There are many ancient theories which try to explain the origin of life. Theory of special creation states that all forms of life are created by a supernatural power, God. The greatest supporter of special creation theory was Father Suarez.
Oparin and Haldane proposed that life on earth could have originated from the non-living organic molecules (example, RNA and protein). The ultraviolet radiations from the sun and the reducing atmosphere favoured the chemical reactions on the primitive earth that led to the formation of simple organic molecules like amino acids, sugars and nitrogenous bases.
Based on the hypothesis given by Oparin and Haldane, Stanley Miller conducted an experiment which provided evidence of chemical evolution.