Miller-Urey and the Early Atmosphere

Cleaves, H. James et al.  “A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres.”  Origins of Life and Evolution of Biospheres 38:105–115.  2008.  “When the reaction was buffered with CaCO₃, the pH of the aqueous phase after sparking was 7.1… the amino acid yields increased 2–15 fold.”  “Ascorbic acid is an unlikely prebiotic anti-oxidant.  However, oxidation could have been inhibited by other available chemical species such as sulfides and reduced metal ions… Only pyrites (10× over control recovery) and FeSO₄ (2× over control recovery) were found to be able to protect against degradation to a significant degree using this molar ratio of reactants.”  Section Abstract:  “We show here that contrary to previous reports, significant amounts of amino acids are produced from neutral gas mixtures.  The low yields previously reported appear to be the outcome of oxidation of the organic compounds during hydrolytic workup by nitrite and nitrate produced in the reactions.  The yield of amino acids is greatly increased when oxidation inhibitors, such as ferrous iron, are added prior to hydrolysis.”  Table 2:  Yields of total hydrolysable amino acids on input N2: CO2/N2 unbuffered 0.013% without ascorbate and 1.3% with; CO2/N2/CaCO3 0.19% and 2.5%.  The table's own footnote gives the reducing-atmosphere comparison figure of ₂5% as.  “based on starting carbon in the form of methane”.  and.  “taken from Schlesinger and Miller 1983”.  The neutral yields are on input nitrogen, so the two are not on the same basis.  A laboratory experiment that sparked 0.13 bar each of CO₂ and N₂ over 100 ml of water in a 3.1 L flask, with a Tesla-coil discharge for 48 h at 23 °C, adding calcium carbonate as a pH buffer and ascorbate before hydrolysis.  The authors argue that the low yields reported before came from oxidation of the products during hydrolysis, and that oxidation inhibitors raised the yield; Stanley Miller is a posthumous co-author.  The article uses it to show that a neutral atmosphere does make amino acids once the acid is buffered and the products are protected from oxidation. ↩ ↩ ↩

1. 1a.

   From the introduction:  “The perceived problems in the synthesis of organic compounds under neutral atmospheric conditions have also been represented by some as evidence against evolutionary approaches to the study of the origins of life (Wells 2000).”  The reference list gives it as Wells J (2000) Icons of evolution.  Regnery, Washington DC, p 338.  Wells is cited a second time in the body, alongside Zohner and Broda 1979, for the observation that sparking N₂ and H₂O produces large amounts of HNO₂ and HNO₃. ↩ ↩

2. 1b.

   Table 2:  The yield in the O2 run, from Table 2, was 8 × 10^-5% without ascorbate and 2 × 10^-4% with it, against <10^-6% in the unsparked controls.  “To our surprise”. ↩ ↩

3. 1c.

   The contrast is with the reducing-atmosphere runs of Miller 1955, which the authors describe as producing.  “large amounts of polymeric material”. ↩

4. 1d.

   Table 2:  Yields of total amino acids on input N₂, hydrolysed without and with ascorbate:  unbuffered CO₂/N₂ 0.013% and 1.3%;  CO₂/N₂ with CaCO₃ 0.19% and 2.5%;  unsparked controls below 10^-6%.  Section Conclusions:  “Buffering the reaction solution with respect to pH and the addition of oxidation inhibitors such as ascorbic acid or Fe²⁺ prior to hydrolysis results in the recovery of up to several hundred times more amino acids than reported previously.” ↩

5. 1e.

   Section Results and Discussion:  “The main amino acids produced in these experiments were serine, glutamic acid, glycine and alanine, along with traces of aspartic acid, α-aminoisobutyric acid, γ-aminobutyric acid and β-alanine”.  “Few amino acids are detected before acid hydrolysis, and the amounts of free cyanide, aldehydes and ammonia were low, suggesting that the intermediates may be bound as nitriles or other precursors.”  “Under natural oceanic conditions with the pH near neutral, hydrolysis of the precursors would likely proceed slowly, but nevertheless take place over reasonably short geologic time scales.”  Table 1:  The HCN yield on input N₂ was 0.26% in the unbuffered run and 0.0% in the run buffered with CaCO₃. ↩

6. 1f.

   Section Introduction:  “Previous reports on the yields of amino acids in electric discharge experiments with N₂ + CO₂ were low but not zero (Schlesinger and Miller (1983)).  The small amount of amino acids formed under neutral conditions prompted our reinvestigation of these results in order to better constrain the amounts and types of amino acids that could be produced.” ↩

Criado-Reyes, Joaquín et al.  “The role of borosilicate glass in Miller-Urey experiment.”  Scientific Reports 11:21009.  2021.  On what formed only with glass:  “amino acids 6–7, 12–13, and 17, and the dipeptide 22, formed exclusively in the presence of borosilicate”.  Compounds 6, 7, 12, 13 and 17 are alanine, valine, aspartic acid, glutamic acid and isovaline, and 22 is glycylglycine.  “borosilicate systems afforded the complete set of nucleobases 36–40, while only 36, 39, and 40 were detected in the Teflon flask.”  The seventeen tentatively assigned amino acids across the study include glycine, alanine, valine, leucine, proline, serine, asparagine, aspartic acid, glutamic acid, lysine and histidine.  On mechanism:  “The silanol groups on the surface of the glass, and traces of metal that could be released by dissolution under the alkaline conditions of the experiment may contribute to the observed reactivity.”  A laboratory study of six spark-discharge runs at room temperature in CH₄ (200 mbar), NH₃ (200 mbar) and N₂ (100 mbar), in a borosilicate glass flask, a Teflon flask, and a Teflon flask with glass pieces in the water, each buffered at pH 8.7 or unbuffered at about pH 11.  The authors found that the glass gave a larger and more varied set of products, with some amino acids and a dipeptide forming only in the glass, and they suggest silanol groups on the glass surface may explain it.  The article uses it to show that the apparatus was doing chemistry that nobody accounted for. ↩ ↩ ↩

1. 2a.

   Table 1:  Row 7, "Total amount," in µg of product per 1.0 mg of crude.  Buffered runs (columns BSRB, TFRB, TFBSR/B): 393.82 borosilicate, 118.28 Teflon, 239.41 Teflon with borosilicate chips.  Unbuffered runs (columns BSR, TFR, TFBSR): 403.57, 246, 375.14.  Amino acids specifically, buffered: 159.45, 27.1, 60.53.  Both halves belong in any honest use of this table.  The intermediate value for Teflon-plus-chips is the real signal, but the effect is a factor of 3.3 in the buffered runs and only 1.6 in the unbuffered ones, so the headline comparison is condition-dependent.  The compound-count result (48 versus 31) is from Tables S2-S3 and is quoted in the body from the paper's own sentence. ↩ ↩

2. 2b.

   “Miller recreated in his experiments the atmosphere and waters of the primitive Earth.  The role of the rocks was hidden in the walls of the reactors.”  This is the paper's closing sentence.  Earlier in the discussion it says:  “The famous Miller-Urey synthesis triggered by sparking would be highly efficient at any place of the universe, provided a mineral surface is available.”  Note what the closing sentence does not say.  It does not say Miller's result was an artefact; it says the silicate chemistry was uncontrolled and unrecognised.  Both sides of this dispute have quoted the first half of that without the second. ↩ ↩

Trail, Dustin et al.  “The oxidation state of Hadean magmas and implications for early Earth's atmosphere.”  Nature 480:79–82.  2011.  Section Abstract:  “Reduced melts having oxygen fugacities close to that defined by the iron-wüstite buffer would yield volatile species such as CH₄, H₂, H₂S, NH₃ and CO, whereas melts close to the fayalite-magnetite-quartz buffer would be similar to present-day conditions and would be dominated by H₂O, CO₂, SO₂ and N₂ (refs 1-4)… Moreover, selected Hadean zircons (having chemical characteristics consistent with crystallization specifically from mantle-derived melts) suggest oxygen fugacities similar to those of Archaean and present-day mantle-derived lavas as early as ∼4,350 Myr before present.”  A Nature paper that reads the oxidation state of Hadean magmas from cerium in zircons.  It contrasts melts near the iron-wüstite buffer, which would give volatile gases such as methane, hydrogen and ammonia, with melts near the fayalite-magnetite-quartz buffer, which would be similar to present-day conditions and dominated by water, carbon dioxide, sulfur dioxide and nitrogen.  The article uses it to show that Hadean magmas were about as oxidised as modern ones, so volcanic outgassing would not have made the reducing mixture of the Miller experiment. ↩ ↩ ↩

Houchin, K. et al.  “Oxidized Hadean magmas and Archean mobile-lid tectonics revealed by Jack Hills zircon.”  Proceedings of the National Academy of Sciences 123:e2525466123.  Mar 2, 2026.  Section Abstract:  “Igneous cores record consistent, moderately oxidized magma conditions (FMQ-1 to +1), challenging notions of a highly reduced early Earth and supporting models that evoke efficient mantle convection throughout the Hadean… These findings imply Earth's mantle had near-modern redox states by 4.15 Ga.”  A 2026 study of Jack Hills zircons that reads the oxidation state of Hadean magmas.  The paper's main subject is the onset of mobile-lid tectonics; the redox result is the part the article cites, as a second method on the same zircons that agreed with the 2011 cerium study. ↩ ↩

Wells, Jonathan.  Icons of Evolution: Science or Myth? Why Much of What We Teach About Evolution Is Wrong.  Regnery.  2000.  A book by the biologist Jonathan Wells, a Discovery Institute fellow, arguing that ten standard textbook illustrations of evolution misstate the evidence.  Chapter 2 treats the Miller-Urey experiment:  it argues that the early atmosphere held some oxygen, that neutral gas mixtures yield no amino acids, and that textbooks present the experiment misleadingly.  The article uses it as the Intelligent Design statement of the atmosphere objection that Cleaves and colleagues answered.

1. 5a.

   Page 21:  “So what?  Maybe a water vapor-carbon dioxide-nitrogen atmosphere would still support a Miller-Urey-type synthesis (as long as oxygen is excluded).  But Fox and Dose reported in 1977 that no amino acids are produced by sparking such a mixture”.  Page 22:  “According to Holland, mixtures of carbon dioxide, nitrogen, and water yielded no amino acids at all.”  “The conclusion is clear:  if the Miller-Urey experiment is repeated using a realistic simulation of the Earth's primitive atmosphere, it doesn't work.” ↩ ↩

2. 5b.

   Page 25:  “The 2000 edition of Kenneth Miller and Joseph Levine's Biology a popular high school textbook, includes a drawing of the Miller-Urey apparatus with the caption:  "By re-creating the early atmosphere (ammonia, water, hydrogen and methane) and passing an electric spark (lightning) through the mixture, Miller and Urey proved that organic matter such as amino acids could have formed spontaneously."”  The caption is quoted as Wells gives it;  the textbook itself was not checked for this article. ↩

3. 5c.

   Page 17:  “The issue was never resolved.”  “Evidence from ancient rocks has been inconclusive.”  Page 18:  “James C. G. Walker likewise wrote that "the strongest evidence" for the composition of the primitive atmosphere "is provided by conditions for the origin of life.  A reducing atmosphere is required."”  “Dogma had taken the place of empirical science.”  Page 19:  “Smithsonian Institution paleobiologist Kenneth Towe (now emeritus) reviewed the evidence in 1996, and concluded that "the early Earth very likely had an atmosphere that contained free oxygen."” ↩ ↩

Johnson, Adam P. et al.  “The Miller Volcanic Spark Discharge Experiment.”  Science 322:404.  2008.  “We were interested in the second apparatus because it possibly simulates the spark discharge synthesis by lightning in a steam-rich volcanic eruption (6) (Fig. 1A).”  “We reanalyzed 11 vials in order to characterize the diversity of products synthesized in this apparatus.”  “The yield of amino acids synthesized in the volcanic experiment is comparable to, and in some cases exceeds, those found in the experiments Miller conducted (1, 3, 5).”  Fig. 1B caption:  “Gas quantities added were 200 torr of CH₄, 200 torr of NH₃, and 100 torr of H₂.”  Supporting material:  “Amino acids with chiral centers were racemic within the precision of the measurements.”  “We were not able to calculate actual yields for each experiment because there was no record of how much of the water from various experiments was saved.  However, Miller (S2, S3) gave the yields of glycine (based on carbon added as methane) from the three apparatus as 2.1 %, 1.8 %, and 0.4 %, respectively.”  A reanalysis of eleven vials of dried residue from Miller's 1953–54 experiments, from the second of his three apparatus, which injected a jet of steam and gas into a spark to imitate lightning in a volcanic eruption.  The authors identified 22 amino acids and five amines in it, several of them not reported before in Miller's work.  The article uses it for the diversity of products and for the caveat that the absolute yields cannot be recovered. ↩ ↩ ↩ ↩

1. 6a.

   The passage continues:  “Reduced gases and lightning associated with volcanic eruptions in hot spots or island arc–type systems could have been prevalent on the early Earth before extensive continents formed (8).” ↩ ↩

2. 6b.

   Page 404, figure 1:  “(B) The volcanic spark discharge apparatus used by Miller (3).  Gas quantities added were 200 torr of CH4, 200 torr of NH3, and 100 torr of H2”. ↩

Bergman, Jerry.  “Why the Miller–Urey research argues against abiogenesis.”  Journal of Creation 18(2):28–36.  Aug 2004.  Retrieved Aug 2, 2026.  Section Was there a methane-ammonia atmosphere?:  “The problem was stated as follows:  '… the accepted picture of the earth's early atmosphere has changed:  It was probably O₂-rich with some nitrogen, a less reactive mixture than Miller's, or it might have been composed largely of carbon dioxide, which would greatly deter the development of organic compounds.'”  The inner sentence is quoted by Bergman and adopted, not composed by him.  Reconstructing his footnote numbering against his reference list traces it to Charles Flowers, A Science Odyssey: 100 Years of Discovery (William Morrow, 1998), p. 173, a companion book to a PBS television series.  Bergman's internal cross-references are inconsistent (his list has "Lahav, ref. 21" when Lahav is item 26), so the numbering is not fully reliable and the attribution is not certain; every candidate source in that stretch of his list is popular-level and none is a geochemistry paper.  Whether Bergman transcribed Flowers correctly is not known.  A creationist review of the Miller–Urey experiments, reprinted by Answers in Genesis, which argues that the work counts against abiogenesis.  It reviews problems with the research and reports no new experiments.  The article uses it as the most-cited creationist treatment of the atmosphere question. ↩ ↩

1. 7a.

   “Most researchers also now believe that some O₂ was present on the early earth because it contained much water vapour, and photodissociation of water in the upper layers of the atmosphere produces oxygen.  Another reason is that large amounts of oxidized materials exist in the Precambrian geological strata.”  The two footnotes on that sentence are Scherer, S., "Could life have arisen in the primitive atmosphere?" Journal of Molecular Evolution 22 (1985): 91-94, and Thaxton, Bradley and Olsen, The Mystery of Life's Origin (1984), ch. 5. ↩

Catling, David C., and Kevin J. Zahnle.  “The Archean atmosphere.”  Science Advances 6:eaax1420.  2020.  Section INTRODUCTION: BACKGROUND TO ARCHEAN EARTH:  Their definition of the regime:  “Here, 'weakly reducing' means minor levels of reducing gases, such as CO, H₂, and CH₄, in an anoxic atmosphere of bulk oxidized gases, CO₂ and N₂.”  Section A BRIEF OVERVIEW OF THE ENVIRONMENT BEFORE THE ARCHEAN:  “the Hadean atmosphere and mantle were probably initially highly reducing, before subsequent oxidation either by hydrogen escape (29) or disproportionation of mantle FeO accompanied by Fe loss to the core (30, 31).  In any case, iron-cored impactors would reduce seawater to hydrogen and create transient, highly reducing atmospheres that may have been important for the origin of life (32, 33).”  “In summary, at the end of the Hadean, Earth had oceans, continents (16), an anoxic atmosphere likely rich in CO₂ and N₂, and probably life (Fig. 1).”  A review of the Archean atmosphere, the eon from 4 to 2.5 billion years ago, which combines new geological proxies with models; David Catling is at the University of Washington and Kevin Zahnle at NASA Ames Research Center.  The article uses it for the measured ceiling on Archean oxygen and for the picture of the Hadean atmosphere as anoxic and rich in carbon dioxide and nitrogen. ↩

1. 8a.

   Section Abstract:  “New geological proxies combined with models constrain atmospheric composition.  They imply surface O₂ levels <10^-6 times present, N₂ levels that were similar to today or possibly a few times lower, and CO₂ and CH₄ levels ranging ₂ to 2500 and 10² to 10⁴ times modern amounts, respectively.”  Section Negligible Archean O2 but oxygen oases after oxygenic photosynthesis evolved:  “The strongest constraint on Archean atmospheric composition is that the ground-level mixing ratio of O₂ was <10^-6 PAL (present atmospheric level) or <0.2–parts per million by volume (ppmv) O₂ for air of 1 bar, indicated by the presence of sulfur isotope MIF (S-MIF) in Archean sedimentary minerals.” ↩ ↩ ↩

2. 8b.

   Section Negligible Archean O2 but oxygen oases after oxygenic photosynthesis evolved:  “The strongest constraint on Archean atmospheric composition is that the ground-level mixing ratio of O₂ was <10^-6 PAL (present atmospheric level) or <0.2–parts per million by volume (ppmv) O₂ for air of 1 bar, indicated by the presence of sulfur isotope MIF (S-MIF) in Archean sedimentary minerals (Fig. 2A) (44, 47).”  Section References:  “47. J. Farquhar, H. Bao, M. Thiemens, Atmospheric influence of Earth's earliest sulfur cycle. Science 289, 756–758 (2000).” ↩

Sarfati, Jonathan.  “The Miller–Urey experiment revisited.”  Creation Ministries International.  Aug 13, 2024.  Section Standfirst:  “Miller--Urey experiment is still inadequate, and the early earth atmosphere was oxidizing.”  Section Dr Jonathan Sarfati responds:  The reader, Aleksey K. of Ukraine, asked whether the argument from the few amino acids found "shouldn't" be used now that "Jeffrey Bada in 2008, found 23 different amino acids."  Sarfati replied:  “We were long aware of this re-analysis, and remain singularly unimpressed.”  “Studying Table 2 in this paper showed that the 23 amino acids are not all relevant, since most life uses only 20.  The detected amino acids include β-alanine, α-aminoisobutyric acid, the α-, β-, and γ-aminobutyric acid isomers, isoserine, ethionine, which are not found in proteins.  And they failed to detect the proteinaceous amino acids phenylalanine, proline, histidine, tyrosine, lysine, asparagine, arginine, or glutamine.”  “(and this ignores the unjustifiable investigator interference of a trap to isolate the products before the energy source can destroy them).”  “So in conclusion, I think that the argument in the EAH film is still sound.”  EAH is CMI's film Evolution's Achilles' Heels.  A feedback article by Jonathan Sarfati, first published as a reply to a reader on 15 March 2015 and updated on 13 August 2024.  It argues that the Miller–Urey experiment is still inadequate, that the early atmosphere was oxidizing, and that the 23 amino acids reported in a 2008 reanalysis are not all relevant.  The article cites it for its standfirst and reply, for a fair point about the amino acids, and for an atmosphere claim that reads a zircon result as evidence for free oxygen. ↩ ↩ ↩ ↩

1. 9a.

   Section Box "Was earth's atmosphere really reducing as Miller and Urey thought?":  “Our current 'oxidizing' atmosphere would be hopeless, because oxygen would destroy the so-called building blocks, and indeed prevent their formation in the first place.”  “Also, the methane-ammonia atmosphere has largely been discarded, and there is much evidence that oxygen existed from a very early time, even according to evolutionary 'dating'.  A final blow was dealt late last year.  Scientists in the New York Center for Astrobiology at Rensselaer Polytechnic Institute analyzed what they called the oldest minerals on Earth:  zircons, 'dated' at 4.35 billion years old.  These contain a rare-earth metal called cerium.  The more oxidizing, the more cerium will be found in the highly oxidized form (Ce⁴⁺), and less at the more reduced form (Ce³⁺).  The conclusion?  A report said, 'The calibrations reveal an atmosphere with an oxidation state closer to present-day conditions.'  Thus Earth was never good for chemical evolution.  But since the researchers were unwilling to abandon their dogma, they resorted to the desperate measure of panspermia:  the building blocks came from outer space.”  The two references on that passage are Trail et al. 2011 (DOI 10.1038/nature10655) and "Setting the stage for life:  Scientists make key discovery about the atmosphere of early earth, sciencedaily.com, 30 November 2011."  The quoted sentence is attributed by Sarfati to the report, not to the paper.  Trail's abstract addresses magma oxygen fugacity and volcanic outgassing and does not mention panspermia. ↩

Miller, Stanley L., and Harold C. Urey.  “Organic Compound Synthesis on the Primitive Earth.”  Science 130(3370):245–251.  1959.  Page 248:  Referring to the fuller analysis published as Miller 1955:  “The compounds in the table account for 15 percent of the carbon added as methane, with the yield of glycine alone being 2.1 percent.”  Table 2:  Yields in units of 10^-5 moles from 710 mg of carbon added as CH₄: formic acid 233, glycine 63, glycolic acid 56, alanine 34, lactic acid 31, β-alanine 15, iminodiacetic acid 5.5, α-amino-n-butyric acid 5, sarcosine 5, α-hydroxybutyric acid 5, succinic acid 4, iminoacetic-propionic acid 1.5, N-methylalanine 1, glutamic acid 0.6, aspartic acid 0.4, α-aminoisobutyric acid 0.1.  A review article by Miller and Harold Urey that argues the early atmosphere was reducing, that hydrogen escaped from it over time, and that sparking experiments made organic compounds in such a mixture.  The often-quoted corollary that the other 85% of the carbon went into an uncharacterised polymeric residue is not stated in this paper, which says only that the tabulated compounds account for 15% of the carbon.  The article uses it for that 15 percent figure and for the Table 2 yields, which show that the simplest amino acid is the largest product and that the two acidic amino acids used in proteins are far down the list. ↩ ↩

Wollrab, Eva et al.  “Chemical Analysis of a 'Miller-Type' Complex Prebiotic Broth. Part I: Chemical Diversity, Oxygen and Nitrogen Based Polymers.”  Origins of Life and Evolution of Biospheres 46:149–169.  2016.  Section Abstract:  “Contrary to expectations, we cannot identify any preferred reaction product.”  “The capacity to spontaneously produce this extremely high degree of molecular variety in a very simple experiment is a remarkable feature of organic chemistry and possibly prerequisite for Life to emerge. It remains a future task to uncover how dedicated, organized chemical reaction pathways may have arisen from this degree of complexity.”  Section Results:  The instrument was tuned to m/z 150-300.  “In the mass spectra from the ESI+ and ESI- measurements we identified 668 substances (Fig. 4, Supplementary Table 1).”  Section Discussion:  “The experiment produced thousands of molecules from a broad mass range.”  “As far as we can say from our global approach, these species are not mere side products of a few preferred products. Rather many different species appear with equally important concentrations.”  A mass-spectrometry and NMR study of a simple Miller-type mixture of methane, ammonia and hydrogen at 2:2:1, run for five days.  The authors found many different substances and could not single out a preferred product, which they read as a remarkable sign of molecular variety.  The article cites it to show that the experiment makes many products in comparable amounts, not a few preferred ones. ↩ ↩

Meyer, Stephen C.  Signature in the Cell: DNA and the Evidence for Intelligent Design.  HarperOne.  2009.  A book-length case for intelligent design from the information in DNA, by Stephen Meyer, director of the Discovery Institute's Center for Science and Culture.  The article uses it for the design side's own view of Miller-Urey, which sets the atmosphere aside and rests on the tar and on the role of the experimenter.

1. 12a.

   Page 334:  “Nevertheless, after geochemical evidence established that the early earth probably did not have the reducing atmosphere that Miller first assumed, the relevance of his and many subsequent experiments came into question.”  “Assume for the moment that the reducing gases used by Stanley Miller did actually simulate the conditions on the early earth.  Would his experimental results establish the plausibility of an undirected process of chemical evolution?  Not necessarily.  Prebiotic simulation experiments invariably generate biologically irrelevant substances as well as desirable building blocks such as nucleotide bases, sugars, and amino acids.  But without investigator intervention, these undesirable by-products react with desirable building blocks to form inert compounds, such as a tar called melanoidin, the curse of the prebiotic chemist.” ↩ ↩

Wogan, Nicholas F. et al.  “Origin-of-life Molecules in the Atmosphere after Big Impacts on the Early Earth.”  The Planetary Science Journal 4:169.  2023.  Section Abstract:  “The minimum impactor mass that creates atmospheric CH₄/CO₂ > 0.1 is 4 × 10²⁰–5 × 10²¹ kg (570–1330 km diameter)… Atmospheres with copious nitriles have >360 K surface temperatures, perhaps posing a challenge for RNA longevity, although cloud albedo can produce cooler climates.”  Section 4.3:  “Our optimistic model, which considers the effect of nickel-catalyzed methane production, requires a >4 × 10²⁰ kg (>570 km) impactor (Figure 9).  The lunar cratering record and abundance of highly siderophile elements in Earth's mantle imply that between four and seven such impacts occurred during the Hadean (Marchi et al. 2014; Zahnle et al. 2020).  Our least optimistic model needs a >5 × 10²¹ kg (>1330 km) impact… The Hadean only experienced zero to two collisions this large.”  A modelling study of the atmosphere left after a large asteroid impact, using time-dependent computer models of its chemistry and climate.  It finds that an impact can leave a hydrogen and methane atmosphere that makes hydrogen cyanide, provided the impactor is large, and that such hot atmospheres may be too warm for RNA.  The article cites it for that price, and for the authors' proposal that the cyanide could be stored and used once the climate cooled.  Mirror:  arXiv ↩

1. 13a.

   Section 4.2:  “Additionally, while nitriles are produced in postimpact atmospheres, water bodies on land would likely be too warm for prebiotic chemistry… Nickel catalysts permit big HCN and HCCCN production for surface temperatures as small as ∼360 K (Figure 9).  Nucleotide building blocks are fragile at such hot temperatures, and conditions may not be conducive to an RNA world (Bada & Lazcano 2002).”  The stockpiling proposal:  “We propose that cyanides produced in hot postimpact atmospheres may instead be preserved, stockpiled, and concentrated and used in prebiotic schemes at a later time, when the climate is colder… For example, if HCN rains out at 10⁹ molecules cm^-2 s^-1 over 1 million yr (Figure 7), then ∼1.4 g cm^-2 HCN could be stockpiled, assuming that all molecules are preserved.”  The authors add that the ferrocyanide-stockpiling calculations they rely on.  “were at 273 and 298 K, which are far colder environments than the >360 K surface temperatures that coincide with large HCN production.” ↩ ↩

2. 13b.

   Section Abstract:  “However, geochemical evidence suggests that Hadean air was relatively oxidizing with negligible photochemical production of prebiotic molecules.”  “Smaller CH₄/CO₂ ratios produce HCN rainout rates of <10⁵ molecules cm⁻² s⁻¹ and negligible HCCCN.”  Page 8:  “Assuming the same lightning dissipation rate as modern Earth's, we find that lightning produces up to ∼10⁴ HCN molecules cm⁻² s⁻¹.  This value is small compared to the 10⁷–10⁹ HCN molecules cm⁻² s⁻¹ produced from photochemistry”.  Page 10:  “For a warm 373 K pond, Henry's law predicts that the dissolved HCN concentration is 4 × 10⁻¹¹ mol L⁻¹.”  Page 11:  “Yet ∼0.01 mol L⁻¹ HCN is required for polymerization (Sanchez et al. 1967), and published prebiotic schemes can use 1 mol L⁻¹ HCN (Patel et al. 2015).”  The pond figure is for the best case, an atmosphere made reducing by a giant impact, with HCN surface pressures up to 10^-9 bar. ↩ ↩ ↩ ↩

3. 13c.

   Page 10:  “Therefore, we argue that a hypothesized volcanic source of HCN and HCCCN requires further modeling and experiments before it can be compared to a photochemical source but, in general, seems challenging.” ↩

Calculated for this article (research/dilution.ts).  Stribling and Miller's example cyanide supply, 100 nmol per cm² per year, is 1.9 × 10⁹ molecules per cm² per second.³⁰  Wogan and colleagues give under 10⁵ for a Hadean atmosphere with CH₄/CO₂ below 0.1, a ratio of under 5.2 × 10^-5.¹³  Assuming the steady-state amino-acid level is supply times a fixed lifetime divided by ocean volume, so that it scales with supply, Miller's 3 × 10^-4 M becomes under 1.6 × 10^-8 M.  The assumption is ours, and the abstract does not say that its 3 × 10^-4 M uses the same example rate.  A second bound needs no lifetime:  lightning HCN at Wogan's upper value for post-impact air, 10⁴ molecules per cm² per second over the whole Earth, is 2.7 × 10⁶ mol a year, and 100 million years of it with no losses in the modern ocean's 1.3 × 10²¹ litres is 2 × 10^-7 M, about fifty thousand times below the 10^-2 M at which HCN polymerizes. ↩ ↩

Moldogazieva, Nurbubu T. et al.  “Redox chemistry of early Earth and the origin of life.”  Communications Chemistry 9:143.  2026.  Section Abstract:  “This review explores evidences that reconcile the dominant theories, including that: (i) the Hadean atmosphere was weakly oxidizing, but transiently reducing, (ii) hydrothermal systems provided energy for organic synthesis supporting both heterotrophs and chemoautotrophs, (iii) organic compounds were transported between different environments, and (iv) life emerged in multiple local environments.”  A review of the chemistry of early Earth and of how the first molecules of life could have formed, which argues that the dominant theories can be reconciled.  Its abstract says the Hadean atmosphere was weakly oxidizing but transiently reducing.  The article uses it because it is the field's most recent review, and it describes the early atmosphere in just that way. ↩ ↩

Miller, Stanley L.  “A Production of Amino Acids Under Possible Primitive Earth Conditions.”  Science 117(3046):528–529.  1953.  Page 528:  “The experimental procedure was to seal off the opening in the boiling flask after adding 200 ml of water, evacuate the air, add 10 cm pressure of H₂, 20 cm of CH₄, and 20 cm of NH₃. The water in the flask was boiled, and the discharge was run continuously for a week.”  A two-page report of a laboratory experiment in which Miller sealed water, methane, ammonia and hydrogen in a flask, ran an electric spark through the mixture for a week, and tested the residue for amino acids by paper chromatography, a method that separates molecules along a strip of paper.  He identified glycine and two forms of alanine with confidence, and two more less surely, in a total yield in the milligram range.  The article uses it for the exact gas mixture, for what the experiment found, and for Miller's own statement that he meant to copy an early atmosphere, not to get the best yield. ↩

1. 16a.

   Page 529:  “The spots marked A and B are unidentified as yet, but may be beta and gamma amino acids. These are the main amino acids present, and others are undoubtedly present but in smaller amounts. It is estimated that the total yield of amino acids was in the milligram range.” ↩

2. 16b.

   Page 528:  “During the run the water in the flask became noticeably pink after the first day, and by the end of the week the solution was deep red and turbid. Most of the turbidity was due to colloidal silica from the glass. The red color is due to organic compounds adsorbed on the silica.” ↩

3. 16c.

   Page 529:  “In this apparatus an attempt was made to duplicate a primitive atmosphere of the earth, and not to obtain the optimum conditions for the formation of amino acids.” ↩ ↩

Parker, Eric T. et al.  “Primordial synthesis of amines and amino acids in a 1958 Miller H₂S-rich spark discharge experiment.”  Proceedings of the National Academy of Sciences 108:5526–5531.  2011.  Section Abstract:  “A total of 23 amino acids and 4 amines, including 7 organosulfur compounds, were detected in these samples. The major amino acids with chiral centers are racemic within the accuracy of the measurements, indicating that they are not contaminants introduced during sample storage. This experiment marks the first synthesis of sulfur amino acids from spark discharge experiments designed to imitate primordial environments.”  The gas mixture:  “produced via spark discharge using a gaseous mixture of H₂S, CH₄, NH₃, and CO₂.”  Page 5526:  Their statement of the field:  “Many geoscientists today favor an early atmosphere that was likely weakly reducing, containing N₂, CO₂ (5), H₂O, CO and lesser amounts of more reduced species such as H₂S, CH₄, and H₂ (6). However, reducing conditions may have been prevalent on the Earth locally or transiently; for example, in the vicinity of volcanic plumes.”  A reanalysis of residues from a 1958 spark experiment that Stanley Miller ran with hydrogen sulfide added, and which had apparently never been analysed or reported.  The team used modern liquid chromatography and mass spectrometry to find 23 amino acids and 4 amines, including the first sulfur amino acids from a spark experiment designed to imitate early Earth.  The article uses it for the sulfur mixture and for the racemic result, which shows that the amino acids were not contaminants picked up in storage. ↩

1. 17a.

   Page 5527:  “However, aspartic and glutamic acids as well as serine, which are present in relatively low abundances, are enriched in the L-enantiomer, indicating that trace amounts of contamination of some amino acids may be present.” ↩

Gishlick, Alan D.  “Icon 1: The Miller-Urey Experiment.”  Icons of Evolution? Why much of what Jonathan Wells writes about evolution is wrong, National Center for Science Education.  2003.  Section Wells boils off:  “First, Wells's claim that researchers are ignoring the new atmospheric data, and that experiments like the Miller-Urey experiment fail when the atmospheric composition reflects current theories, is simply false.  The current literature shows that scientists working on the origin and early evolution of life are well aware of the current theories of the earth's early atmosphere and have found that the revisions have little effect on the results of various experiments in biochemical synthesis.”  The National Center for Science Education's chapter-by-chapter reply to Wells' Icons of Evolution, written by Alan Gishlick of the NCSE staff.  This chapter answers Wells on the Miller-Urey experiment and reviews how ten textbooks present it.  The article uses it as the published reply to Wells, right on oxygen and ahead of the evidence on neutral-atmosphere yields. ↩

1. 18a.

   Section Wells boils off:  “In truth, nearly all researchers who work on the early atmosphere hold that oxygen was essentially absent during the period in which life originated (Copley, 2001) and therefore oxygen could not have played a role in preventing chemical synthesis.” ↩

Cleaves, H. James.  “Prebiotic Chemistry: What We Know, What We Don't.”  Evolution: Education and Outreach 5:342–360.  2012.  “Spark discharge experiments using CH₄, CO, or CO₂ as a carbon source with various amounts of H₂ show that methane is the best source of amino acids, but CO and CO₂ are almost as good if a high H₂/C ratio is used.  Without added H₂, amino acid yields are quite low, especially when CO₂ is the sole carbon source (Stribling and Miller 1987).  Recent results, however, suggest that amino acid yields from neutral atmospheres may be higher than previously thought.”  On the Hadean hydrogen level he cites Miller and Orgel's estimate of 10^-4 to 10^-2 atm and says.  “it is unclear what would have governed this balance.”  A review of the synthesis of small organic compounds in prebiotic chemistry, by H. James Cleaves of the Blue Marble Space Institute of Science.  The article uses it for the author's own qualification that hydrogen still matters for synthesis from neutral gases. ↩

1. 19a.

   Page 347:  “In CH₄/N₂ atmospheres, HCN is produced abundantly (Chameides and Walker 1981; Stribling and Miller 1987), but in CO₂/N₂ atmospheres, most of the N atoms produced by splitting N₂ recombine with O atoms to form NOx species (Chameides and Walker 1981).”  Page 351:  “Assuming favorable HCN production rates, steady-state concentrations of HCN of 2×10^-6 molar at pH eight and zero degree Celsius in the primitive oceans have been estimated (Miyakawa et al. 2002b).  At 100 degrees Celsius and pH eight, this was estimated at 7×10^-13 molar.  Oligomerization and hydrolysis compete at approximately 10^-2 molar concentrations of HCN at pH nine (Sanchez et al. 1966a, b)”. ↩

2. 19b.

   Page 342, section Abstract:  “Regardless of their origin, organic compounds would need to be concentrated and complexified by environmental mechanisms.” ↩

Zahnle, Kevin J. et al.  “Creation and Evolution of Impact-generated Reduced Atmospheres of Early Earth.”  The Planetary Science Journal 1:11.  2020.  Section Abstract:  “The paradox can be resolved by exploiting the reducing power inherent in the 'late veneer,' i.e., material accreted by Earth after the Moon-forming impact… The major primary product of reaction between the late veneer's iron and Earth's water was H₂.  Ocean vaporizing impacts generate high pressures and long cooling times that favor CH₄ and NH₃.”  Section Discussion:  Their conclusions on the impacts:  “Each great impact left Earth in a state resembling somewhat the state of early Earth as sketched by Urey (1952) for periods that may have been less than a million years or as long as 100 million years, the duration depending on the size of the impact and on the flux of ultraviolet radiation from the young Sun.”  The authors also argue against themselves:  “A possible problem posed by the biggest impact is that, although it brings the most reducing power, it is also the most likely to leave the surface too hot to promote prebiotic evolution, and for a long time.  Even ignoring CO₂ and CH₄, the greenhouse effect provided by tens of bars of H₂ could raise the surface temperature to 400 K or more.”  A modelling study of the atmosphere left after large impacts on early Earth, by Kevin Zahnle and three colleagues.  It argues that iron from the impactor reacted with water to make hydrogen, and that impacts large enough to vaporise the oceans favoured methane and ammonia, so the early atmosphere was reduced for a time.  Such an atmosphere lasted from under a million years to as long as 100 million years, and the biggest impact may leave the surface too hot for a long time.  The article cites it as the mainstream answer to the paradox that life seems to need a reduced atmosphere, and as an answer with a price.  Mirror:  arXiv ↩

Paschek, Klaus et al.  “Deep Mantle-Atmosphere Coupling and Carbonaceous Bombardment: Options for Biomolecule Formation on an Oxidized Early Earth.”  arXiv.  Mar 19, 2025.  Section Abstract:  “If the Hadean atmosphere was initially oxidized and CO₂-rich (90 %), we find serpentinization alone can reduce the atmosphere, resulting in WLP concentrations of an order of magnitude lower than the reducing carbonaceous bombardment case.  In both cases, concentrations are sufficient for nucleotide synthesis, as shown in experimental studies.”  A modelling study, not a measurement, of where the reducing gases on Hadean Earth could have come from, including serpentinization and bombardment by carbonaceous meteorites, and of the molecules that would collect in warm little ponds (WLPs).  The preprint, arXiv:2503.15479, was accepted for the Astrophysical Journal.  The article cites it as one of two alternatives that need no impactor, for the claim that serpentinization alone can reduce the atmosphere enough for nucleotide synthesis. ↩

Diukarev, N. et al.  “The Origin of the Feedstock Molecules for Life on the Hadean Earth.”  Angewandte Chemie International Edition 64.  2025.  Section Abstract:  “The Hadean Earth was, however, surrounded by a CO₂-dominated atmosphere and the question of how under such inert conditions the biomolecules could have formed is unsolved.  Here, we report that HNO and formaldehyde, which form robustly in a weakly reducing atmosphere by lightning and UV-irradiation, react with SO₂ to produce oxime, amidoxime, and nitrile-containing molecules, which react to give precursors to amino acids and all four canonical nucleosides.”  A 2025 chemistry study from Thomas Carell's group in Munich.  It reports that HNO (nitroxyl) and formaldehyde, which form in a weakly reducing atmosphere by lightning and UV light, react with sulfur dioxide to give precursors of amino acids and all four canonical nucleosides.  The article cites it as one of two alternatives that need no impactor at all. ↩

Ohmoto, Hiroshi, and James G. Ferry.  “The hydrogen, methane and ammonia biosphere on early Earth.”  Scientific Reports 16:14017.  2026.  Section Discussion:  “the current paradigm for the origin and evolution of life from a CO₂–N₂-rich atmosphere is invalid.”  The paper's own text acknowledges.  “this interpretation contradicts the current paradigms of microbial evolution.”  A modelling study with no new rock data: the authors calculate the chemistry of the Hadean mantle, the magma-ocean atmosphere and hydrothermal fluids from thermodynamic equations.  They conclude that the early atmosphere was rich in methane, ammonia and hydrogen, which makes the Oparin–Urey–Miller model valid.  The article cites it as evidence that the question is still argued, without relying on it, because it runs against the zircon results. ↩

Sarfati, Jonathan.  “15 loopholes in the evolutionary theory of the origin of life: Summary.”  Creation Ministries International.  Feb 7, 2024.  Section Loophole 1:  “There is almost universal agreement among specialists that Earth's primordial atmosphere contained no methane, ammonia or hydrogen — 'reducing' gases.  Rather, most evolutionists now believe it contained carbon dioxide and nitrogen.  Miller-type sparking experiments will not work with those gases in the absence of reducing gases.  See The primitive atmosphere.  Even worse, such an atmosphere would have produced mostly carboxylic acids, which are chain terminators for polypeptides.”  “The atmosphere contained free oxygen, which would destroy organic compounds.  Oxygen would be produced by photodissociation of water vapour.  Oxidized minerals such as hematite are found as early as 3.8 billion years old, almost as old as the earliest rocks, and 300 million years older than the earliest life.  There is also evidence for organisms complex enough to photosynthesize at 3.7 billion years ago (Rosing, M.T. and Frei, R., U-rich Archaean sea-floor sediments from Greenland—indications of >3700 Ma oxygenic photosynthesis, Earth and Planetary Science Letters 217: 237–244, 2004).”  A web summary of fifteen objections to the idea that life arose by chemistry, written by Jonathan Sarfati, who holds a PhD in physical chemistry.  The page was first published in 2000.  The article uses it because its first objection opens with the atmosphere and then makes an oxygen claim that the article calls false. ↩ ↩

Jenewein, Christian et al.  “Concomitant formation of protocells and prebiotic compounds under a plausible early Earth atmosphere.”  Proceedings of the National Academy of Sciences 122(2):e2413816122.  2025.  From the body, the film.  “only forms in borosilicate reactors, which can be attributed to the catalytic role of silica in the synthesis of the HCN-polymers, most probably through its silanol groups.”  Section Significance:  “only in the presence of water, silica induces the formation of a solid organic film made of polymers of hydrogen cyanide”.  “nano- to micron-size biomorphic protocells”.  A laboratory study in which a spark discharge in a glass reactor made a solid organic film, with silica from the glass acting as its catalyst.  The film is made of hydrogen cyanide polymers, and the "protocells" in it are polymers precipitated at a water–gas interface, not lipid compartments.  The paper carries two 2025 corrections, both administrative: PNAS 122(9):e2500712122 corrects a production error in the author affiliations, and 122(14):e2505069122 adds a European Research Council funding acknowledgment; neither touches a number or a result.  The article uses it as a warning that cell-shaped structures can form without life. ↩

Meng, Yifan et al.  “Spraying of water microdroplets forms luminescence and causes chemical reactions in surrounding gas.”  Science Advances 11:eadt8979.  2025.  Section Abstract:  “Similar findings to the Urey-Miller experiment were observed by spraying room temperature water microdroplets into a gas mixture containing nitrogen, methane, carbon dioxide, and ammonia, which leads to the synthesis of organic molecules containing carbon-nitrogen (C─N) bonds.”  A laboratory study from Stanford in which spraying water made electrical sparks between the droplets with no external voltage, and the products detected were hydrogen cyanide, glycine, urea and uracil.  The gas mixture is still a reducing one, so the result does not touch the objection about the atmosphere, which is about its composition.  The article cites it against the objection that lightning was too rare to matter, because water sprays are common and lightning is not. ↩ ↩

Lazcano, Antonio, and Jeffrey L. Bada.  “The 1953 Stanley L. Miller Experiment: Fifty Years of Prebiotic Organic Chemistry.”  Origins of Life and Evolution of Biospheres 33:235–242.  2003.  Section 1. Introduction:  “One of the surprising results of this experiment was that the products were not a random mixture of organic compounds; rather, a relatively small number of compounds were produced in surprisingly high yields.”  “Moreover, with a few exceptions, the compounds were of biochemical significance, thus providing support for the primitive soup heterotrophic theory proposed in the 1920's by Oparin and Haldane.”  A historical account, written for the fiftieth anniversary of Miller's 1953 paper, of the events that led to its publication and of what the experiment showed.  The authors describe the products as mostly of biochemical significance.  The article uses it for Miller's own finding that a small number of compounds dominated the products, a result that rested on 1950s chromatography. ↩

Benner, Steven A.  “Paradoxes in the Origin of Life.”  Origins of Life and Evolution of Biospheres 44:339–343.  2014.  A conference essay, not an experiment, given at a 2014 meeting in Kyoto.  It argues that sixty years of prebiotic chemistry have produced tens of thousands of papers, each a success only by its own definition, and that the origin-of-life problem is still unsolved.  The author has run a prebiotic-chemistry laboratory for two decades and chaired the 2014 Gordon Research Conference on the origin of life, and the article uses his sceptical reading of Wollrab's result, in which an unconstrained reaction network runs toward asphalt and the more products there are, the less of any one.

1. 28a.

   Page 340:  “We are now 60 years into the modern era of prebiotic chemistry.  That era has produced tens of thousands of papers attempting to define processes by which 'molecules that look like biology' might arise from 'molecules that do not look like biology', find conditions where oligomers might form spontaneously from those molecules, identify constraints on pre-metabolic cycles that might deliver those molecules without leaking material into the complexity sometimes characterized as 'asphalt', or assemble ways to create chiral compounds largely free from their enantiomers.  For the most part, these papers report 'success' in the sense that those papers define the term.  ¶  And yet, the problem remains unsolved.”  Frequently miscited as Astrobiology 2014; it is not. ↩

Thaxton, Charles B. et al.  The Mystery of Life's Origin: Reassessing Current Theories.  Philosophical Library.  1984.  The first book-length critique of chemical-evolution research from the design side, by a chemist, a materials engineer and a geochemist.  Its middle chapters weigh the destruction and dilution of products on the early Earth and propose a scale of legitimate and illegitimate "investigator interference" in simulation experiments.  The article uses it as the original source of the trap and dilution objections.

1. 29a.

   Page 60:  “Dose arrives at an upper limit estimate of amino acid concentration in the primitive ocean of 10^-7 M, some 10,000 times more dilute than the optimistic estimates reported above.”  Page 61:  “Even so, the above estimates are sufficient to suggest that the primordial ocean would have been an extremely dilute "soup," much too dilute to reasonably expect the spontaneous formation of proteins.” ↩

2. 29b.

   Page 102:  “Traps function by continually removing the small fraction of product formed by the reactions.”  “Like the practice of concentrating chemical reactants, this technique is a legitimate means of collapsing time to manageable amounts.”  Page 103:  “In spite of these factors it is not at all clear that the ocean would have provided the shielding function of a trap.  Laboratory traps are not usually exposed to long-wavelength ultraviolet light, which would be the case for the ocean, where UV light would penetrate some tens of meters beneath the surface.  Furthermore, ocean currents periodically surface even the deep water”. ↩

Stribling, Roscoe, and Stanley L. Miller.  “Energy yields for hydrogen cyanide and formaldehyde syntheses: the HCN and amino acid concentrations in the primitive ocean.”  Origins of Life and Evolution of the Biosphere 17(3-4):261–273.  1987.  Section Abstract:  “From these production rates of HCN (e.g. 100 nmoles cm-2 yr-1) and the experimental hydrolysis rates, the steady state concentration in the primitive ocean can be calculated (e.g., 4 X 10(-6) M at pH 8 and 0 degrees).  A steady state amino acid concentration of 3 X 10(-4) M is estimated from the HCN production rate and the rate of decomposition of the amino acids by passage through the submarine vents.”  A laboratory study from Stanley Miller's group that sparked CH₄, CO or CO₂ with N₂, H₂O and varying H₂ at low energy to measure how much HCN and formaldehyde each unit of energy makes, then scaled the yields to the early Earth.  Methane mixtures gave the most HCN.  The article uses its ocean amino-acid estimate as the mainstream counterpart to the creationist dilution figure. ↩ ↩