Primordial soup
[1][2] As formulated by Oparin, in the primitive Earth's surface layers, carbon, hydrogen, water vapour, and ammonia reacted to form the first organic compounds.
The concept of a primordial soup gained credence in 1953 when the "Miller–Urey experiment" used a highly reduced mixture of gases—methane, ammonia and hydrogen—to form basic organic monomers, such as amino acids.
His theory remained the dominant idea on origin of life (outside that of deity as a causal agent) from the ancient philosophers to the Renaissance thinkers in various forms.
But if (and oh what a big if) we could conceive in some warm little pond with all sort of ammonia and phosphoric salts,—light, heat, electricity present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present such matter would be instantly devoured, or absorbed, which would not have been the case before living creatures were formed [...].A coherent scientific argument was introduced by Soviet biochemist Alexander Oparin in 1924.
[15] According to Oparin, the primitive Earth's surface had a thick red-hot liquid, composed of heavy elements such as carbon (in the form of iron carbide).
However, when he elaborated his theory in 1936 (in a book by the same title, and translated into English in 1938),[16] he modified the chemical composition of the primordial environment as strictly reducing, consisting of methane, ammonia, free hydrogen and water vapour—excluding oxygen.
Oparin suggested that the first living beings had been preceded by pre-cellular structures similar to those coacervates, whose gradual evolution gave rise to the appearance of the first organisms.
In the same way, we now understand that the gradual processes are not necessarily slow, and we even know, thanks to the fossil record, that the origin and early evolution of life occurred in short geologic time lapses.
However, the general approach of Oparin's theory had great implications for biology, since his work achieved the transformation of the study of the origin of life from a purely speculative field to a structured and broad research program.
A point of convergence between these two branches of biology and that has been perfectly incorporated into the heterotrophic origin theory is found in the RNA world hypothesis.
A graduate student, Stanley Miller, and his professor, Harold Urey, performed an experiment that demonstrated how organic molecules could have spontaneously formed from inorganic precursors, under conditions like those posited by the Oparin–Haldane hypothesis.
Apart from the Miller–Urey experiment, the next most important step in research on prebiotic organic synthesis was the demonstration by Joan Oró that the nucleic acid purine base, adenine, was formed by heating aqueous ammonium cyanide solutions.
[22] In support of abiogenesis in eutectic ice, more recent work demonstrated the formation of s-triazines (alternative nucleobases), pyrimidines (including cytosine and uracil), and adenine from urea solutions subjected to freeze-thaw cycles under a reductive atmosphere (with spark discharges as an energy source).
[24] The basic conditions necessary for natural selection to operate as conceived by Darwin are variation of type, heritability and competition for limited resources.
[25] The basic processes of natural selection applicable to short replicating RNA molecules were shown to have the same form and content as equations that govern the emergence of macroscopic order in nonliving systems maintained far from thermodynamic equilibrium.
