10 Critiques of Miller-Urey Experiments : Abiogenesis, Primordial Soup, and Origin of Life Theory Reviewed and Refuted
That’s about the only good news astrobiologists can expect, though, because all the old criticisms of the Miller experiment by Jonathan Wells still apply:
(1) They still used the wrong gasses: methane, ammonia, and water vapor. For decades, geochemists have not considered it likely these gasses were abundant in the early Earth atmosphere.
(2) They still ignored the presence of oxygen, which destroys the desired products. Wells explained that oxygen was likely abundant due to photodissociation of water in the atmosphere. The oxygen would remain, while the hydrogen would quickly escape to space.
(3) Even if trace amounts of ammonia or methane and other reducing gasses were present, they would have been rapidly destroyed by ultraviolet radiation.
(4) No amino acids have been generated in spark-discharge experiments using a realistic atmosphere of nitrogen, carbon dioxide and water vapor, even in the absence of oxygen.
To this we could add more problems:
(5) The amino acids produced were racemic (mixtures of left- and right-handed forms). Except in rare exceptions, life uses only the left-handed form. Astrobiologists need to explain how the first replicator isolated one hand out of the mixture, or obtained function from mixed-form amino acids initially, then converted to single-handed forms later. Neither is plausible for unguided natural processes — especially when natural selection would be unavailable until accurate replication was achieved.
(6) Undesirable cross-reactions with other products would generate tar, destroying the amino acids. Only by isolating the desired products (a form of investigator interference — one might call it intelligent design) could they claim partial success.
(7) Amino acids tend to fall apart in water, not join. Under the best conditions with cyanamide, Bada and Parker only got dipeptides. Repeated cycles of wetting and drying would need to be imagined for polymerization, but many astrobiologists today think life originated at deep sea hydrothermal vents.
(8) The desired reagents would be extremely dilute in the oceans without plausible concentrating mechanisms. Even then, they would disperse without plausible vessels, like cell membranes, to keep them in proximity.
(9) Lifeless polypeptides would go nowhere without a genetic code to direct them.
(10) The Miller experiments cannot speak to the origin of other complex molecules needed by life: nucleic acids, sugars, and lipids. Some of these require vastly different conditions than pictured for amino acid synthesis: e.g., a desert environment with boron for the synthesis of ribose (essential for RNA).
If you want to want to go even deeper, I would suggest watching the following from ARN: Abiogenesis: The Faith and the Facts