuvier. This theory is called theory of castastrophism or cataclysm.
  • Cosmozoic theory was proposed by Richter and supported by Arrhenius. It is also called the theory of panspermia (or life spore). According to this theory, life had reached the earth from some other heavenly body in the form of resistant spores of simple organisms.
  • Theory of spontaneous generation or abiogenesis or autogenesis states that life originated from non-living things in a spontaneous manner. It was believed and supported by Thales, Anaximander, Newton, Descrates and Van Helmont.
  • The theory of spontaneous generation was disproved by Franceso Redi, Abbe Lazzaro Spallanzani and Louis Pasteur.
  • Francesco Redi performed a series of experiments to disprove the theory. He placed meat under clean muslin coverings and demonstrated that while flies laid eggs on muslin, maggots or larvae appeared only when those eggs were transferred to the meat and allowed to hatch. He concluded that maggots develop only from pre-existing flies and were not spontaneously generated by any other form of material.
  • Abbe Spallanzani prepared flasks of meat broth which were boiled for several hours and then sealed. The broth remained clear for months and when the seals were broken and the broth tested, it was shown to be free of microbes.
  • Louis Pasteur conducted swan-neck flask experiment to disprove the concept of spontaneous generation completely.
  • All three scientists (Redi, Spallanzani and Pasteur) developed the theory of biogenesis. According to this theory, life originated from pre-existing life.
  • The modern hypothesis of the origin of life was formulated by Haeckel. This idea was elaborated in the chemical theory by two workers independently: A.I. Oparin and J.B.S. Haldane.
  • The modern theory of origin of life was propounded by Oparin and is based upon chemical evolution.
  • The Oparin Haldane theory (also called protobiogenesis) was experimentally supported by Stanley Miller. Modern views regarding the origin of life include the origin of earth and its primitive atmosphere, chemical evolution and biological evolution.
  • Primitive atmosphere was reducing atmosphere because hydrogen atoms combined with all available oxygen atoms to form water and leaving no free oxygen, water and ammonia were probably the first compound molecules of the primitive earth.
  • Chemical evolution (also called chemogeny) involves the synthesis of simple organic molecules. Experimental evidence for the formation of simple organic compounds was given by Stanley Miller.
  • Synthesis of complex organic compounds from their simple constituent molecules was experimentally proved by Stanley Miller with the help of ‘simulation experiments’. The apparatus used is ‘spark discharge apparatus’.
  • Protenoids are protein-like substances formed by polymerisation of amino acids under inorganic conditions such as heating to over 140°C. The formation of protein molecules can be considered a landmark in the origin of life.
  • Colloidal aggregates were named microspheres by Sidney Fox and coacervates by Oparin. Microspheres or coacervates are particles composed of two or more organic molecules. They were made from relatively complex mixtures of polypeptides, nucleic acids and polysaccharides.
  • Biological evolution (or biogeny) involves the formation of prokaryotes to eukaryotes.

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