Life appeared 500 million years after the formation of earth, i.e.. almost four billion years back. Early Greek thinkers thought units of life called spores were transformed to different planets including earth. 'Panspermia' is still a favourite idea of some astronomers. Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life. 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 would have come from pre-existing non-living organic molecules (RNA. proteins etc.) and formation of life was preceded by chemical evolution. i.e.. formation of diverse organic molecules from inorganic constituents. The conditions on earth were - high temperature, volcanic storms, reducing atmosphere containing CH₄. NH₃ etc.In 1953, S.L. Miller, an American scientist, created similar conditions in a laboratory scale. He created electric discharge in a closed flask containing CH₄, H₂, NH₃ and water vapour at 800° C. He observed formation of amino acids. In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats. With this limited evidence, the first part of the conjectured story, i.e.. chemical evolution was more or less accepted.

The theory of Chemical evolution was studied and tested in laboratory by-

S.L. Miller

The correct answer is Option (2) -  S.L. Miller

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.) and that formation of life was preceded by chemical evolution, i.e., formation of diverse organic molecules from inorganic constituents. The conditions on earth were – high temperature, volcanic storms, reducing atmosphere containing CH₄, NH₃, etc.

In 1953, S.L. Miller, an American scientist created similar conditions in a laboratory scale . He created electric discharge in a closed flask containing CH₄, H₂, NH₃ and water vapour at 8000C. 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 occurring elsewhere in space. With this limited evidence, the first part of the conjectured story, i.e., chemical evolution was more or less accepted.