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Prebiotic Chemistry: Miller & Urey Experiment

Updated on March 14, 2013

“But if (and Oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc., present, that a protein compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.”

-Charles Darwin 1871


The Primordial Soup

A primordial soup sounds like some absurd dish served at an upscale New York restaurant. One that is filled with who knows what, and will end up costing a leg to acquire. While this may be an endeavor a few may wish to act upon; most will forgo it. For primordial soup is not just any old soup, it is the first soup from which life is theorized to have arisen.

Think oceans, amino acids, and the early atmosphere rather than noodles, chicken, and carrots. The concept of a primordial soup is so much more fascinating than any edible soup will ever be. In fact, it is such a fascinating idea that two scientists, and later on others, strived to recreate this soup under an environment much like that seen on the early Earth. The interesting thing is; they succeeded. These scientists were able to recreate an environment that allowed for the formation of amino acids and other organic compounds essential for life.

This “Miller -Urey Experiment,” thus called in honor of the first ever conduction carried out by our two scientists Stanley L. Miller and his graduate adviser Harold C. Urey, was mind blowing to say the least . Here we have two scientists who were able to create an environment where amino acids, the building blocks of life as we know it, prospered with nothing more than some gases, an electric current, and some heat. Well, it is a little more complex than that, but we shall explore that later.

So, what does this mean? What can this experiment possible uncover about the mysteries swirling around the early Earth and the creation of life? The Miller-Urey Experiment opened many new doors for such inquires, as well as criticism, but really, what scientific discovery does not? Amino acids, gases, heat, and a spark; interesting concept, but what does it mean?

Animated Miller-Urey Experiment

Miller & Urey's Experiment

Stanley Miller and Harold Urey, working at the University of Chicago, stumbled on a concept in 1953 that would change the approach of scientific investigation into the origins of life on early Earth. They were both intrigued about the type of environment that would be needed in order for life to begin. So, like any good scientist with the scent of discovery in the air, they formed a hypothesis and tested it.

Miller and Urey placed the gases; methane (CH4), ammonia (NH3), water (H20), and hydrogen (H2) into a closed system and manipulated them in order to see if these gases could form amino acids. In their experiment, they placed water and their gases into their closed system apparatus. The water was boiled till it vaporized. This water vapor then would then move into another flask filled with the ammonia, methane, and hydrogen where a continuous electric current ran through the system. Once thoroughly electrocuted, the gases were condensed and moved through a collecting trap. The water would then move back into the boiling flack to start the process all over again.

See, the purpose of this experiment was to recreate condition of primordial Earth. An atmosphere that Miller and Urey believed to be deprived of oxygen, swarmed with lightning storms, and constantly fluctuating in temperature. They ran this system continuously for a week before analysis. When they observed the inside of their apparatus, they saw, what essentially amounts to, a whole lot of black goo. Through the use of chromatography, Miller “observed that as much as 10-15% of the carbon was now in the form of organic compounds,”a.k.a black goo.

That’s right; Miller and Urey successfully produced amino acids and organic material; the necessary components essential for cellular life. This, as you can come to imagine, caused quiet the commotion.


Black Goo Composition

But, what was this black goo? How did Miller know to use the gases that he did under such conditions? And where did this idea come from?

Well, for nearly a century, evolutionists have been claiming, with much conviction, that life started on Earth in a "primordial soup" consisting of water chuck full of chemicals necessary for the start of life. This warm little pond was believed to have been struck by an electrical discharge, probably from a lightning bolt, which caused the chemicals to make amino acids, and eventually brought forth life on our little blue planet. From this first soup, they argued, all other life evolved.

So Miller got to work on recreating said pond. Miller knew that the outer planets were very high in hydrogen content, along with water, methane, and ammonia. So, he figured that the Earth would have a similar composition after its planetary formation. The only thing that he really needed now was an energy source to drive the reactions. Miller chose to use “an electric spark to simulate the lightning strikes” that were known to bombard early Earth, and the results were extraordinary. The thing was, Miller expected to get a tarry mass composed of thousands of compounds, but got a surprise when he conducted his chromatography analysis. Several of the compounds present in Miller’s tare “appeared as distinct spots when separated on paper by chromatography. These spot appeared purple and blue when they were sprayed with ninhydrin dye and heated, and as one might conclude, these spots turned out to be the fundamental monomers of proteins; amino acids.

So Miller proved that amino acids could be synthesized by conditions present in prebiotic Earth, but the real test would come when the scientific community took a closer look at his methods.


The Critics of this Experiment

Scientists had a big problem when it comes to investigating the origins of life on the primordial Earth. And they are not as accepting of Miller’s experiment do to many problems associated with the atmosphere of Earth. The problem is our life supporting oxygen. See, an atmosphere with oxygen equaled no amino acids and thus so critters. This is because amino acids and sugars will react with oxygen to form good old carbon dioxide (CO2). But, on the other hand, an atmosphere without oxygen equaled no ozone, and yet again, no life, since without an ozone layer (O3), ultraviolet rays would soon break down organic life .

So scientists have to come up with a way to allow for the formation of amino acids in an environment that will all for its formation and protect it from radiation. Some scientists are skeptics of it because they do not believe that many of the condition were accurate with that of early Earth. For one, while it is believed that lightning storms were very common, they did not occur in a continuous supply of energy that Miller used in his experiment to form amino acids and other organic compounds. It is now believed that the early earth's atmosphere did not contain predominantly redundant molecules either.

In the 1980’s, scientists agreed that nitrogen and carbon dioxide would have been present in high qualities because Earth was very hot at those times and composed of nickel and iron. One of the most criticized aspects of the Miller- Urey experiment was the fact that is was conducted in a closed system not exposed to the primordial atmosphere which would most likely have destroyed that which was vital for life. Another argument was the fact that the amino acids that were found on Earth could also be found in outer space.

In 1969, a meteorite recovered in Australia, was shown to be rich in amino acids. About 90 different amino acids were identified and nineteen of the amino acids could also be found on the Earth . So in theory, our amino acids could have stolen a ride to Earth via a meteorite. Or, since amino acids were proven to survive in the unfriendly depths of space, it also raised the question; could the amino acids have formed and survived while the Earth was undergoing its planet developing stage?


What's up with these Amino Acids?

Let us also look at these amino acids that Miller discovered. The thing, is that in nature, we only utilize left amino acids. Amino acids, like most every chemical, are three-dimensional structures. These little monomers are tetrahedral, so one would think that we could, in a sense, rotate a right amino acid into a left simple by giving it a twist, but that is not the case.

Think of them like gloves: a left-handed glove will not fit a right-hand . And, yes, this matters greatly. Miller’s experiment gave us both, in equal amounts, of right and left amino acids. When levo amino acids are really only needed. Our problem comes when we look at functional proteins since they cannot contain more than traces of right handed amino acids, since their forms can have very different, even fatal, effects in some circumstances.

So, over all, while Mill did succeed in presenting the science community with a new way of viewing primordial Earth, he made a few, and had a few, implausible conclusions. We have irrelevant conditions, an atmosphere that does not prove true, small yields of chemicals in wrong proportions, and a serious structural problem.


Ribonucleic acid (RNA) has the bases adenine (A), cytosine (C), guanine (G), and uracil (U). Image Credit: National Institute of General Medical Sciences
Ribonucleic acid (RNA) has the bases adenine (A), cytosine (C), guanine (G), and uracil (U). Image Credit: National Institute of General Medical Sciences | Source

Was RNA the First Fundamental Molecule for Life?

Thus we go on to what may well be the biggest problem, the pessimists of amino acids. See, proteins cannot make DNA, but can catalyze for chemical reactions that take place. But RNA, sweet old RNA, can both replicate itself and, at times, act as a catalyst.

So a group of scientists have decided to go along and say; what about RNA as being the fundamental first molecule that allowed for the development of life on Earth? They argue that RNA could initiate some of the essential functions required in the cell until modern structures could evolve.A leading scientist in this field of research, Professor Orgel calls it “the prebiotic chemist’s nightmare,” and that it is. RNA may be simpler than DNA, but it is still complex and involves a chemical structure that does not form spontaneously. As Dr. Cairns-Smith puts it, “it [would] require 14 major hurdles with 10 steps in each, giving a probability of 1 in 10109 for their successful formation. The first ribo-organism would need all the cell’s metabolic functions in order to survive and it is not evidence that such a range of functions is possible for RNA.”

So, in the sense of amino acids being our first molecules of life, we should go ahead and give Miller and Urey a high-five. This is not saying that RNA is not a possibility, just that it is not a probability.


There is Still Hope for this

And thus we have covered many of the problems that Miller is facing with his experiment. So he made a few mishaps in judgment. And possibly proposed a few conclusions that will not hold to modern research, but his research has led to so many interesting possibilities. And, hey, who knows, maybe another scientist will come around an conclude that some catastrophic event took place that allowed only levo amino acids to survive and allowed for an environment that they could flourish in.

But, rather than concentrate on what is wrong with his research, let us look at what is right. Miller devised a new way to look at early life. Amino acids are the building blocks of life, and Miller wanted to see if such things could come about with simply using a bit of what was available at the time. While not all of the gases he used were thought to have been on early Earth at the time that amino acids were forming, they did exist in space. And further testing of known compounds on Earth has shown that, when manipulated similarly to what Miller carried out, they too can form amino acids.

And, recently, Dr. Jeffrey L. Bada, ‘from the Scripps Institution of Oceanography in San Diego, who had been one of Dr. Miller’s graduate students, discovered cardboard boxes containing hundreds of vials of dried residues collected from the experiments conducted in 1953 and 1954” (Chang). These vials have to potential to shed new light on Miller’s experiments. Miller conducted more than one experiment to form amino acid, but he really only ever paid attention to the first that he became known for.

These vials have been sitting for over 50 years, and the amino acids and compounds inside may have been doing, well anything really. So, as new information on these findings becomes available, we may find the Miller was more right then believed .

The Miller-Urey Experiment

In the End

Scientists are like politicians at times. When one expresses a new idea, there are a whole heard who try to disprove it, some because they actually believe that what the founding researcher idea is incorrect, and others simply because they wish to make a name for themselves in doing so. But let us explore the question proposed here, how did life begin?

This is hardly an easy question to rectify with a few experiments and squabbling scientists. The whole process will involve a tremendous amount of work and collaboration. And even if we do ever find an answer for this, it will still be question that will plague use for quite a while. Finding that which began life, and caused all that we now know, will really just be the tip of the iceberg, per se, in the humongous world of evolution and formation. The question of life is just one of those things that humans never really want to agree on. It is almost like asking use to view the sky and, with utmost certainty, name the number of stars in the sky, but we are not at that stage yet.

While Miller’s experiment does not hold up to what current scientists believe was the true nature of the early Earth, it did plant the seed for a new way to look at how life formed. Millers experiment shows that organic compounds and amino acids have the potential to be made out of material that was present on prebiotic Earth and in outer space. And other scientist have been able to prove that amino acids could be made out of the CO, CO2, and N2 that is now believed to be the major composition of early Earth as long as no oxygen is present . Miller led to the understanding that producing amino acids is much easier than first thought.

While his methods may have not been utilized the right gases and such, without him, scientists may still not be exploring this avenue of thought. The origin of life is baffling, and its discovery shall indeed take a lot of work.


Chang, Kenneth. “From Old Vials, New Hints on Origin of Life.” NewYorkTimes. Science. 2012 Web. 23 April 2012.

Deamer, David. First Life: Dicovering the Connections between Stars, Cells, and How Life Began. London:University of California Press, 2011. Print

“Four Facts That Invalidate Miller's Experiment.” Darwinism Refuted. Molecular Biology and The Originof Life. 2005. Web. 2 May 2012.

“Miller/Urey Experiment.” Cruising Chemistry. Duke University. 2012. Web.26 April 2012.

“Origin of Life: the Early Atmosphere.” BestBibleScience. Bible Science. 2012. Web. 26 April 2012.

Peet, John Ph.D. “The Miller-Urey experiment.” Truthinscience. Truth in Science Inc. 2005-2011. Web. 24 April 2012.


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    • nicomp profile image

      nicomp really 4 years ago from Ohio, USA

      I love Wikipedia's article on the Miller–Urey experiment:

      '...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.'

      "well over 20"?

      Who wrote that, an advertising executive?

    • annajazz profile image

      Anna Marie 4 years ago from Connecticut

      Hiya nicomp,

      My thoughts exactly. Wikipedia is basically a joke when it comes to science related content. Especially considering that there are only 22 amino acids that are essential for life, so I would love to know what they mean by "well over 20" amino acids.

      Thankz for sharing.


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