the urey experiment

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Miller-Urey Experiment

The Miller-Urey Experiment was a landmark experiment to investigate the chemical conditions that might have led to the origin of life on Earth. The scientist Stanley Miller, under the supervision of the Nobel laureate scientist Harold Urey conducted it in 1952 at the University of Chicago. They tried to recreate the conditions that could have existed in the first billion years of the Earth’s existence (also known as the Early Earth) to check the said chemical transformations.

Miller-Urey Experiment And The Primordial Soup Theory

The experiment tested the primordial or primeval soup theory developed independently by the Soviet biologist A.I. Oparin and English scientist J.B.S. Haldane in 1924 and 1929 respectively. The theory propounds the idea that the complex chemical components of life on Earth originated from simple molecules occurring naturally in the reducing atmosphere of the Early Earth, sans oxygen. Lightning and rain energized the said atmosphere to create simple organic compounds that formed an organic “soup”. The so-called soup underwent further changes giving rise to more complex organic polymers and finally life.

The Miller-Urey Experiment In Support Of Abiogenesis

From what was explained in the previous paragraph, it can undoubtedly be considered as a classic experiment to demonstrate abiogenesis. For those who are not conversant with the term, abiogenesis is the process responsible for the development of living beings from non-living or abiotic matter. It is thought to have taken place on the Earth about 3.8 to 4 billion years ago.

Miller-Urey Experiment Apparatus and Procedure

The groundbreaking experiment used a sterile glass flask of 5 liters attached with a pair of electrodes, to hold water (H 2 O), methane (CH 4 ), ammonia (NH 3 ) and hydrogen (H 2 ), the major components of primitive Earth. This was connected to another glass flask of 500 ml capacity half filled with water. On heating it, the water vaporized to fill the larger container with water vapor. The electrodes induced continuous electrical sparks in the gas mixture to simulate lightning. When the gas was cooled, the condensed water made its way into a U-shaped trap at the base of the apparatus.

After electrical sparking had continued for a day, the solution in the trap turned pink in color. At the end of a week, the boiling flask was removed, and mercuric chloride added to prevent microbial contamination. After stopping the chemical reaction, the scientist duo examined the cooled water collected to find that 10-15% of the carbon present in the system was in the form of organic compounds. 2% of carbon went into the formation of various amino acids, including 13 of the 22 amino acids essential to make proteins in living cells, glycine being the most abundant.

Though the result was the production of only simple organic molecules and not a complete living biochemical system, still the simple prebiotic experiment could, to a considerable extent, prove the primordial soup hypothesis.

Miller-Urey Experiment Animation

Chemistry of the miller and urey experiment.

The components of the mixture can react among themselves to produce formaldehyde (CH 2 O), hydrogen cyanide (HCN) and other intermediate compounds.

CO 2 → CO + [O] (atomic oxygen)

CH 4 + 2[O] → CH 2 O + H 2 O

CO + NH 3 → HCN + H 2 O

CH 4 + NH 3 → HCN + 3H 2

The ammonia, formaldehyde and HCN so produced react by a process known as Strecker synthesis to form biomolecules including amino acids.

CH 2 O + HCN + NH 3 → NH 2 -CH 2 -CN + H 2 O

NH 2 -CH 2 -CN + 2H 2 O → NH 3 + NH 2 -CH 2 -COOH (glycine)

In addition to the above, formaldehyde and water can react by Butlerov’s reaction to produce a variety of sugars like ribose, etc.

Though later studies have indicated that the reducing atmosphere as replicated by Miller and Urey could not have prevailed on primitive Earth, still, the experiment remains to be a milestone in synthesizing the building blocks of life under abiotic conditions and not from living beings themselves.

https://www.bbc.co.uk/bitesize/guides/z2gjtv4/revision/1

https://www.juliantrubin.com/bigten/miller_urey_experiment.html

Article was last reviewed on Thursday, February 2, 2023

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One response to “Miller-Urey Experiment”

This experiment is currently seen as not sufficient to support abiogenesis. See Stephen C. Meyer, James Tour.

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Scientists recreated classic origin-of-life experiment and made a new discovery

1952 Miller-Urey experiment showed organic molecules forming from inorganic precursors.

In 1952, a University of Chicago chemist named Stanley Miller and his adviser, Harold Urey, conducted a famous experiment . Their results, published the following year, provided the first evidence that the complex organic molecules necessary for the emergence of life ( abiogenesis ) could be formed using simpler inorganic precursors, essentially founding the field of prebiotic chemistry. Now a team of Spanish and Italian scientists has recreated that seminal experiment and discovered a contributing factor that Miller and Urey missed. According to  a new paper published in the journal Scientific Reports, minerals in the borosilicate glass used to make the tubes and flasks for the experiment speed up the rate at which organic molecules form.

In 1924 and 1929, respectively, Alexander Oparin and J.B.S. Haldane had hypothesized that the conditions on our primitive Earth would have favored the kind of chemical reactions that could synthesize complex organic molecules from simple inorganic precursors—sometimes known as the " primordial soup " hypothesis. Amino acids formed first, becoming the building blocks that, when combined, made more complex polymers.

Miller set up an apparatus to test that hypothesis by simulating what scientists at the time believed Earth's original atmosphere might have been. He sealed methane, ammonia, and hydrogen inside a sterile 5-liter borosilicate glass flask, connected to a second 500-ml flask half-filled with water. Then Miller heated the water, producing vapor, which in turn passed into the larger flask filled with chemicals, creating a mini-primordial atmosphere. There were also continuous electric sparks firing between two electrodes to simulate lighting. Then the "atmosphere" was cooled down, causing the vapor to condense back into water. The water trickled down into a trap at the bottom of the apparatus.

That solution turned pink after one day and deep red after a week. At that point, Miller removed the boiling flask and added barium hydroxide and sulfuric acid to stop the reaction. After evaporating the solution to remove any impurities, Miller tested what remained via paper chromatography. All known life consists of just 20 amino acids. Miller's experiment produced five amino acids, although he was less certain about the results for two of them.

When Miller showed his results to Urey, the latter suggested a paper should be published as soon as possible. (Urey was senior but generously declined to be listed as co-author, lest this lead to Miller getting little to no credit for the work.) The paper appeared in 1953 in the journal Science. "Just turning on the spark in a basic pre-biotic experiment will yield 11 out of 20 amino acids," Miller said in a 1996 interview . The original apparatus has been on display at the Denver Museum of Nature and Science since 2013.

Miller died in 2007. Shortly before he passed, one of his students, Jeffrey Bada, now at the University of San Diego, inherited all his mentor's original equipment. This included several boxes filled with vials of dried residues from the original experiment. Those 1952 samples were re-analyzed the following year using the latest chromatography methods, revealing that the original experiment actually produced even more compounds (25) than had been reported at the time.

Miller had also performed additional experiments simulating conditions similar to those of a water-vapor-rich volcanic eruption, which involved spraying steam from a nozzle at the spark discharge. Bada and several colleagues re-analyzed the original samples from those experiments, too, and found this environment produced 22 amino acids, five amines, and several hydroxylated molecules. So the original experiments were even more successful than Miller and Urey realized.

There have been many, many more experiments on abiogenesis over the ensuing decades, but co-author Joaquin Criado-Reyes of the Universidad de Granada in Spain and his collaborators thought that one potential factor had been overlooked: the role of the borosilicate glass that comprised the flasks and tubes Miller had used. They noted that Miller's simulated atmosphere was highly alkaline, which should cause the silica to dissolve. "Therefore, it could be expected that upon contact of the alkaline water with the inner wall of the borosilicate flask, even this reinforced glass will slightly dissolve, releasing silica and traces of other metal oxides [into the vapor]," the authors wrote.

To test their hypothesis, Criado-Reyes et al . recreated three versions of the Miller-Urey experiment, mostly using the same chemicals and equipment. One version used the same borosilicate flasks Miller had used; another version used a Teflon flask; and a third version used a Teflon flask with pieces of borosilicate submerged in the water.

The results: far fewer organic compounds formed in the experiments using just the Teflon flasks. As geologist David Bressan wrote at Forbes :

Miller and Urey used equipment made from borosilicate glass as this special type of heat-resistant material is commonly used in chemical laboratories all over the world. But the new experiment shows how similar materials may have played a major role in the origin of life on Earth. More than 90 percent of Earth’s crust is made up of silicates, minerals composed predominantly of silicon-dioxide . Weathering of silicate minerals by the corrosive primordial atmosphere and water may have provided the right conditions for the assembly of the first building blocks of life on Earth.

This finding supports the authors' original hypothesis. Corrosion on the surface of the glass (due to the hot and caustic water circulating through it) plays a key role, since this releases silicon-dioxide molecules into the solution. This in turn acts as a catalyst to speed up the chemical reactions between the nitrogen, carbon, and hydrogen atoms that ultimately create organic molecules. In addition, they found that the corrosion on the glass also forms millions of tiny pits. The authors think those pits could serve as tiny reaction chambers, also speeding up the rate at which organic molecules form in the experiment.

These results are consistent with recent suggestions that it was the combination of a reduced atmosphere, electrical storms, silicate-rich rocky surfaces, and liquid water that led to the origin of life. "Miller recreated in his experiments the atmosphere and waters of the primitive Earth," the authors concluded. "The role of the rocks was hidden in the walls of the reactors."

DOI: Scientific Reports, 2021. 10.1038/s41598-021-00235-4  ( About DOIs ).

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Miller Urey Experiment

Miller and urey experiment.

Stanley L. Muller and Harold C. Urey performed an experiment to describe the origin of life on earth. They were of the idea that the early earth’s atmosphere was able to produce amino acids from inorganic matter. The two biologists made use of methane, water, hydrogen, and ammonia which they considered were found in the early earth’s atmosphere. The chemicals were sealed inside sterile glass tubes and flasks connected together in a loop and circulated inside the apparatus.

One flask is half-filled with water and the other flask contains a pair of electrodes. The water vapour was heated and the vapour released was added to the chemical mixture. The released gases circulated around the apparatus imitating the earth’s atmosphere. The water in the flask represents the water on the earth’s surface and the water vapour is just like the water evaporating from lakes, and seas. The electrodes were used to spark the fire to imitate lightning and storm through water vapour.

The vapours were cooled and the water condensed. This condensed water trickles back into the first water flask in a continuous cycle. Miller and Urey examined the cooled water after a week and observed that 10-15% of the carbon was in the form of organic compounds. 2% of carbon had formed 13 amino acids . Yet, the Miller and Urey experiments were condemned by their fellow scientists.

Also read: Origin Of Life

Criticism of the Miller Urey Experiment

The experiment failed to explain how proteins were responsible for the formation of amino acids. A few scientists have contradicted that the gases used by Miller and Urey are not as abundant as shown in the experiment. They were of the notion that the gases released by the volcanic eruptions such as oxygen, nitrogen, and carbon dioxide make up the atmosphere. Therefore, the results are not reliable.

Oparin and Haldane

In the early 20th century, Oparin and Haldane suggested that if the atmosphere of the primitive earth was reducing and if it had sufficient supply of energy such as ultraviolet radiations and lightning, organic compounds would be synthesized at a wide range.

Oparin believed that the organic compounds would have undergone a series of reactions to form complex molecules. He suggested that the molecules formed coacervates in the aqueous environment.

Haldane proposed that the atmosphere of the primordial sea was devoid of oxygen, and was a composed of ammonia, carbon dioxide, and ultraviolet light. This gave rise to a host of organic compounds. The sea contained large amounts of organic monomers and polymers, and the sea was called a ‘hot dilute soup’. He conceived that the polymers and monomers acquired lipid membranes. The molecules further developed and gave rise to the first living organism. ‘Prebiotic soup’ was the term coined by Haldane.

Also read: Evolution of Life on Earth

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Miller-Urey Revisited

Members of NAI ’s Carnegie Institution of Washington, Indiana University, and NASA Goddard Space Flight Center Teams and their colleagues have revisited the Miller-Urey experiments, and found some surprising results.

A classic experiment proving amino acids are created when inorganic molecules are exposed to electricity isn’t the whole story, it turns out. The 1953 Miller-Urey Synthesis had two sibling studies, neither of which was published. Vials containing the products from those experiments were recently recovered and reanalyzed using modern technology. The results are reported in this week’s Science .

One of the unpublished experiments by American chemist Stanley Miller (under his University of Chicago mentor, Nobelist Harold Urey) actually produced a wider variety of organic molecules than the experiment that made Miller famous. The difference between the two experiments is small — the unpublished experiment used a tapering glass “aspirator” that simply increased air flow through a hollow, air-tight glass device. Increased air flow creates a more dynamic reaction vessel, or “vapor-rich volcanic” conditions, according to the present report’s authors.

“The apparatus Stanley Miller paid the least attention to gave the most exciting results,” said Adam Johnson, lead author of the Science report. “We suspect part of the reason for this was that he did not have the analytical tools we have today, so he would have missed a lot.”

Johnson is a doctoral student in IU Bloomington’s Biochemistry Program. His advisor is biogeochemist Lisa Pratt, professor of geological sciences and the director of NASA ’s Indiana-Princeton-Tennessee Astrobiology team.

In his May 15, 1953, article in Science, “A Production of Amino Acids Under Possible Primitive Earth Conditions,” Miller identified just five amino acids: aspartic acid, glycine, alpha-amino-butyric acid, and two versions of alanine. Aspartic acid, glycine and alanine are common constituents of natural proteins. Miller relied on a blotting technique to identify the organic molecules he’d created — primitive laboratory conditions by today’s standards. In a 1955 Journal of the American Chemical Society paper, Miller identified other compounds, such as carboxylic and hydroxy acids. But he would not have been able to identify anything present at very low levels.

Johnson, Scripps Institution of Oceanography marine chemist Jeffrey Bada (the present Science paper’s principal investigator), National Autonomous University of Mexico biologist Antonio Lazcano, Carnegie Institution of Washington chemist James Cleaves, and NASA Goddard Space Flight Center astrobiologists Jason Dworkin and Daniel Glavin examined vials left over from Miller’s experiments of the early 1950s. Vials associated with the original, published experiment contained far more organic molecules than Stanley Miller realized — 14 amino acids and five amines. The 11 vials scientists recovered from the unpublished aspirator experiment, however, produced 22 amino acids and the same five amines at yields comparable to the original experiment.

“We believed there was more to be learned from Miller’s original experiment,” Bada said. “We found that in comparison to his design everyone is familiar with from textbooks, the volcanic apparatus produces a wider variety of compounds.”

Johnson added, “Many of these other amino acids have hydroxyl groups attached to them, meaning they’d be more reactive and more likely to create totally new molecules, given enough time.”

The results of the revisited experiment delight but also perplex.

What is driving the second experiment’s molecular diversity? And why didn’t Miller publish the results of the second experiment?

A possible answer to the first question may be the increased flow rate itself, Johnson explained. “Removing newly formed molecules from the spark by increasing flow rate seems crucial,” he said. “It’s possible the jet of steam pushes newly synthesized molecules out of the spark discharge before additional reactions turn them into something less interesting. Another thought is that simply having more water present in the reaction allows a wider variety of reactions to occur.”

An answer to the second question is relegated to speculation — Miller, still a hero to many scientists, succumbed to a weak heart in 2007. Johnson says he and Bada suspect Miller wasn’t impressed with the experiment two’s results, instead opting to report the results of a simpler experiment to the editors at Science.

Miller’s third, also unpublished, experiment used an apparatus that had an aspirator but used a “silent” discharge. This third device appears to have produced a lower diversity of organic molecules.

Research on early planetary geochemistry and the origins of life isn’t limited to Earth studies. As humans explore the Solar System, investigations of past or present extra-terrestrial life are inevitable. Recent speculations have centered on Mars, whose polar areas are now known to possess water ice, but other candidates include Jupiter’s moon Europa and Saturn’s moon Enceladus, both of which are covered in water ice. The NASA Astrobiology Institute, which supports these investigations, has taken a keen interest in the revisiting of the Miller-Urey Synthesis.

“This research is both a link to the experimental foundations of astrobiology as well as an exciting result leading toward greater understanding of how life might have arisen on Earth,” said Carl Pilcher, director of the NASA Astrobiology Institute, headquartered at NASA Ames Research Center in Mountain View, Calif.

Henderson Cleaves (Carnegie Institution for Science) also contributed to the report. It was funded with grants from the NASA Astrobiology Institute, the Marine Biological Laboratory in Woods Hole, Mass., and Mexico’s El Consejo Nacional de Ciencia y Tecnologia.

Scripps Institution of Oceanography is a research center of the University of California at San Diego.

The NASA Astrobiology Institute ( NAI ), founded in 1998, is a partnership among NASA , 16 U.S. teams and five international consortia. NAI ’s goal is to promote, conduct and lead interdisciplinary astrobiology research and to train a new generation of astrobiology researchers. For more information, see http://astrobiology.nasa.gov/nai.