Difference between revisions of "Miller-Urey experiment"
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===Early earth atmosphere=== | ===Early earth atmosphere=== | ||
There is significant uncertainty to what the primitive atmosphere was composed of.<ref name="Bada2013" /> The Miller-Urey experiment assumed an a primitive atmosphere was composed of ''reducing'' (oxygen poor) gases [e.g. methane (CH<sub>4</sub>), ammonia (NH<sub>3</sub>), hydrogen (H<sub>2</sub>), and water vapor (H<sub>2</sub>O)], but by the 1980s geochemists believed that early earth atmospheres probably had ''neutral'' gases like those emitted by volcanoes [e.g. water vapor (H<sub>2</sub>O), carbon dioxide (CO<sub>2</sub>), and nitrogen (N<sub>2</sub>)] and perhaps some ''reducing'' gases like carbon monoxide (CO). Since hydrogen was a light element, there probably would not have been any or perhaps very little in early earth.<ref name="wells" /><ref name="Bada2013" /> A possible source of lightning could have been "volcanic lightning", which occurs sometimes near volcanic eruption plumes, and some volcanic gases emitted have been hydrogen sulfide (H<sub>2</sub>S), ammonia (NH<sub>3</sub>), methane (CH<sub>4</sub>), and carbon dioxide (CO<sub>2</sub>).<ref name="Bada2013" /> Some scientists believe that early earth atmosphere was similar to earth today.<ref>[https://web.archive.org/web/20250902132614/https://astrobiology.nasa.gov/news/earths-early-atmosphere-an-update/ Earth's Early Atmosphere: An Update] - NASA</ref> | There is significant uncertainty to what the primitive atmosphere was composed of.<ref name="Bada2013" /> The Miller-Urey experiment assumed an a primitive atmosphere was composed of ''reducing'' (oxygen poor) gases [e.g. methane (CH<sub>4</sub>), ammonia (NH<sub>3</sub>), hydrogen (H<sub>2</sub>), and water vapor (H<sub>2</sub>O)], but by the 1980s geochemists believed that early earth atmospheres probably had ''neutral'' gases like those emitted by volcanoes [e.g. water vapor (H<sub>2</sub>O), carbon dioxide (CO<sub>2</sub>), and nitrogen (N<sub>2</sub>)] and perhaps some ''reducing'' gases like carbon monoxide (CO). Since hydrogen was a light element, there probably would not have been any or perhaps very little in early earth.<ref name="wells" /><ref name="Bada2013" /> A possible source of lightning could have been "volcanic lightning", which occurs sometimes near volcanic eruption plumes, and some volcanic gases emitted have been hydrogen sulfide (H<sub>2</sub>S), ammonia (NH<sub>3</sub>), methane (CH<sub>4</sub>), and carbon dioxide (CO<sub>2</sub>).<ref name="Bada2013" /> Some scientists believe that early earth atmosphere was similar to earth today.<ref>[https://web.archive.org/web/20250902132614/https://astrobiology.nasa.gov/news/earths-early-atmosphere-an-update/ Earth's Early Atmosphere: An Update] - NASA</ref> | ||
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| + | ====Chemical Yield==== | ||
| + | Amino acid yield in spark discharge experiments depends critically on the pH of the aqueous phase since at lower pH, amino acid production is greatly reduced and hydroxy acids in greatly increased.<ref name="Bada2013" /> Hydrothermal vents have been proposed as an alternative prebiotic chemistry source but they face severe limitations and actual synthesis have never been demonstrated using plausible geochemical conditions.<ref name="Bada2013" /> | ||
==See also== | ==See also== | ||
Revision as of 13:57, September 2, 2025
The Miller-Urey experiment was the first attempt to reverse-engineer the conditions in earth's atmosphere that produced abiogenesis – the production of life from non-life. By recent analysis, the experiment did produce quite a few amino acids, but not many of the ones used for making proteins in a cell or in any significant chemically usable quantity. Furthermore, it produced those acids in a racemic mixture (left and right handed amino acids). Life uses specific chirality (left handed amino acids only). Even secular scientists are not willing to accept this as the definitive proof of how life began.
The 1953 experiment
In the 1920s, Russian scientist A. I. Oparin and British scientist J. B. S. Haldane suggested that the Earth’s primitive atmosphere had "reducing" (oxygen poor) gases consisted mainly of methane (CH4), ammonia (NH3), hydrogen (H2), and water vapor (H2O).[1] In 1953, Stanley Miller performed an experiment with those exacts same reducing gases and reported the production of biomolecules from simple gaseous starting materials using an apparatus constructed to simulate the primordial Earth's atmosphere-ocean system. Miller used what he thought was primitive gases that would be available on a primitive earth: 200 mmHg of CH4, 100 mmHg of H2, 200 mmHg of NH3 and 200 ml of H2O into the equipment. In other words the ratio was 2:1:2:2 for CH4:H2:NH3:H2O. Then he subjected this mixture, under reflux, to an electric discharge simulating lightning for a week while the water was simultaneously heated for that time period.[2]
Results
In his original paper, Miller was able to identify some amino acids glycine, α-alanine and β-alanine while Aspartic acid and α-aminobutyric acid were less certain.[3] Miller also stated "it is estimated that the total yield of amino acids was in the milligram range" which means that very little material formed after a week of continuously running of the experiment non-stop.[3]
Re-analysis of samples and other discharge experiments
Miller had performed other experiments between 1952-1954 using two other apparatuses. A few vials of the samples he made were found in the 2000s and analyzed using modern techniques that have more sensitivity.[4][5] After modern analysis of his 1950s samples (including the 1953 experiment and volcano experiment), 31 amino acids, 6 amines, and 12 dipeptides/cyclodipeptides formed in very small amounts.[4]
| Amino Acid | Miller-Urey Experiment 1953 | Bada 2016 Re-evaluation of 1953 samples
(moles relative to glycine = 1 [where 4.8 mg was the amount of glycine synthesized]) |
|---|---|---|
| glycine | Detected | 1.0 |
| α-alanine | Detected | 0.54 |
| β-alanine | Detected | 0.24 |
| Aspartic acid | Unsure but possible | 0.006 |
| α-aminobutyric acid | Unsure but possible | 0.08 |
| a-aminoisobutyric acid | N/A | 0.002 |
| Glycolic acid | N/A | 0.89 |
| Sarcosine (N-methylglycine) | N/A | 0.08 |
| Lactic acid | N/A | 0.49 |
| N-Methylalanine | N/A | 0.02 |
| a-Hydroxybutyric acid | N/A | 0.08 |
| Succinic acid | N/A | 0.06 |
| Glutamic acid | N/A | 0.01 |
| Iminodiacetic acid | N/A | 0.09 |
| Iminoacetic-propionic acid | N/A | 0.02 |
| Formic acid | N/A | 3.70 |
| Acetic acid | N/A | 0.24 |
| Propionic acid | N/A | 0.21 |
| Urea | N/A | 0.03 |
Modern Interpretations
Early earth atmosphere
There is significant uncertainty to what the primitive atmosphere was composed of.[5] The Miller-Urey experiment assumed an a primitive atmosphere was composed of reducing (oxygen poor) gases [e.g. methane (CH4), ammonia (NH3), hydrogen (H2), and water vapor (H2O)], but by the 1980s geochemists believed that early earth atmospheres probably had neutral gases like those emitted by volcanoes [e.g. water vapor (H2O), carbon dioxide (CO2), and nitrogen (N2)] and perhaps some reducing gases like carbon monoxide (CO). Since hydrogen was a light element, there probably would not have been any or perhaps very little in early earth.[1][5] A possible source of lightning could have been "volcanic lightning", which occurs sometimes near volcanic eruption plumes, and some volcanic gases emitted have been hydrogen sulfide (H2S), ammonia (NH3), methane (CH4), and carbon dioxide (CO2).[5] Some scientists believe that early earth atmosphere was similar to earth today.[6]
Chemical Yield
Amino acid yield in spark discharge experiments depends critically on the pH of the aqueous phase since at lower pH, amino acid production is greatly reduced and hydroxy acids in greatly increased.[5] Hydrothermal vents have been proposed as an alternative prebiotic chemistry source but they face severe limitations and actual synthesis have never been demonstrated using plausible geochemical conditions.[5]
See also
References
- ↑ 1.0 1.1 Jonathan Wells. 2017. Zombie Science: More Icons of Evolution. ISBN: 978-1936599448. 3. Survival of the Fakest
- ↑ Parker, E. T., Cleaves, J. H., Burton, A. S., Glavin, D. P., Dworkin, J. P., Zhou, M., Bada, J. L., Fernández, F. M. Conducting Miller-Urey Experiments. J. Vis. Exp. (83), e51039, doi:10.3791/51039 (2014).
- ↑ 3.0 3.1 Stanley Miller. 1953. "Production of Amino Acids Under Possible Primitive Earth Conditions". Science. 117 (3046): 528–9.
- ↑ 4.0 4.1 Bada, J. L. (2016). One of the foremost experiments of the 20th century: Stanley Miller and the origin of prebiotic chemistry. Metode Science Studies Journal, (6), 183–189. https://doi.org/10.7203/metode.6.4994
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Bada JL. New insights into prebiotic chemistry from Stanley Miller's spark discharge experiments. Chem Soc Rev. 2013 Mar 7;42(5):2186-96. doi: 10.1039/c3cs35433d
- ↑ Earth's Early Atmosphere: An Update - NASA