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Miller-Urey experiment (view source)
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===Early earth atmosphere===
===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" /> 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>
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" /> 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>
====Chemical Yield====
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" />
==See also==
==See also==