Editing Miller–Urey experiment (section)

=== Modified Miller–Urey experiments ===
Much work has been done since the 1950s toward understanding how Miller-Urey chemistry behaves in various environmental settings. In 1983, testing different atmospheric compositions, Miller and another researcher repeated experiments with varying proportions of H<sub>2</sub>, H<sub>2</sub>O, N<sub>2</sub>, CO<sub>2</sub> or CH<sub>4</sub>, and sometimes NH<sub>3</sub>.<ref name="Miller-1983">{{Cite journal |last1=Miller |first1=Stanley L. |last2=Schlesinger |first2=Gordon |date=1983-01-01 |title=The atmosphere of the primitive earth and the prebiotic synthesis of organic compounds |url=https://dx.doi.org/10.1016/0273-1177%2883%2990040-6 |journal=Advances in Space Research |volume=3 |issue=9 |pages=47–53 |doi=10.1016/0273-1177(83)90040-6 |pmid=11542461 |bibcode=1983AdSpR...3i..47M |issn=0273-1177}}</ref> They found that the presence or absence of NH<sub>3</sub> in the mixture did not significantly impact amino acid yield, as NH<sub>3</sub> was generated from N<sub>2</sub> during the spark discharge.<ref name="Miller-1983" /> Additionally, CH<sub>4</sub> proved to be one of the most important atmospheric ingredients for high yields, likely due to its role in HCN formation.<ref name="Miller-1983" /> Much lower yields were obtained with more oxidized carbon species in place of CH<sub>4</sub>, but similar yields could be reached with a high H<sub>2</sub>/CO<sub>2</sub> ratio.<ref name="Miller-1983" /> Thus, Miller-Urey reactions work in atmospheres of other compositions as well, depending on the ratio of reducing and oxidizing gases. More recently, [[Jeffrey L. Bada|Jeffrey Bada]] and H. James Cleaves, graduate students of Miller, hypothesized that the production of nitrites, which destroy amino acids, in CO<sub>2</sub> and N<sub>2</sub>-rich atmospheres may explain low amino acids yields.<ref name="Cleaves-2008">{{Cite journal |last1=Cleaves |first1=H. James |last2=Chalmers |first2=John H. |last3=Lazcano |first3=Antonio |last4=Miller |first4=Stanley L. |last5=Bada |first5=Jeffrey L. |date=2008 |title=A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres |url=http://link.springer.com/10.1007/s11084-007-9120-3 |journal=Origins of Life and Evolution of Biospheres |language=en |volume=38 |issue=2 |pages=105–115 |doi=10.1007/s11084-007-9120-3 |pmid=18204914 |bibcode=2008OLEB...38..105C |s2cid=7731172 |issn=0169-6149}}</ref> In a Miller-Urey setup with a less-reducing (CO<sub>2</sub> + N<sub>2</sub> + H<sub>2</sub>O) atmosphere, when they added [[calcium carbonate]] to [[Buffer (chemistry)|buffer]] the aqueous solution and [[Chemistry of ascorbic acid|ascorbic acid]] to inhibit oxidation, yields of amino acids greatly increased, demonstrating that amino acids can still be formed in more neutral atmospheres under the right [[Geochemistry|geochemical]] conditions.<ref name="Cleaves-2008" /> In a prebiotic context, they argued that seawater would likely still be buffered and [[Iron(II) compounds|ferrous iron]] could inhibit oxidation.<ref name="Cleaves-2008" />

In 1999, after Miller suffered a stroke, he donated the contents of his laboratory to Bada.<ref name="Dreifus-2010" /> In an old cardboard box, Bada discovered unanalyzed samples from modified experiments that Miller had conducted in the 1950s.<ref name="Dreifus-2010" /> In a "[[Volcano|volcanic]]" apparatus, Miller had amended an aspirating nozzle to shoot a jet of steam into the reaction chamber.<ref name="bada20132" /><ref name="Johnson-2008">{{Cite journal |last1=Johnson |first1=Adam P. |last2=Cleaves |first2=H. James |last3=Dworkin |first3=Jason P. |last4=Glavin |first4=Daniel P. |last5=Lazcano |first5=Antonio |last6=Bada |first6=Jeffrey L. |date=2008-10-17 |title=The Miller Volcanic Spark Discharge Experiment |url=https://www.science.org/doi/10.1126/science.1161527 |journal=Science |language=en |volume=322 |issue=5900 |pages=404 |doi=10.1126/science.1161527 |pmid=18927386 |bibcode=2008Sci...322..404J |s2cid=10134423 |issn=0036-8075}}</ref> Using [[high-performance liquid chromatography]] and [[mass spectrometry]], Bada's lab analyzed old samples from a set of experiments Miller conducted with this apparatus and found some higher yields and a more diverse suite of amino acids.<ref name="bada20132" /><ref name="Johnson-2008" /> Bada speculated that injecting the steam into the spark could have split water into H and OH radicals, leading to more [[Hydroxylation|hydroxylated]] amino acids during Strecker synthesis.<ref name="bada20132" /><ref name="Johnson-2008" /> In a separate set of experiments, Miller added [[hydrogen sulfide]] (H<sub>2</sub>S) to the reducing atmosphere, and Bada's analyses of the products suggested order-of-magnitude higher yields, including some amino acids with [[sulfur]] [[Moiety (chemistry)|moieties]].<ref name="bada20132" /><ref name="Parker-2011">{{Cite journal |last1=Parker |first1=Eric T. |last2=Cleaves |first2=Henderson J. |last3=Dworkin |first3=Jason P. |last4=Glavin |first4=Daniel P. |last5=Callahan |first5=Michael |last6=Aubrey |first6=Andrew |last7=Lazcano |first7=Antonio |last8=Bada |first8=Jeffrey L. |date=2011-04-05 |title=Primordial synthesis of amines and amino acids in a 1958 Miller H 2 S-rich spark discharge experiment |journal=Proceedings of the National Academy of Sciences |language=en |volume=108 |issue=14 |pages=5526–5531 |doi=10.1073/pnas.1019191108 |issn=0027-8424 |pmc=3078417 |pmid=21422282 |doi-access=free }}</ref>

A 2021 work highlighted the importance of the high-energy free electrons present in the experiment. It is these electrons that produce ions and radicals, and represent an aspect of the experiment that needs to be better understood.<ref>{{Cite journal |last1=Micca Longo |first1=Gaia |last2=Vialetto |first2=Luca |last3=Diomede |first3=Paola |last4=Longo |first4=Savino |last5=Laporta |first5=Vincenzo |date=2021-06-16 |title=Plasma modeling and prebiotic chemistry: A review of the state-of-the-art and perspectives |journal=Molecules |language=en |volume=26 |issue=12 |pages=3663 |doi=10.3390/molecules26123663 |doi-access=free|pmid=34208472 |pmc=8235047 }}</ref>

After comparing Miller–Urey experiments conducted in [[borosilicate glass]]ware with those conducted in [[Polytetrafluoroethylene|Teflon]] apparatuses, a 2021 paper suggests that the glass reaction vessel acts as a mineral [[Catalysis|catalyst]], implicating silicate rocks as important surfaces in prebiotic Miller-Urey reactions.<ref>{{Cite journal |last1=Criado-Reyes |first1=Joaquín |last2=Bizzarri |first2=Bruno M. |last3=García-Ruiz |first3=Juan Manuel |last4=Saladino |first4=Raffaele |last5=Di Mauro |first5=Ernesto |date=2021-10-25 |title=The role of borosilicate glass in Miller–Urey experiment |journal=Scientific Reports |language=en |volume=11 |issue=1 |pages=21009 |doi=10.1038/s41598-021-00235-4 |bibcode=2021NatSR..1121009C |issn=2045-2322|doi-access=free |pmid=34697338 |pmc=8545935 }}</ref>