The Primeval Soup Theory for the origin of life on Earth was first proposed by J. B. S. Haldane (1892-1964), a British Marxist biologist who lived in the USA and Britain, and Alexander Oparin (1894-1980) of the USSR. It is the idea that life arose from inorganic matter under conditions proposed as having existed on the early Earth, but not existing now.
There are various versions of the Primeval Soup Theory differing in some details. All must include a reducing atmosphere since organic macromolecules will not form naturally without it. Hence it is proposed that the atmosphere of the early Earth was composed of methane, ammonia and hydrogen. There was a sea of water formed from condensed water vapour. The energy which would trigger the emergence of life came from flashes of lightning, ultraviolet radiation or even meteorite impact. The effect of the light or heat energy on the atmosphere of strange gases would be the formation of organic, carbon-based molecules that would accumulate in the water which thus became a prebiotic soup.
It is now known that if the early atmosphere was so reducing that it did not contain any carbon dioxide, then the Earth would have been covered with ice. The discovery of the exotic world of hydrothermal vents then led to the hypothesis that life emerged in one of the places on Earth that had reducing conditions in a limited location.
The primeval soup would contain carbohydrates the components of sugars; amino acids the components of proteins; and nucleotides the components of DNA and RNA. Thus, it is proposed in the Primeval Soup Theory that all the ingredients of life were present as building blocks on early Earth. It has been observed that the building blocks of life do combine with each other in predictable ways. At this point the Natural Selection argument is used to explain that little organic molecules (monomers) have an advantage if they become big organic molecules (polymers) and if they learn to self-replicate. The survival of the fittest idea is applied to molecules, which form themselves into a protometabolism whose function is to form new types of molecules. The idea of the evolution of macromolecules was proposed by Francis Crick and Leslie E. Orgel in 1973.
Robert Shapiro points out that the proposed compositions of the atmosphere of early Earth and the ‘soup’ are hypothetical, and may never have existed at all. He also points out that the water of this ocean would prevent the formation of biological macromolecules since water prises nucleotides apart from each other by breaking sugar-phosphate bonds and severing bases from sugars (Shapiro 1986, pages 173-174). Thus, DNA and RNA macromolecules in water become nucleotide small molecules. Also, in the presence of water peptide polymers and proteins slowly break down into their amino acid components.
It seems that, whereas in the world of speculation, ‘Natural Selection’ as the driver builds up complex molecules, in the real world thermodynamics breaks down complex molecules into simpler ones.