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===Miller-Urey experiment===
Main article: [[Miller-Urey experiment]]
[[File:MillerUreyExperiment.PNG|300px|thumb|right|The setup of the Miller-Urey Experiment of 1953. It attempted to simulate primitive Earth gases (Methane, Ammonia, Hydrogen, Water Vapor), primitive oceans (Water), and lightning.]]
In 1953 American chemist Stanley Miller under the supervision of American scientist Harold C. Urey at the University of Chicago performed an experiment that tried to produce components that attempted to replicate the conditions of Earth’s early atmosphere and oceans to test whether organic molecules could be created abiotically (from inorganic molecules).<ref name="Brit">[https://www.britannica.com/science/Miller-Urey-experiment Miller-Urey experiment] Encyclopedia Britannica</ref>
====Early earth atmosphere====
There is significant uncertainty to what the primitive atmosphere was composed of.<ref name="Bada2013" /> The Miller-Urey experiment assumed an a primitive atmosphere was composed of ''reducing'' (oxygen poor) gases [e.g. methane (CH<sub>4</sub>), ammonia (NH<sub>3</sub>), hydrogen (H<sub>2</sub>), and water vapor (H<sub>2</sub>O)], but by the 1980s geochemists believed that early earth atmospheres probably had ''neutral'' gases like those emitted by volcanoes [e.g. water vapor (H<sub>2</sub>O), carbon dioxide (CO<sub>2</sub>), and nitrogen (N<sub>2</sub>)] and perhaps some ''reducing'' gases like carbon monoxide (CO). Since hydrogen was a light element, there probably would not have been any or perhaps very little in early earth.<ref name="wells" /><ref name="Bada2013">Bada JL. [https://web.archive.org/web/20190225141103id_/http://pdfs.semanticscholar.org/6f46/3e8a3611fa7f25c143991dfddac49c396b73.pdf New insights into prebiotic chemistry from Stanley Miller's spark discharge experiments]. Chem Soc Rev. 2013 Mar 7;42(5):2186-96. doi: 10.1039/c3cs35433d</ref><ref name="wells">Jonathan Wells. 2017. Zombie Science: More Icons of Evolution. ISBN: 978-1936599448. 3. Survival of the Fakest</ref> A possible source of lightning could have been "volcanic lightning", which occurs sometimes near volcanic eruption plumes, and some volcanic gases emitted have been hydrogen sulfide (H<sub>2</sub>S), ammonia (NH<sub>3</sub>), methane (CH<sub>4</sub>), and carbon dioxide (CO<sub>2</sub>).<ref name="Bada2013" /> Some scientists believe that early earth atmosphere was similar to earth today.<ref>[https://web.archive.org/web/20250902132614/https://astrobiology.nasa.gov/news/earths-early-atmosphere-an-update/ Earth's Early Atmosphere: An Update] - NASA</ref>
====Hydrothermal vents====
Hydrothermal vents have been prosed as an alternative source of prebiotic compounds like amino acids, but they face significant limitations. For example, vent systems tend to have very short lives of about 100-10,000 years.<ref name="Bada2013" />
====Limited time frames for prebiotic synthesis====
Scientists believe that there was a time limit for meteorites for form simple to slightly more complex compounds: greater than 1,000 to less than 1,000,000 years.<ref name="Bada2013" /> This poses a problem for hydrothermal vents since they have a very short life span of 100-10,000 years.<ref name="Bada2013" /> Leading Miller-Urey experiment researcher Jeffrey Bada admits
"An important issue is whether these timescales are compatible with the time required for the transition from abiotic to biotic chemistry. As noted, in carbonaceous meteorites the timescale for amino acid production is between >10<sup>3</sup> to <10<sup>6</sup> years, perhaps even as short as 1–10 years, and there is no evidence that the prebiotic chemistry that took place on the meteorite parent bodies during this aqueous alteration period produced anything beyond simple monomeric compounds. It has been suggested that catalysts such as metal sulfides present in vent systems would promote more rapid synthesis, but by the principle of microscopic reversibility, these must also catalyze the decomposition of any synthesized compounds. Moreover, if this was the case there are certainly potential metal catalysts present on meteorite parent bodies and, as has been indicated, nothing beyond simple molecules were apparently synthesized."
====Chemical yield of amino acids====
Amino acid yield in spark discharge experiments depends critically on the pH of the aqueous phase since at lower pH, amino acid production is greatly reduced and hydroxy acids in greatly increased.<ref name="Bada2013" /> Hydrothermal vents have been proposed as an alternative prebiotic chemistry source but they face severe limitations and actual synthesis have never been demonstrated using plausible geochemical conditions.<ref name="Bada2013" />
===Requirements for non-living chemicals to become living===
* To control cascades of chemical reactions (e.g., metabolism), resulting in growth to maturity, steady-state maintenance, defense against predators and chemical deterioration, energy- conversion processes, reproduction, followed by a more-or-less rapid senescence and expiry"
==Problems Chemical problems facing abiogenesis==
[[File:Francis_Crick.jpg|thumb|right|thumbnail|200px|[[Francis Crick]] ]]
The attempt to explain the origin of life faces numerous difficult problems which is why the theory has not fared well in recent times:
