Oparin and Haldane  formulated the theory of chemical evolution.

According to chemical theory of origin of life, a long evolution of chemical substances preceded the actual origin of life. The various steps are:

Formation of inorganic molecules from atoms by the cooling of earth's atmosphere and utilizing sun's energy.Spontaneous formation of simple organic molecules like sugars, fatty acids, amino acids etc. from the primitive inorganic molecules.The accumulation of organic molecules due to lack of life and reducing atmosphere.Further, these organic molecules synthesized all the compounds known to exist in living objects.