A British Scientists J.B.S. Haldane(1929) and Russian Scientists Oparin(1924) proposed the theory of origin of life. This theory states that:
i. The lighter elements were present at that time in the atomic form.
ii. As the temperature of the earth decreased the lighter elements combined to form the Water, Methane, Ammonia, Hydrogen molecules and Carbon dioxide.
iii. All these molecules interacted in hot atmosphere of earth and formed sugar, amin acid, alcohol, fatty acid, etc.
iv. By further interaction of these biochemical, some complex organic molecules were formed.
Later the experimental conduct of Stanley Miller and Harold C. Urey in 1953 provided the same atmospheric conditions which existed during the time when life was first forming on the earth. At the end it was concluded that 15% of carbon converted to simple forms of carbon such as ammino acids which formed the proteins.

Stanley L. Miller and Harold C. Urey in 1953 carried an experiment in which they provided exact conditions of the earths atmosphere that use to exist during the generation of life over water. At the time this had molecules like ammonia, methane, and hydrogen sulphide, but no oxygen was present. The temperature was maintained below 100°C and the sparks were passed through the mixture of gas (water vapour, methane, Ammonia, hydrogen molecules and Carbon dioxide) to stimulate lightning. At the end of the experiment after a week, they found that 15% of the carbon (from methane) was converted to simple carbon compounds including amino acids which forms the protein molecules.