(1) The primitive sea containing molecules of organic substances without free oxygen was described as ‘hot dilute soup or primitive broth’ by Haldane. He proposed the theory of chemical evolution.
(2) According to this theory, the chemical evolution took place in the following steps :
(a) Origin of earth and its primitive atmosphere,
(b) Formation of ammonia, water and methane. These molecules dissolved in rainwater and formed the seas,
(c) Then synthesis of simple organic compounds took place, followed by formation of complex organic compounds such as nucleic acids.
(3) The early molecules underwent chemical reactions such as condensation, polymerization, oxidation and reduction.
(4) The biologically important molecules such as monosaccharides, amino acids, purine, pyrimidine, fatty acids and glycerol were formed due to these reactions, utilizing the sources of energy on the primitive earth.
(5) Since oxygen was lacking, there was no degradation. Enzymes were also absent and hence there was formation of complex molecules in the hot dilute soup.
(6) This further led to the formation of precells or protobiont. These aggregates were called coacervates by Oparin or microspheres by Sidney Fox. This further gave rise to first cells on the earth.
