Miller Urey, while appearing to support spontaneous biogenesis, in actuality indicates the reverse. The model of the atmosphere was incorrect, the Oceanic "primordial soup" has never been shown to exist, the experiment itself was rigged for the production of organic molecules, and the published results were skewed by omitting some of the results.

 The atmosphere of ancient Earth, according to Miller-Urey, was composed of Methane, Ammonia, and Water (with traces of Hydrogen.) This atmosphere is by no means the actual ancient Earth atmosphere: there are at least two other atmospheres that are considered, but are often discluded because of much lower yield of organic molecules. The atmosphere is also thought to have been Carbon Dioxide and Water, or Carbon Dioxide and Nitrogen, both of which are far less reductive, hence were not put to the Miller-Urey experiment.

 R.C. Dowen has said:

 "Now, for the first time in 30 years, the widely accepted recipe for the primordial soup is changing from one rich in hydrogen- composed primarily of methane and ammonia- to a Hydrogen-poor atmosphere similar to today's sans (minus) the Oxygen.

 "No geological or geochemical evidence collected in the last 30 years favors a strongly reducing atmosphere....Only the success of the laboratory experiments recommends it.

 "Scientists are having to rethink some of their assumptions. Chemists liked the old reducing atmosphere, for it was conductive to evolutionary experiments.

Another flaw in the atmosphere is that all exclude oxygen gas. Often Oxygen production is only produced by photosynthesis, but this is really an oversimplification. Oxygen has been known since the 60's to be produced at high altitudes with the effect of ultraviolet light on water in a process known as photolysis. R.T. Brinkman has calculated the bare minimum amount of free oxygen in the atmosphere and has concluded that Earth has always had at least a 5% Oxygen gas atmosphere. Other scientists, who are willing to let uniformitarianism fall by the wayside, compute levels ranging anywhere from 10 to the -1 to 10 to the -15, more or less evenly distributed throughout.

 Now what does a disagreement of 14 powers of ten suggest? It suggests that these scientists haven't got a clue what they are talking about.

 All this does not consider the various "organic" chemicals that were produced by Miller-Urey that impede life. Among the most prevalent of precursor molecules of monomer synthesis is HCN. While HCN is often attributed with much chemical synthesis, such as the amine of amino acids, its mere presence would be fatal to any precursor metabolisms because of cyanide's overkill reductive powers. In short, the monomers would have to form, then all of the HCN decompose to an extremely low level (parts per trillion at least) while still retaining all of the monomers, then and only then could a primitive life form develop. 

 Finally, there is doubt as to whether or not the "primordial soup" that Miller-Urey is designed to emulate. Brooks and Shaw in Origin and Development of Living Systems

 "If there ever was a primitive soup, then we would expect to find at least somewhere on this planet either massive sediments containing enormous amounts of the various nitrogenous organic compounds, amino acids, purines, pyrimidines, and the like, or alternatively in much-metamorphosed sediments we should find vast amounts of nitrogenous cokes. In fact no such materials have been found anywhere on earth.

In the end, while experiments like Miller-Urey may have interesting results, they prove nothing if not linked to physical evidence from atmospheric studies or geochemistry. Primordial soup producing life is a myth that makes the Biblical Flood look docile and credible in comparison.

All references and most thoughts derived from The Mystery of Life's Origin by Charles Thaxton, Walter Bradley, and Roger Olsen.