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46 GulO®@OG, , , , 8:18 PM ins a), , , , < Part12EVOL.. @ & :, , ‘Monika Irengbam, , CHAPTER 7- EVOLUTION, Definition: Evolutionary biology is the study of history of life from on earth., ORIGIN OF LIFE:, 1. The universe is about 20 billion years old . Huge cluster of galaxies became universe which, contained stars and clouds of gas and dust ., , 2. The Big bang theory : This theory explains the origin of universe in which single explosion had, occurred and universe expanded when temperature came down. Hydrogen , Helium form, later . The gases condensed under gravitation and formed galaxies of present day in the solar, system of milky way galaxy earth was formed 4.5 billion years back. At that time no, atmosphere was present , water vapour , methane , carbon dioxide and ammonia released, from molten mass covered the surface , ultra violet rays from the sun broke up water into, Hydrogen and Oxygen and lightest H2 escaped., , 3. Greek thinker thought life came from spores and was transferred to different planets, including earth . Panspermia idea was favorite for astronomer and believed that life came, from decaying matter like straw , mud etc. This theory is known as theory of spontaneous, generation . Louis Pasteur demonstrated that life can from pre ~existings life . He showed in, pre sterlised flask life , did not came from killed yeast while in another flask open to air, new, theory organism was from yeast . So this theory of spontaneous generation was discovered, , 4 .Oparin of Russia and Halden of England life came from preexisting organic molecules , which, was followed by chemical evolution., The conditions earth were high temperature , volcanic storms , reducing atmosphere CH4,, NH3 etc. discharge in a closed flask containing CH4, H2 ,NH3 and water vapour at 100, degree celcius .The first non- cellular forms of life could have originated 3 million years, back., , Giant molecules ( RNA , protein , polysaccharide etc. ) were formed .These molecules can, reproduce perhaps, , First originated life were single cells and were in water in which is known as biogenesis ~ ie, First from of life arose from non -living molecules and is accepted by all., , ‘Theories of Evolution : The theory of special creation was challenged by Charles Darwin who made, ‘observation on his sea— trip around world in H.M.S. BEAGLE and concluded that all living, ‘organism share come similarities among themselves which exists million of years ago and, became extinct, __ The evolution of life forms has been gradual and those life form fit in environment that, leads to progeny which is called natural Selection and is mechanism of evolution ., _This above theory was also concluded by Alfred Wallace ., , , , Evidences of Evolution:, Fossil :, , , , ‘rom fossils we know that plants and animals lived millions years ago and are extinct . So different, , aged rock contains sediments of fossils of different life forms that were existed . Comparative, , o, , I, (), u