Lightning in a Jar

The Mechanism

*Stanley Lloyd Miller* (born Oakland, California, 7 March 1930; died National City, California, 20 May 2007) was a graduate student in the chemistry department at the University of Chicago in 1952, looking for a dissertation topic. He had heard a talk in October 1951 by *Harold Clayton Urey* (born Walkerton, Indiana, 29 April 1893; died La Jolla, California, 5 January 1981) — the 1934 Nobel laureate in chemistry (for the discovery of deuterium) and one of the most influential American physical chemists of the 20th century — in which Urey had laid out the *Oparin-Haldane hypothesis*: that the atmosphere of the early Earth, before the emergence of life, would have been *reducing* (rich in hydrogen, methane, ammonia, water vapor; poor in molecular oxygen), and that complex organic molecules might form spontaneously in such an atmosphere given a sufficient source of energy. The hypothesis was due originally to the Soviet biochemist *Aleksandr Ivanovich Oparin* (*The Origin of Life on Earth*, Russian 1924; revised English ed. 1936) and to the British geneticist *J.B.S. Haldane* (*The Origin of Life*, 1929). Urey was teaching the hypothesis to graduate seminars at Chicago in 1951 but had not himself attempted to test it. Miller, at the end of Urey's seminar, walked up afterward and asked whether he could attempt to *test the hypothesis experimentally* as a dissertation project. Urey said no. The experiment, Urey explained, was too risky to bet a PhD on: it might not work; if it did work, it might not produce identifiable products; if it did produce identifiable products, they might be so faint as to be impossible to characterize without months of analytical work. Urey suggested instead that Miller work on something more tractable — perhaps thallium and lead chemistry, his original assignment. Miller insisted. Urey eventually gave in, on the condition that if no results were obtained within a year, Miller would switch to a safer thesis topic. Miller, with a glassblower at the University of Chicago, designed and built the apparatus in early 1953. It consisted of two connected sealed glass flasks. The lower (5-litre) flask contained boiling liquid water. The upper (2-litre) flask contained the *putative prebiotic atmosphere*: methane (CH₄), ammonia (NH₃), molecular hydrogen (H₂), and water vapor in a 2:2:1 ratio with water vapor saturating, at approximately atmospheric pressure. The two flasks were connected by glass tubes in a closed circuit so that water vapor from the boiling-water flask circulated continuously into the upper "atmosphere" flask and out again through a condenser back down to the water flask. In the upper flask, *two tungsten electrodes* were sealed through the glass and connected to a 60,000-volt transformer that produced a continuous spark discharge across the gases — a laboratory simulation of *lightning* in the prebiotic atmosphere. The condensed water from the upper flask, before returning to the lower flask, passed through a small *U-shaped trap* designed to collect any non-volatile products that might form. The apparatus was assembled in February 1953. The boiling water was started. The spark was switched on. Within hours the gas in the upper flask had turned pink. Within a day the trap at the bottom was visibly yellowish. Within a week the solution in the trap was dark yellow, almost brown. Miller drained the trap, ran the contents through a paper chromatography column to separate any organic compounds present, sprayed the developed chromatogram with ninhydrin (a reagent that turns purple in the presence of amino acids), and saw five distinct purple spots. He identified them: *glycine*, *α-alanine*, *β-alanine*, *aspartic acid*, and *α-aminobutyric acid*. The simplest amino acids — the building blocks of proteins — had been synthesized abiotically from the gases of a prebiotic atmosphere, in a flask, in less than a week, by a 23-year-old graduate student in his first attempt. Miller submitted a single short paper to *Science* in February 1953. The journal sent the paper to Urey for review (Urey, as Miller's advisor, was at first listed as a co-author; Urey *removed his own name* from the paper before submission, telling Miller that if the paper became famous, having Urey's name on it would let people credit Urey for the work rather than the student who had done it). The paper, "A Production of Amino Acids Under Possible Primitive Earth Conditions," *Science* 117(3046): 528-529, was published on 15 May 1953, by Stanley L. Miller, sole author. The result was immediately recognized as one of the most important experimental results of the century. The next year Miller published a full follow-up paper (*Journal of the American Chemical Society* 77: 2351-2361, 1955) characterizing additional products. He completed his PhD at Chicago in 1954, moved through postdoctoral positions, and joined the faculty at the University of California, San Diego in 1960, where he spent the rest of his career studying prebiotic chemistry. The 1953 experiment became the foundational icon of *origin-of-life* research. It was reproduced in every introductory biology textbook, every general-chemistry textbook, every popular-science account of the origin of life, for the next 70 years. But the experiment had a hidden second half that nobody but Miller and his immediate students knew about. In 1953, after the original "spark + closed circuit" experiment, Miller had attempted *two variant designs* of the same basic apparatus. One variant — the *aspirator design* — used a partially evacuated upper flask with a jet of water vapor injected at high velocity through a thin nozzle to mimic *volcanic outgassing*; the spark discharge sat downstream of the water-vapor jet. The other variant introduced a *silent electrical discharge* instead of the spark. Miller ran both variants in 1953 with the same gas mixture, collected the products in identical traps, and put the *unanalyzed vials* on a shelf in his lab, intending to come back to them. He never did. He completed his PhD on the spark-discharge work, moved to UCSD, and the vials stayed on his shelf in San Diego for 55 years. In 1999 Miller suffered a serious stroke. He gave the contents of his laboratory to his former student *Jeffrey L. Bada* at the Scripps Institution of Oceanography in La Jolla. Among the inherited material were the labeled but unanalyzed glass vials from the 1953 aspirator-design and silent-discharge experiments. Bada took them as a historical curiosity but did not analyze them until 2007. Miller died in May 2007. In 2008, Bada and his postdoctoral team — Adam Johnson, Antonio Lazcano, H. James Cleaves, Jason Dworkin, Daniel Glavin — opened the 55-year-old vials and ran the contents through *modern HPLC* with mass spectrometry (analytical sensitivity roughly a million times better than the paper chromatography Miller had used in 1953). The aspirator-design vials — the "volcanic" variant Miller had viewed as a flop — contained *22 distinct amino acids* and 5 amines, including all five of Miller's original 1953 amino acids and 17 others, several of them previously assumed to require living biological synthesis. The silent-discharge vials contained a subset. The aspirator design — the experiment Miller had labeled and shelved in 1953 because it had been less productive *by the analytical methods of 1953* — had in fact been substantially *more* productive than the published spark-discharge design that became the icon of origin-of-life chemistry: the paper, A.P. Johnson, H.J. Cleaves, J.P. Dworkin, D.P. Glavin, A. Lazcano & J.L. Bada, "The Miller Volcanic Spark Discharge Experiment," *Science* 322: 404 (17 October 2008). Bada's team also re-analyzed Miller's original 1953 spark-discharge vials, which were also in the inherited collection. *Those* vials, with the same modern HPLC, were shown to contain not five amino acids but *more than twenty*. Miller in 1953, with paper chromatography, had detected the brightest five spots and missed everything below his detection threshold. The most-famous chemistry experiment of the 20th century, when looked at with modern instruments, was three times more productive than its 1953 publication had reported. The result is not a minor curiosity. It substantially strengthens the case that *prebiotic synthesis of the molecular building blocks of life is robust and easy* on any planet with liquid water, energy input, and a moderately reducing atmosphere. (Modern caveats: the *Earth's* early atmosphere was probably not as strongly reducing as Miller and Urey assumed in 1953 — current models favor an atmosphere dominated by CO₂, N₂, and H₂O with smaller amounts of H₂ and CH₄, less amenable to organic synthesis. The Miller-Urey experiment may not, in detail, describe what happened on Earth. But *local* environments rich in CH₄ and NH₃ — submarine hydrothermal vents, volcanic outgassing plumes, the immediate aftermath of large meteorite impacts — would have had Miller-Urey-like conditions, and the chemistry he demonstrated would have run there.) The vials are still in Bada's lab at Scripps. Most of them have not yet been analyzed. The most-famous chemistry experiment of the 20th century is, as of 2026, still being run — by the same shelf of glass vials, 73 years later, with the analytical instruments Miller did not have in 1953.