Miller-Urey Experiment

Stanley Miller and Harold Urey in 1953 tested the Oparin-Haldane Theory and were successful in producing the organic molecules from some inorganic compounds which were thought to be present at the time of pre – biotic earth; this experiment is known as Miller-Urey experiment.

Water vapour, methane, ammonia, and molecular hydrogen were mixed with warm water, and the created atmosphere was then stimulated with electrical charges. The various elements were designed to represent, respectively, the early ocean, the early atmosphere, and heat (in the shape of lightning). One week later Miller and Urey found that simple organic molecules, including amino acids (the building blocks of proteins), had formed under the simulated conditions of early Earth.

The experiment

The apparatus included a spark chamber with two electrodes (to simulate lightning), a boiling flask (to simulate evaporation and circulation), and a condenser (to simulate raining and Haldane’s soup). A control apparatus, but without electrodes in the spark chamber, was also prepared. Miller employed a combination of methane, ammonia, hydrogen, and water. The mixture was subjected to electric discharges, which were followed by condensation and boiling. . It continued for a total of 18 days more. There were several runs of the trial. The compounds were extracted and identified using chromatography. Chromatography was used to extract and identify and analyse the compounds. Miller identified 15 amino acids (like, glycine, alanine, aspartic acid, glutamic acid), organic acids (like, lactic acid, succinic acid, propionic acid, acetic acid), a ribose sugar, and purine adenine.

The sensors are in the other flask, which has half as much water as the first. The chemical mixture received the heated water vapour after it had been introduced to it. The apparatus was surrounded by swirling gases that replicated the Earth’s atmosphere. While the water vapour symbolises water evaporating from lakes and seas, the water in the flask represents water on the earth’s surface. The electrodes were used to start the fire in order to mimic lighting and a storm using water vapour as a medium. Water collected as the vapours cooled. In a continuous loop, the condensed water goes back to the first water flask. After a week, Miller and Urey looked at the chilled water and found that 10-15% of the carbon was in the form of carbon dioxide.

Significance of Miller-Urey Experiment

1. It represents a major advance in the study of the origin of life.
2. Even though the details of the origin of life have been changed, the first stage was chemical evolution, which was proved by Miller and Urey.
3. The experiment laid a groundwork for further studies.
4. The basic result i.e. organic molecules formed from inorganic matter are still valid.
5. The electrical discharges produced during lightning in the primitive earth’s atmosphere, which contained hydrogen, ammonia, nitrogen, and water vapour, could have resulted in the formation of amino acids and other essential building blocks (Sugars, Nucleotides, and so on) of living organisms.
6. The Miller and Urey experiment provided support for Oparin and Haldane’s biochemical theory of life’s origin.
7. Miller and Urey’s experiment shows that it is possible to transition from the inorganic to the biological organic level.
8. It also demonstrates that life in the ocean began at the molecular level and progressed to the cellular level. The abiotic synthesis of organic molecules is demonstrated in this experiment.

Criticism of Miller-Urey Experiment

1. The experiment fell short of explaining how proteins were in charge of creating amino acids. 
2. Some experts disagree, claiming that the gases used by Miller and Urey are not as prevalent as the experiment indicates. They held that gases like oxygen, nitrogen, and carbon dioxide are released during volcanic explosions and make up the atmosphere. The outcomes are therefore unreliable.
3. The experiment lacked larger macromolecules like proteins and DNA that are essential for living.
4. To reduce the risk of contamination, intricate tests should be conducted in a sealed, inert, and sterilised environment. Miller, however, used a glass device to conduct his experiment. In the experimental broth, the borosilicate glass roughly disintegrated and altered the amount of amino acids produced, which is not observed when experiments are conducted in teflon equipment.
5. The main idea was that the primitive earth’s conditions were only hypothesised and might not be true.

Abiogenesis and Miller-Urey Experiment 

The Oparin-Haldane theory and the Miller-Urey experiment share many of the same foundational ideas with contemporary abiogenesis theories. The various models that have been proposed to explain the development from abiogenic molecule to living organism do, however, differ slightly, and explanations differ as to whether complex organic molecules first became self-replicating entities lacking metabolic functions or first became metabolising protocells that then developed the ability to self-replicate.

Organic molecules can form from abiogenic materials under the constraints of Earth’s prebiotic atmosphere, as demonstrated by the Miller-Urey experiment.

Conclusion

Analysis in meteorite content also revealed similar kinds of compounds indicating similar processes are occurring in space as well. The chemical evolution part of Miller-Urey conjecture was accepted.

References

1. Rogers, K. (2023, February 15). Abiogenesis. Encyclopedia Britannica. https://www.britannica.com/science/abiogenesis . Accessed on 04 March 2023.
2. Gishlick Alan. Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is wrong. National Center for Science Education. https://ncse.ngo/files/pub/creationism/icons/gishlick_icons1.pdf. Accessed on 04 March 2023.
3. Parker, E. T., Cleaves, J. H., Burton, A. S., Glavin, D. P., Dworkin, J. P., Zhou, M., Bada, J. L., & Fernández, F. M. (2014). Conducting miller-urey experiments. Journal of visualized experiments: JoVE, (83), e51039. https://doi.org/10.3791/51039 . Accessed on 04 March 2023.
4. Miller SL. Production of Some Organic Compounds under Possible Primitive Earth Conditions. J. Am. Chem. Soc. 1955;77:2351–2361.