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Miller–Urey experiment


Miller–Urey experiment

The experiment

The Miller–Urey experiment[1] (or Miller experiment)[2] was a chemical abiogenesis, it was conducted in 1952[3] by Stanley Miller, under the supervision of Harold Urey, at the University of Chicago and later the University of California, San Diego and published the following year.[4][5][6]

After Miller's death in 2007, scientists examining sealed vials preserved from the original experiments were able to show that there were actually well over 20 different amino acids produced in Miller's original experiments. That is considerably more than what Miller originally reported, and more than the 20 that naturally occur in life.[7] There is abundant evidence of major volcanic eruptions 4 billion years ago, which would have released carbon dioxide (CO2), nitrogen (N2), hydrogen sulfide (H2S), and sulfur dioxide (SO2) into the atmosphere. Experiments using these gases in addition to the ones in the original Miller experiment have produced more diverse molecules.[8] Some evidence suggests that Earth's original atmosphere might have had a different composition from the gas used in the Miller experiment. But prebiotic experiments continue to produce simple to complex compounds under varying conditions.[9]


  • Experiment 1
  • Chemistry of experiment 2
  • Other experiments 3
  • Earth's early atmosphere 4
  • Extraterrestrial sources 5
  • Recent related studies 6
  • References 7
  • External links 8


Descriptive video of the experiment

The experiment used water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2). The chemicals were all sealed inside a sterile array of 5 litre glass flask connected to 500 ml flask half-full of liquid water. The liquid water in the smaller flask was heated to induce evaporation, and the water vapour was allowed to enter the bigger flask. Continuous electrical sparks were fired between the electrodes to simulate lightning in the water vapour and gaseous mixture, and then the simulated atmosphere was cooled again so that the water condensed and trickled into a U-shaped trap at the bottom of the apparatus.

After a day, the solution collected at the trap had turned pink in colour.[10] At the end of one weeks of continuous operation, the boiling flask was removed, and mercuric chloride was added to prevent microbial contamination. The reaction was stopped by adding barium hydroxide and sulfuric acid, and evaporated to remove impurities. Paper chromatography revealed the presence of glycine, α- and β-alanine. Miller could not ascertain aspartic acid and GABA, due to faint spots.[4]

In a 1996 interview, Stanley Miller recollected his lifelong experiments following his original work and stated: "Just turning on the spark in a basic pre-biotic experiment will yield 11 out of 20 amino acids."[11]

As observed in all subsequent experiments, both left-handed (L) and right-handed (D) optical isomers were created in a racemic mixture. In biological systems, most of the compounds are non-racemic, or homochiral.

The original experiment remains today under the care of Miller and Urey's former student Jeffrey Bada, a professor at UCSD, at the University of California, San Diego, Scripps Institution of Oceanography.[12] The apparatus used to conduct the experiment is on display at the Denver Museum of Nature and Science.[13]

Chemistry of experiment

One-step reactions among the mixture components can produce hydrogen cyanide (HCN), formaldehyde (CH2O),[14][15] and other active intermediate compounds (acetylene, cyanoacetylene, etc.):

CO2 → CO + [O] (atomic oxygen)
CH4 + 2[O] → CH2O + H2O
CO + NH3 → HCN + H2O
CH4 + NH3 → HCN + 3H2 (BMA process)

The formaldehyde, ammonia, and HCN then react by Strecker synthesis to form amino acids and other biomolecules:

CH2O + HCN + NH3 → NH2-CH2-CN + H2O
NH2-CH2-CN + 2H2O → NH3 + NH2-CH2-COOH (glycine)

Furthermore, water and formaldehyde can react, via Butlerov's reaction to produce various sugars like ribose.

The experiments showed that simple organic compounds of building blocks of proteins and other macromolecules can be formed from gases with the addition of energy.

Other experiments

This experiment inspired many others. In 1961, Joan Oró found that the nucleotide base adenine could be made from hydrogen cyanide (HCN) and ammonia in a water solution. His experiment produced a large amount of adenine, the molecules of which were formed from 5 molecules of HCN.[16] Also, many amino acids are formed from HCN and ammonia under these conditions.[17] Experiments conducted later showed that the other RNA and DNA nucleobases could be obtained through simulated prebiotic chemistry with a reducing atmosphere.[18]

There also had been similar electric discharge experiments related to the origin of life contemporaneous with Miller–Urey. An article in The New York Times (March 8, 1953:E9), titled "Looking Back Two Billion Years" describes the work of Wollman (William) M. MacNevin at The Ohio State University, before the Miller Science paper was published in May 1953. MacNevin was passing 100,000 volt sparks through methane and water vapor and produced "resinous solids" that were "too complex for analysis." The article describes other early earth experiments being done by MacNevin. It is not clear if he ever published any of these results in the primary scientific literature.[19]

K. A. Wilde submitted a paper to Science on December 15, 1952, before Miller submitted his paper to the same journal on February 14, 1953. Wilde's paper was published on July 10, 1953.[20] Wilde used voltages up to only 600 V on a binary mixture of

  • A simulation of the Miller–Urey Experiment along with a video Interview with Stanley Miller by Scott Ellis from CalSpace (UCSD)
  • Origin-Of-Life Chemistry Revisited: Reanalysis of famous spark-discharge experiments reveals a richer collection of amino acids were formed.
  • - Miller–Urey experiment explained.
  • - Miller experiment with Lego bricks.
  • Long-Neglected Experiment Gives New Clues to Origin of Life
  • Primordial synthesis of amines and amino acids in a 1958 Miller H2S-rich spark discharge experiment

External links

  1. ^ Hill HG, Nuth JA (2003). "The catalytic potential of cosmic dust: implications for prebiotic chemistry in the solar nebula and other protoplanetary systems". Astrobiology 3 (2): 291–304.  
  2. ^ Balm SP, Hare J.P., Kroto HW (1991). "The analysis of comet mass spectrometric data". Space Science Reviews 56: 185–9.  
  3. ^ Bada, Jeffrey L. (2000). "Stanley Miller's 70th Birthday" (PDF). Origins of Life and Evolution of the Biosphere (Netherlands: Kluwer Academic Publishers) 30: 107–12.  
  4. ^ a b Miller, Stanley L. (1953). "Production of Amino Acids Under Possible Primitive Earth Conditions" (PDF).  
  5. ^ Miller, Stanley L.; Harold C. Urey (1959). "Organic Compound Synthesis on the Primitive Earth".   Miller states that he made "A more complete analysis of the products" in the 1953 experiment, listing additional results.
  6. ^ A. Lazcano, J. L. Bada (2004). "The 1953 Stanley L. Miller Experiment: Fifty Years of Prebiotic Organic Chemistry". Origins of Life and Evolution of Biospheres 33 (3): 235–242.  
  7. ^ a b BBC: The Spark of Life. TV Documentary, BBC 4, 26 August 2009.
  8. ^ a b Fox, Douglas (2007-03-28). "Primordial Soup's On: Scientists Repeat Evolution's Most Famous Experiment". Scientific American. History of Science (Scientific American Inc.). Retrieved 2008-07-09. 
    Cleaves, H. J.; Chalmers, J. H.; Lazcano, A.; Miller, S. L.; Bada, J. L. (2008). "A Reassessment of Prebiotic Organic Synthesis in Neutral Planetary Atmospheres". Origins of Life and Evolution of Biospheres 38 (2): 105–115.   pdf
  9. ^ a b Bada, Jeffrey L. (2013). "New insights into prebiotic chemistry from Stanley Miller's spark discharge experiments". Chemical Society Reviews 42 (5): 2186.  
  10. ^  
  11. ^ "EXOBIOLOGY: An Interview with Stanley L. Miller". Retrieved 2009-08-20. 
  12. ^  
  13. ^ "Astrobiology Collection: Miller-Urey Apparatus". 
  14. ^ Origin of Life on Earth by Leslie E. Orgel
  15. ^ Exploring Organic Environments in the Solar System (2007)
  16. ^ Oró J, Kimball AP (August 1961). "Synthesis of purines under possible primitive earth conditions. I. Adenine from hydrogen cyanide". Archives of biochemistry and biophysics 94: 217–27.  
  17. ^ Oró J, Kamat SS (April 1961). "Amino-acid synthesis from hydrogen cyanide under possible primitive earth conditions". Nature 190 (4774): 442–3.  
  18. ^ Oró J (1967). Fox SW, ed. Origins of Prebiological Systems and of Their Molecular Matrices. New York Academic Press. p. 137. 
  19. ^ Krehl, Peter O. K. (2009). History of Shock Waves, Explosions and Impact: A Chronological and Biographical Reference.  
  20. ^ Wilde, Kenneth A.; Bruno J. Zwolinski and Ransom B. Parlin (July 1953). O Mixtures in a High-Frequency Electric Arc"2, 2"The Reaction Occurring in CO.  
  21. ^ Synthesis of organic compounds from carbon monoxide and water by UV photolysis
  22. ^ Green, Jack (2011). "Academic Aspects of Lunar Water Resources and Their Relevance to Lunar Protolife". International Journal of Molecular Sciences 12 (9): 6051–6076.  
  23. ^ "Right-handed amino acids were left behind".  
  24. ^ Kojo, Shosuke; Hiromi Uchino, Mayu Yoshimura and Kyoko Tanaka (October 2004). "Racemic D,L-asparagine causes enantiomeric excess of other coexisting racemic D,L-amino acids during recrystallization: a hypothesis accounting for the origin of L-amino acids in the biosphere". Chemical Communications (19): 2146–2147.  
  25. ^ Ruiz-Mirazo, Kepa; Briones, Carlos; de la Escosura, Andrés (2014). "Prebiotic Systems Chemistry: New Perspectives for the Origins of Life". Chemical Reviews 114 (1): 285–366.  
  26. ^ "Early Earth atmosphere favorable to life: study". University of Waterloo. Retrieved 2005-12-17. 
  27. ^ Fitzpatrick, Tony (2005). "Calculations favor reducing atmosphere for early earth – Was Miller–Urey experiment correct?". Washington University in St. Louis. Retrieved 2005-12-17. 
  28. ^ Nunn, JF (1998). "Evolution of the atmosphere". Proceedings of the Geologists' Association. Geologists' Association 109 (1): 1–13.  
  29. ^ Raulin, F; Bossard, A (1984). "Organic syntheses in gas phase and chemical evolution in planetary atmospheres.". Advances in Sspace Research 4 (12): 75–82.  
  30. ^ Raulin, François; Brassé, Coralie; Poch, Olivier; Coll, Patrice (2012). "Prebiotic-like chemistry on Titan". Chemical Society Reviews 41 (16): 5380.  
  31. ^ Thompson WR, Murray BG, Khare BN, Sagan C (December 1987). "Coloration and darkening of  
  32. ^ PIERAZZO, E.; CHYBA C.F. (2010). "Amino acid survival in large cometary impacts". Meteoritics & Planetary Science 34 (6): 909–918.  
  33. ^ Brooks D.J., Fresco J.R., Lesk A.M. & Singh M. (October 1, 2002). "Evolution of amino acid frequencies in proteins over deep time: inferred order of introduction of amino acids into the genetic code". Molecular Biology and Evolution 19 (10): 1645–55.  
  34. ^ Johnson AP, Cleaves HJ, Dworkin JP, Glavin DP, Lazcano A, Bada JL (October 2008). "The Miller volcanic spark discharge experiment". Science 322 (5900): 404.  
  35. ^ Lost' Miller–Urey Experiment Created More Of Life's Building Blocks"'". Science Daily. October 17, 2008. Retrieved 2008-10-18. 


In 2008, a group of scientists examined 11 vials left over from Miller's experiments of the early 1950s. In addition to the classic experiment, reminiscent of carbonyl sulfide there could have helped these molecules form peptides.[34][35]

[7] Professor

In recent years, studies have been made of the species, assumed to share only the last universal ancestor (LUA) of all extant species. These studies found that the products of these areas are enriched in those amino acids that are also most readily produced in the Miller–Urey experiment. This suggests that the original genetic code was based on a smaller number of amino acids – only those available in prebiotic nature – than the current one.[33]

Recent related studies

hypothesis. panspermia This has been used to infer an origin of life outside of Earth: the [32] Conditions similar to those of the Miller–Urey experiments are present in other regions of the

Extraterrestrial sources

More recent results may question these conclusions. The University of Waterloo and University of Colorado conducted simulations in 2005 that indicated that the early atmosphere of Earth could have contained up to 40 percent hydrogen—implying a much more hospitable environment for the formation of prebiotic organic molecules. The escape of hydrogen from Earth's atmosphere into space may have occurred at only one percent of the rate previously believed based on revised estimates of the upper atmosphere's temperature.[26] One of the authors, Owen Toon notes: "In this new scenario, organics can be produced efficiently in the early atmosphere, leading us back to the organic-rich soup-in-the-ocean concept... I think this study makes the experiments by Miller and others relevant again." Outgassing calculations using a chondritic model for the early earth complement the Waterloo/Colorado results in re-establishing the importance of the Miller–Urey experiment.[27]

Originally it was thought that the primitive secondary atmosphere contained mostly ammonia and methane. However, it is likely that most of the atmospheric carbon was CO2 with perhaps some CO and the nitrogen mostly N2. In practice gas mixtures containing CO, CO2, N2, etc. give much the same products as those containing CH4 and NH3 so long as there is no O2. The hydrogen atoms come mostly from water vapor. In fact, in order to generate aromatic amino acids under primitive earth conditions it is necessary to use less hydrogen-rich gaseous mixtures. Most of the natural amino acids, hydroxyacids, purines, pyrimidines, and sugars have been made in variants of the Miller experiment.[9][25]

Some evidence suggests that Earth's original atmosphere might have contained fewer of the reducing molecules than was thought at the time of the Miller–Urey experiment. There is abundant evidence of major volcanic eruptions 4 billion years ago, which would have released carbon dioxide, nitrogen, hydrogen sulfide (H2S), and sulfur dioxide (SO2) into the atmosphere.[22] Experiments using these gases in addition to the ones in the original Miller–Urey experiment have produced more diverse molecules. The experiment created a mixture that was racemic (containing both L and D enantiomers) and experiments since have shown that "in the lab the two versions are equally likely to appear";[23] however, in nature, L amino acids dominate. Later experiments have confirmed disproportionate amounts of L or D oriented enantiomers are possible.[24]

Earth's early atmosphere

More recent experiments by chemists Jeffrey Bada, one of Miller's graduate students, and Jim Cleaves at Scripps Institution of Oceanography of the University of California, San Diego (in La Jolla, CA) were similar to those performed by Miller. However, Bada noted that in current models of early Earth conditions, carbon dioxide and nitrogen (N2) create nitrites, which destroy amino acids as fast as they form. However, the early Earth may have had significant amounts of iron and carbonate minerals able to neutralize the effects of the nitrites. When Bada performed the Miller-type experiment with the addition of iron and carbonate minerals, the products were rich in amino acids. This suggests the origin of significant amounts of amino acids may have occurred on Earth even with an atmosphere containing carbon dioxide and nitrogen.[8]


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