Editing Primordial soup (section)

==Oparin's theory==
[[File:Oparin.jpg|thumb|120px|right|Alexander Oparin]]
Alexander Oparin first postulated his theory in Russia in 1924 in a small pamphlet titled ''Proiskhozhdenie Zhizny ''(''The Origin of Life'').<ref name=oparin24>{{cite book | last1 = Oparin| first1 = Alexander Ivanovich | author-link1 = Alexander Oparin| translator1-last = Synge| translator1-first = Ann| year = 1924| chapter = Происхождение жизни| trans-chapter = The Origin of Life| editor1-last = Bernal| editor1-first = John Desmond| editor1-link = John Desmond Bernal| title = The Origin of Life| url = https://books.google.com/books?id=ob6PhrWXZ4gC| series = World natural history| publisher = World Pub. Co.| location = London| pages = 197–234| publication-date = 1967| access-date = 2017-08-15}}</ref> According to Oparin, the primitive Earth's surface had a thick red-hot liquid, composed of heavy elements such as carbon (in the form of [[iron carbide]]). This nucleus was surrounded by the lightest elements, i.e. gases, such as hydrogen. In the presence of water vapour, carbides reacted with hydrogen to form [[hydrocarbons]]. Such hydrocarbons were the first organic molecules. These further combined with oxygen and ammonia to produce hydroxy- and amino-derivatives, such as carbohydrates and proteins. These molecules accumulated on the ocean's surface, becoming gel-like substances and growing in size. They gave rise to primitive organisms (cells), which he called [[coacervate]]s.<ref name="lazcano10"/> In his original theory, Oparin considered oxygen as one of the primordial gases; thus the primordial atmosphere was an oxidising one. However, when he elaborated his theory in 1936 (in a book by the same title, and translated into English in 1938),<ref>{{Cite book|title=The origin of life|last=Oparin|first=Alexander|publisher=MacMillan|year=1938|location=New York}}</ref> he modified the chemical composition of the primordial environment as strictly reducing, consisting of methane, ammonia, free hydrogen and water vapour—excluding oxygen.<ref name="fry"/>

In his 1936 work, impregnated by a Darwinian thought that involved a slow and gradual evolution from the simple to the complex, Oparin proposed a heterotrophic origin, result of a long process of chemical and pre-biological evolution, where the first forms of life should have been microorganisms dependent on the molecules and organic substances present in their external environment.<ref name="lazcano10"/> That external environment was the primordial soup.

The idea of a heterotrophic origin was based, in part, on the universality of fermentative reactions, which, according to Oparin, should have first appeared in evolution due to its simplicity. This was opposed to the idea, widely accepted at that time, that the first organisms emerged endowed with an [[autotrophic]] metabolism, which included [[photosynthetic pigments]], enzymes and the ability to synthesize organic compounds from CO<sub>2</sub> and H<sub>2</sub>O; for Oparin it was impossible to reconcile the original photosynthetic organisms with the ideas of Darwinian evolution.

From the detailed analysis of the geochemical and astronomical data known at that date, Oparin also proposed a primitive atmosphere devoid of O<sub>2</sub> and composed of CH<sub>4</sub>, NH<sub>3</sub> and H<sub>2</sub>O; under these conditions it was pointed out that the origin of life had been preceded by a period of abiotic synthesis and subsequent accumulation of various organic compounds in the seas of primitive Earth.<ref name="Oparin" /> This accumulation resulted in the formation of a primordial broth containing a wide variety of molecules.

There, according to Oparin, a particular type of colloid, the coacervates, were formed due to the conglomeration of organic molecules and other polymers with positive and negative charges. Oparin suggested that the first living beings had been preceded by pre-cellular structures similar to those coacervates, whose gradual evolution gave rise to the appearance of the first organisms.<ref name="Oparin" />

Like the coacervates, several of Oparin's original ideas have been reformulated and replaced; this includes, for example, the reducing character of the atmosphere on primitive Earth, the coacervates as a pre-cellular model and the primitive nature of glycolysis. In the same way, we now understand that the gradual processes are not necessarily slow, and we even know, thanks to the fossil record, that the origin and early evolution of life occurred in short geologic time lapses.

However, the general approach of Oparin's theory had great implications for biology, since his work achieved the transformation of the study of the origin of life from a purely speculative field to a structured and broad research program.<ref name="lazcano10"/> Thus, since the second half of the twentieth century, Oparin's theory of the origin and early evolution of life has undergone a restructuring that accommodates the experimental findings of molecular biology, as well as the theoretical contributions of evolutionary biology.

A point of convergence between these two branches of biology and that has been perfectly incorporated into the heterotrophic origin theory is found in the [[RNA world|RNA world hypothesis]].

This links to the Soda Ocean Hypothesis, characterizing the primitive ocean with a higher carbonate mineral supersaturation.<ref>{{cite book |last1= Kempe |first1= Stephan |last2= Kazmierczak |first2= Józef |date= January 2011 |chapter= Soda Ocean Hypothesis (SOH) |editor= Joachim Reitner and Volker Thiel |title= Encyclopedia of Geobiology |series= Encyclopedia of Earth Sciences Series |pages= 829-832 (see p. 830) |doi= 10.1007/978-1-4020-9212-1_192 |isbn= 978-1-4020-9211-4 |chapter-url= https://www.researchgate.net/publication/299748191
 }}</ref>
[[Soda lake]]s are considered as environments that conserve and/or mimic ancient life conditions<ref>
{{cite journal |last1= Jônatas |first1= Abrahão |last2= Silva |first2= Lorena |last3= Silva |first3= Ludmila Santos |last4= Khalil |first4= Jacques Yaacoub Bou |last5= Rodrigues |first5= Rodrigo |last6= Arantes |first6= Thalita |last7= Assis |first7= Felipe |last8= Boratto |first8= Paulo |last9= Andrade |first9= Miguel |last10= Kroon |first10= Erna Geessien |last11= Ribeiro |first11= Bergmann |last12= Bergier |first12= Ivan |last13= Seligmann |first13= Herve |last14= Ghigo |first14= Eric |last15= Colson |first15= Philippe |last16= Levasseur |first16= Anthony |last17= Kroemer |first17= Guido |last18= Raoult |first18= Didier |last19= Scola |first19= Bernard La |date= 2018 |title= Tailed giant Tupanvirus possesses the most complete translational apparatus of the known virosphere |journal= Nature Communications |volume= 9 |issue= 1 |pages= 749 |doi= 10.1038/s41467-018-03168-1 |pmc= 5829246 |pmid= 29487281 |bibcode= 2018NatCo...9..749A }}
</ref> 
and as "a recreated model of late [[Precambrian]] ocean chemistry"<ref>
{{cite book |last1= Kempe |first1= Stephan |last2= Kazmierczak |first2= Jozef |date= January 1990 |chapter= 5.1. Calcium Carbonate Supersaturation and the Formation of in situ Calcified Stromatolites |editor= Venugopalan Ittekkot, Stephan Kempe, Walter Michaelis, Alejandro Spitzy |title= Facets of Modern Biogeochemistry |type= Festschrift for Egon T. Degens on occasion of his 60th birthday |location= Berlin, Heidelberg, New York |publisher= Springer-Verlag |pages= 255-278 (see p. 275) |doi= 10.1007/978-3-642-73978-1_21 |doi-broken-date= 1 November 2024 |isbn= 978-3-642-73980-4 |chapter-url= https://www.researchgate.net/publication/285579127
 }}
</ref> — that is, the "soda lake" environment that prepared the great explosion of life during the [[Cambrian]].