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-
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → S.L. Miller
The theory of chemical evolution says that the first life was preceded by the formation of organic molecules from inorganic ones. The passage says that in 1953 S.L. Miller created early-earth conditions in a laboratory: an electric discharge in a closed flask of CH4, H2, NH3 and water vapour. He observed the formation of amino acids.
Option (2) S.L. Miller — Correct. S.L. Miller (1953) created conditions like those of early earth in a closed flask: CH4, H2, NH3 and water vapour at 800°C with electric discharge. He observed the formation of amino acids, testing chemical evolution in the laboratory.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.