The concept of a biochemical origin of life was first proposed by Russian biochemist A.I. Oparin in 1923 and later supported by English scientist J.B.s Haldane in 1928. Thus, this theory is also called Oparin and Haldane theory. They believed the origin of life started along the origin and evolution of earth and atmosphere. As Biochemical origin of life is complex phenomenon it can be studied in three phases;
Origin of earth and its atmosphere
Formation of simple molecules
2H2+ O2→ 2H2O
N2+ 3H2→ 2NH3
C +2H2→ CH4
Formation of simple organic compounds
On the further cooling variety of saturated and unsaturated hydrocarbons were formed which reacted with hot water vapour to form small chain compounds like ketones, alcohols and other organic acids.
Under the influence of UV rays radiation, electricity from the thunderstorm, volcanic eruption etc simple molecules converted into simple organic compounds like sugar, amino acid, purine and pyrimidine.
CH4 + H2O→ sugar, fatty acid, glycerol
CH4 + H2O + NH3→ Aminoacid
CH4 + H2O + NH3+ HCN→Purine + Pyrimidine
The hot water ocean containing organic compounds was described by Haldane as "The Hot Dilute Soup" or "The Primordial soup" or "Prebiotic soup". Darwin called it as "Warm little poud".
Formation of complex organic compounds
The simple organic compounds were polymerised to form complex organic compounds like polysaccharides, polypeptides, proteins, lipids etc. There was a large number of complex organic compounds in ocean remained to unspoil due to the absence of life. There was the formation of nucleotides by the combination of sugar, phosphate, purine and pyrimidine. Nucleotides formed nucleic acid which is the basic component of life.
Formation of coacervates
The complex organic compounds of primordial soup in ocean aggregated together through the colloidal system and bounded by water layer was called coacervates. They can grow by absorbing nutrients.
Coacervates may produce the first cell-like structure. The first cell-like structure with the power of division is called Eabiant or Pre-cell. Oparin called it as protobiont.
The coacervates which acquired nucleoproteins gave first cellular structures. Their limiting membranes were formed by fatty acids and showed the great affinity with water. Some of the proteins within coacervates acted as enzymes and began metabolic activities. In this way, first prokaryotic, unicellular, heterotrophs, anaerobic organism evolved.