$2000$ million years.

Experimental Evidences of Chemical Evolution

Experi ik mentally chemical theory of evolution performed by SL Miller and HC Uray in $1953 .$

He created electric discharge in a closed flask containing $CH _{4}, H _{2}, N H _{3}$ and water vapour at $800\, C .$ He observed formation of amino acids. In similar experiments other the observed, formation of sugar, nitrogen bases, pigments and fats

The first non-cellular forms of life could have originated-$3$ billion years back. The first cellular form of life did not possibly originated till about $2$ billion years ago because the conditions were non-biogenic at that time. This version of biogenesis, $i.e.,$ the first form of life arose slowly through evolutionary forces from non-living molecule was accepted by majority