Editing Miller–Urey experiment (section)

=== Foundations of organic synthesis and the origin of life ===
{{See also|History of research into the origin of life}}Until the 19th century, there was considerable acceptance of the theory of [[spontaneous generation]], the idea that "lower" animals, such as insects or rodents, arose from decaying matter.<ref>{{Cite book |last=Sheldon |first=Robert B. |title=Astrobiology and Planetary Missions |date=2005-08-18 |editor-last=Hoover |editor-first=Richard B. |editor2-last=Levin |editor2-first=Gilbert V. |editor3-last=Rozanov |editor3-first=Alexei Y. |editor4-last=Gladstone |editor4-first=G. Randall |chapter=Historical development of the distinction between bio- and abiogenesis |volume=5906 |chapter-url=http://proceedings.spiedigitallibrary.org/proceeding.aspx?doi=10.1117/12.663480 |pages=444–456 |doi=10.1117/12.663480|s2cid=44194609 }}</ref> However, several experiments in the 19th century – particularly [[Louis Pasteur]]'s [[swan neck flask]] experiment in 1859<ref>{{Cite web |date=2022-05-27 |title=Pasteur's "col de cygnet" (1859) {{!}} British Society for Immunology |url=https://www.immunology.org/pasteurs-col-de-cygnet-1859 |access-date=2023-11-11 |archive-url=https://web.archive.org/web/20220527024603/https://www.immunology.org/pasteurs-col-de-cygnet-1859 |archive-date=2022-05-27 }}</ref> — disproved the theory that life arose from decaying matter. [[Charles Darwin]] published ''[[On the Origin of Species]]'' that same year, describing the mechanism of [[Evolution|biological evolution]].<ref>{{Cite book |last=Darwin |first=Charles |title=On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life |publisher=John Murray |year=1859 |location=London}}</ref> While Darwin never publicly wrote about the first organism in his theory of evolution, in a letter to [[Joseph Dalton Hooker]], he speculated:<blockquote>But if (and oh what a big if) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts, light, heat, electricity etcetera present, that a protein compound was chemically formed, ready to undergo still more complex changes [...]"<ref>Darwin, Charles. Darwin Correspondence Project, "Letter No. 7471", 1871. Available online: http://www.darwinproject.ac.uk/DCP-LETT-7471</ref></blockquote>
[[File:Oparin.jpg|left|thumb|258x258px|Portrait photograph of Alexander Oparin]]
At this point, it was known that organic molecules could be formed from inorganic starting materials, as [[Friedrich Wöhler]] had described [[Wöhler synthesis]] of [[urea]] from [[ammonium cyanate]] in 1828.<ref>Friedrich Wöhler (1828). "Ueber künstliche Bildung des Harnstoffs". Annalen der Physik und Chemie. 88 (2): 253–256</ref> Several other early seminal works in the field of [[organic synthesis]] followed, including [[Alexander Butlerov]]'s [[Butlerov reaction|synthesis of sugars]] from [[formaldehyde]] and [[Adolph Strecker]]'s synthesis of the amino acid [[alanine]] from [[acetaldehyde]], [[ammonia]], and [[hydrogen cyanide]].<ref name="Miller">Miller, S. L., & Cleaves, H. J. (2006). Prebiotic chemistry on the primitive Earth. ''Systems biology'', ''1'', 1.</ref> In 1913, Walther Löb synthesized amino acids by exposing [[formamide]] to [[Dielectric barrier discharge|silent electric discharge]],<ref>Löb, W. (1913). Über das Verhalten des Formamids unter der Wirkung der stillen Entladung Ein Beitrag zur Frage der Stickstoff'''''‐'''''Assimilation. ''Berichte der deutschen chemischen Gesellschaft'', ''46''(1), 684–697.</ref> so scientists were beginning to produce the building blocks of life from simpler molecules, but these were not intended to simulate any prebiotic scheme or even considered relevant to origin of life questions.<ref name="Miller" />

But the scientific literature of the early 20th century contained speculations on the origin of life.<ref name="Miller" /><ref>{{Cite book |title=Life's origin: the beginnings of biological evolution |date=2002 |publisher=Univ. of California Press |isbn=978-0-520-23391-1 |editor-last=Schopf |editor-first=J. William |location=Berkeley, Calif.}}</ref> In 1903, physicist [[Svante Arrhenius]] hypothesized that the first microscopic forms of life, driven by the [[radiation pressure]] of stars, could have arrived on Earth from space in the [[panspermia]] hypothesis.<ref>[[Svante Arrhenius|Arrhenius, Svante]] (1903). "Die Verbreitung des Lebens im Weltenraum" [The Distribution of Life in Space]. ''Die Umschau.''</ref> In the 1920s, [[Leonard T. Troland|Leonard Troland]] wrote about a primordial [[enzyme]] that could have formed by chance in the [[Paleoceanography|primitive ocean]] and catalyzed reactions, and [[Hermann Joseph Muller|Hermann J. Muller]] suggested that the formation of a [[gene]] with catalytic and autoreplicative properties could have set evolution in motion.<ref>{{Cite journal |last=Lazcano |first=A. |date=2010-11-01 |title=Historical Development of Origins Research |journal=Cold Spring Harbor Perspectives in Biology |language=en |volume=2 |issue=11 |pages=a002089 |doi=10.1101/cshperspect.a002089 |issn=1943-0264 |pmc=2964185 |pmid=20534710}}</ref> Around the same time, Alexander Oparin's and J. B. S. Haldane's "[[Primordial soup]]" ideas were emerging, which hypothesized that a [[Reducing atmosphere|chemically-reducing atmosphere]] on early Earth would have been conducive to organic synthesis in the presence of sunlight or lightning, gradually concentrating the ocean with random organic molecules until life emerged.<ref>{{Citation |last1=Kumar |first1=Dhavendra |title=Cosmic Genetic Evolution |date=2020 |series=Advances in Genetics |volume=106 |pages=xv–xviii |publisher=Elsevier |language=en |doi=10.1016/s0065-2660(20)30037-7 |isbn=978-0-12-821518-0 |pmc=7568464 |pmid=33081930 |last2=Steele |first2=Edward J. |last3=Wickramasinghe |first3=N. Chandra|chapter=Preface: The origin of life and astrobiology }}</ref> In this way, frameworks for the origin of life were coming together, but at the mid-20th century, hypotheses lacked direct experimental evidence.