Great excitement was generated by an experiment performed in 1953 by Stanley Miller and Harold Urey. They set up an apparatus containing methane, ammonia and hydrogen gases with water vapour to represent the hypothetical early Earth atmosphere and passed electric sparks through it to simulate lightning strikes. In this reducing atmosphere, the heavy energy input breaks bonds in the gases, and upon cooling bonds reform giving new carbon products. The broken bonds reassociate in a random way such that many different molecules are produced. The most abundant product was tar, but there were also two simple amino acids, glycine and alanine in small quantities. (The amino acid alanine has the formula: CH3CH(NH2)COOH).
Robert Shapiro alludes to his own experiments in which he heated various combinations of organic chemicals together as resulting in a dark, sticky tar. He had hoped to produce the chemistry of life, but ended up with what he describes as a “gunky mess” (Shapiro 1986, page 206). Tar is an organic material with excessive bonding. It is a dead organic material that may originate from life, but it is not helpful to a living organism or as a starting point for life.
Shapiro gives a very good account of the experiments to discover the origin of life that have been conducted over 50 years of the 20th century. However, he concludes that;
“The very best Miller-Urey chemistry, as we have seen, does not take us very far along the path to a living organism. A mixture of simple chemicals, even one enriched in a few amino acids, no more resembles a bacterium than a small pile of real and nonsense words, each written on an individual scrap of paper, resembles the complete works of Shakespeare.” (Shapiro 1986, page 116).
Metabolic processes within cells are catalysed by protein enzymes. It was realized that the formation of macromolecules had to be catalysed by something, and unless life pulled itself up by its own bootstraps these catalysts could not be enzymes. So, it was proposed by A.G. Caines-Smith in 1985 that clay composed of silicates was the catalyst of protometabolism (see footnote).
It was soon realized that since the entire sea could not function as a metabolism, it had to be compartmentalized. It was observed that cell membranes are composed of phospholipids that naturally form spheres when placed in water. So, it was proposed that the protocell was bounded by a very simple lipid membrane that formed spontaneously. The problem with this simple model is that the protocell would be isolated from its environment. The phospholipid membrane of the hypothetical protocell would not allow molecules that fuel metabolism to enter the protocell, nor would it allow toxic waste products out. Isolation from the environment spells non-viability for cells.
The cells we know have a phospholipid bilayer plasma membrane with both embedded and peripheral proteins that regulate the entry and exit of substances into and out of the cytoplasm. The selectively permeable cell membrane maintains a steady internal environment within the cell. Water and some small molecules can cross the phospholipid membrane and follow their concentration gradient, but larger molecules such as glucose and amino acids, and also ions are assisted across the membrane by carrier proteins that are specific to each molecule or ion. Transmembrane proteins include channel proteins, carrier proteins, cell recognition proteins, receptor proteins and enzymatic proteins and transport may be active requiring the expenditure of energy donated by ATP.
The conclusion to this short section is that simple membranes would isolate a cell, making it unable to function as a cell, and complex membranes containing channels and carrier proteins that allow the cell to interact with its environment are complex.
 Cairns-Smith A.G. (1985) Seven Clues to the Origin of Life Cambridge University Press; Cairns-Smith A.G. (1993) Genetic Takeover: And the Mineral Origins of Life Cambridge University Press
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.
As far as the history of ideas is concerned, the notion that life can arise from non-life was linked to the rise of Communism during the 20th century and its atheistic underpinning. It was a necessary corollary to belief in Dialectical Materialism that Soviet scientists find an origin to life that did not involve God. Thus, origin of life theories of the 20th century stepped forward hand in hand with the political ideals of the day.
Soviet scientists claimed that just as Marxism shows that history must drive itself forward towards the triumph of Communism, the beginnings of life drove itself forward towards the colonization of Earth by an imperative logic. Soviet scientists believed that the cytoplasm of the cell contained the means of running the metabolism of the cell (just as the worker’s collectives supposedly ran the Soviet Union). They hotly denied that the genetic material found in the nucleus of the cell contained the program for running the cell. They claimed that the idea that the nucleus runs the cell was part of elitist ideology. DNA had been discovered by scientists in Western Europe and was therefore denounced as a capitalist hypothesis.
It seems that history had the last word, since genes did not go away and Communism fell. However, the idea that life arose by chance or by some natural means that did not involve God remained in circulation and became part of the official dogma of NeoDarwinism.