Editing Primordial soup (section)

== Unanswered Questions ==
Though Oparin and Haldane presented a convincing theory for the origin of life, there are some natural phenomena that their work fails to explain. It is understood, based off of the heterotrophic theory, that at the time life was generated, the atmosphere was strongly reducing .<ref>{{Cite book |last=Shapiro |first=Robert Y. |title=Origins: a skeptic's guide to the creation of life on earth |date=1986 |publisher=Summit Books |isbn=978-0-671-45939-0 |location=New York}}</ref><ref>{{Cite journal |last1=Martin |first1=William |last2=Baross |first2=John |last3=Kelley |first3=Deborah |last4=Russell |first4=Michael J. |date=November 2008 |title=Hydrothermal vents and the origin of life |url=https://www.nature.com/articles/nrmicro1991 |journal=Nature Reviews Microbiology |language=en |volume=6 |issue=11 |pages=805–814 |doi=10.1038/nrmicro1991 |pmid=18820700 |bibcode=2008NRvM....6..805M |issn=1740-1526|url-access=subscription }}</ref> However, evidence suggests that the atmosphere was likely not nearly reducing enough to support this.<ref>{{Cite journal |last1=Krupp |first1=Ralf |last2=Oberthuer |first2=Thomas |last3=Hirdes |first3=Wolfgang |date=1994-11-01 |title=The early Precambrian atmosphere and hydrosphere; thermodynamic constraints from mineral deposits |url=http://pubs.geoscienceworld.org/economicgeology/article/89/7/1581/21358/The-early-Precambrian-atmosphere-and-hydrosphere |journal=Economic Geology |language=en |volume=89 |issue=7 |pages=1581–1598 |doi=10.2113/gsecongeo.89.7.1581 |bibcode=1994EcGeo..89.1581K |issn=1554-0774|url-access=subscription }}</ref> The availability of highly reduced compounds such as NH<sub>3</sub> and CH<sub>4</sub> was limited, there was likely not enough of them to support heterotrophic redox and life.<ref name=":1">{{Cite book |last1=Schlesinger |first1=William H. |title=Biogeochemistry: an analysis of global change |last2=Bernhardt |first2=Emily S. |date=2020 |publisher=Academic press, an imprint of Elsevier |isbn=978-0-12-814608-8 |edition=4th |location=London}}</ref>

Another complication with the heterotrophic theory exists due to the selective chirality of biological molecules. Chirality refers to the lack symmetry in biological molecules and which orientation they prefer. For instance, amino acids exist predominantly in the L conformation and sugars prefer the D conformation. Biological molecules are highly specific in which enantiomer they prefer.<ref>{{Cite journal |last1=Ozturk |first1=S. Furkan |last2=Sasselov |first2=Dimitar D. |last3=Sutherland |first3=John D. |date=2023-08-14 |title=The central dogma of biological homochirality: How does chiral information propagate in a prebiotic network? |journal=The Journal of Chemical Physics |language=en |volume=159 |issue=6 |doi=10.1063/5.0156527 |issn=0021-9606 |pmc=7615580 |pmid=37551802|arxiv=2306.01803 |bibcode=2023JChPh.159f1102O }}</ref> Because of this unique fact, scientists feel that the correct theory of the origin of life should explain this selective chirality.<ref name=":1" /> The heterotrophic theory fails to do this.<ref>{{Cite journal |last=Devínsky |first=Ferdinand |date=2021-11-30 |title=Chirality and the Origin of Life |journal=Symmetry |language=en |volume=13 |issue=12 |pages=2277 |doi=10.3390/sym13122277 |doi-access=free |bibcode=2021Symm...13.2277D |issn=2073-8994}}</ref>

The heterotrophic theory is highly specific and includes details about the conditions of early metabolism.<ref>{{Cite journal |last=Lazcano |first=Antonio |date=December 2016 |title=Alexandr I. Oparin and the Origin of Life: A Historical Reassessment of the Heterotrophic Theory |url=http://link.springer.com/10.1007/s00239-016-9773-5 |journal=Journal of Molecular Evolution |language=en |volume=83 |issue=5–6 |pages=214–222 |doi=10.1007/s00239-016-9773-5 |pmid=27896387 |bibcode=2016JMolE..83..214L |issn=0022-2844|url-access=subscription }}</ref> However, in doing this, it is unable to provide a grounds for evolution and the distinction between bacteria, archaea, and eucarya. How did organisms that utilize the same type of metabolism become so highly differentiated?<ref>{{Cite journal |last=Doolittle |first=W. Ford |date=February 2020 |title=Evolution: Two Domains of Life or Three? |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982220300105 |journal=Current Biology |language=en |volume=30 |issue=4 |pages=R177–R179 |doi=10.1016/j.cub.2020.01.010|pmid=32097647 |bibcode=2020CBio...30.R177D }}</ref> This is another unanswered question we are left with if the heterotrophic theory is true.

Finally, as the name implies, the heterotrophic theory indicates that early life on earth consisted entirely of heterotrophs. A condition of heterotrophic metabolism, is that the energetic substrate is not produced by the same organism that consumes it. Because of this, heterotrophy works well in tandem with other species that replenish the depleted substrate.<ref>{{Cite journal |last1=Moran |first1=Mary Ann |last2=Miller |first2=William L. |date=October 2007 |title=Resourceful heterotrophs make the most of light in the coastal ocean |url=https://www.nature.com/articles/nrmicro1746 |journal=Nature Reviews Microbiology |language=en |volume=5 |issue=10 |pages=792–800 |doi=10.1038/nrmicro1746 |issn=1740-1526|url-access=subscription }}</ref> However, if all early life was heterotrophic, there would be no way to regenerate the metabolite needed for energy production.<ref>{{Cite journal |last1=Zakem |first1=Emily J. |last2=Cael |first2=B. B. |last3=Levine |first3=Naomi M. |date=2021-02-09 |title=A unified theory for organic matter accumulation |journal=Proceedings of the National Academy of Sciences |language=en |volume=118 |issue=6 |doi=10.1073/pnas.2016896118 |doi-access=free |issn=0027-8424 |pmc=8017682 |pmid=33536337|bibcode=2021PNAS..11816896Z }}</ref> The heterotrophic theory fails to explain this key fallacy.

Thought the heterotrophic theory is interesting, and could describe elements of early life on earth, it is likely not the whole picture. It must be built upon and developed further to fully explain the niches of early metabolism.