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EVOLUTION old – almost 13.8 billion years old. Huge clusters of galaxies comprise the universe. Galaxies contain stars and clouds of gas and dust. Considering thesizeofuniverse,earthisindeedaspeck. TheBig Bangtheoryattempts to explain to us the origin of universe. It talks of a singular huge explosion unimaginable in physical terms. The universe expanded and hence, the temperature came down. Hydrogen and Helium formed sometime later. The gases condensed under gravitation and formed the galaxies of the present day universe. In the solar system of the milky way galaxy, earth was supposed to have been formed about 4.5 billion years back. There wasnoatmosphereonearlyearth.Watervapour,methane,carbondioxide andammoniareleasedfrommoltenmasscoveredthesurface.TheUVrays from the sun brokeup water into Hydrogen and Oxygen and the lighter H 2 escaped. Oxygen combined with ammonia and methane to form water, CO and others. The ozone layer was formed. As it cooled, the water vapor 2 fell as rain, to fill all the depressions and form oceans. Life appeared 500 millionyearsaftertheformationofearth,i.e.,almostfourbillionyearsback. Did life come from outerspace? Some scientists believe that it came from outside. Early Greek thinkers thought units of life called spores were transferred to different planets including earth. ‘Panspermia’ is still a favourite idea for some astronomers. For a long time it was also believed that life came out of decaying and rotting matter like straw, mud, etc. This was the theory of spontaneous generation. Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life. He showed that in pre-sterilised flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose from ‘killed yeast’. Spontaneous generation theory was dismissed once and for all. However, this did not answer how the first life form came on earth. Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules (e.g.RNA,protein,etc.)andthatformationoflifewasprecededbychemical evolution, i.e., formation of diverse organic molecules from inorganic constituents. The conditions on earth were – high temperature, volcanic storms,reducingatmospherecontainingCH ,NH ,e4c.In1353,S.L.Miller, an American scientist created similar conditions in a laboratory scale (Figure 6.1). He created electric discharge in a closed flask containing 0 CH ,4H 2 NH a3d water vapour at 800 C. He observed formation of amino acids. In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats. Analysis of meteorite content also revealed similar compounds indicating that similar processes are 111 occurring elsewhere in space. With this limited evidence, the first part of the conjectured story, i.e., chemical evolution was more or less accepted. We have no idea about how the first self replicating metabolic capsule of life arose. The first non-cellular forms of life could have originated 3billionyearsback.Theywouldhavebeengiantmolecules(RNA,Protein, Reprint 2026-27