A Fascinating Plot Twist As Researchers Recreate Classic “Primordial Soup” Experiment

Science is built on reproducibility; if someone else can replicate your results, chances are pretty good that you’re looking at the truth. And there’s no statute of limitations on reproducibility; even experiments from 70 years ago are fair game for a fresh look. A great example is this recent reboot of the 1952 Miller-Urey “primordial soup” experiment which ended up with some fascinating results.

At the heart of the Miller-Urey experiment was a classic chicken-and-the-egg paradox: complex organic molecules like amino acids and nucleic acids are the necessary building blocks of life, but how did they arise on Earth before there was life? To answer that, Stanley Miller, who in 1952 was a graduate student of Harold Urey,  devised an experiment to see if complex molecules could be formed from simpler substances under conditions assumed to have been present early in the planet’s life. Miller assembled a complicated glass apparatus, filled it with water vapor and gasses such as ammonia, hydrogen, and methane, and zapped it with an electric arc to simulate lightning. He found that a rich broth of amino acids accumulated in the reaction vessel; when analyzed, the sludge was found to contain five of the 20 amino acids.

The Miller-Urey experiment has been repeated over and over again with similar results, but a recent reboot took a different tack and looked at how the laboratory apparatus itself may have influenced the results. Joaquin Criado-Reyes and colleagues found that when run in a Teflon flask, the experiment produced far fewer organic compounds. Interestingly, adding chips of borosilicate glass to the Teflon reaction chamber restored the richness of the resulting broth, suggesting that the silicates in the glassware may have played a catalytic role in creating the organic soup. They also hypothesize that the highly alkaline reaction conditions could create microscopic pits in the walls of the glassware, which would serve as reaction centers to speed up the formation of organics.

This is a great example of a finding that seems to knock a hole in a theory but actually ends up supporting it. On the face of it, one could argue that Miller and Urey were wrong since they only produced organics thanks to contamination from their glassware. And it appears to be true that silicates are necessary for the abiotic generation of organic molecules. But if there was one thing that the early Earth was rich in, it was silicates, in the form of clay, silt, sand, rocks, and dust. So this experiment lends support to the abiotic origin of organic molecules on Earth, and perhaps on other rocky worlds as well.

[Featured image credit: Roger Ressmeyer/CORBIS, via Science History Institute]

44 thoughts on “A Fascinating Plot Twist As Researchers Recreate Classic “Primordial Soup” Experiment

  1. Add in about a billion years for some form of replicating amino acid replicating itself to take off in the soup, life has begun. When it randomly starts to change (mutations) to generate the ability to get energy from surrounding proteins to replicate itself much more quickly, life is on its way. Encapsulating itself in a selfish membrane to protect its own valuable enzymes, our fate is sealed.

    1. Armies of scientists have tried this experiments for dozens of years, and at best, managed to create 13 amino-acids used in a cell, under heavily direct circumstance. The experiment explained in this article only proves that using one material instead of others, you’d obtain LESS amino-acids.

      Where are the other amino-acids? One missing element, and life cannot appear.

      Also, AFAIK, “self replicating” amino-acids do not exist, you need to repeat the same formulas over and over to keep creating them and have to tiniest chance to start creating proteins. The chances that proteins appears, these intricate molecules, with very specific 3D shapes, is far smaller that the chance of amino-acids appearing out of a soup.

      So as you can see, “add a billion years” is at least a very simplistic way of hoping even the most simple form a life could appear. As Hubert Yockey declared, it takes a lot of faith to believe in that.

  2. I really love it when these old accepted experiments are given a new twist like this, so often the results are surprisingly interesting, and really brings home how little we really understand about the why/how/what at times.

  3. I would very much like to see this experiment repeated several times in the teflon reaction vessel – with added chips of basalt, rhyolite and various early sediment types.

    I wouldn’t mind betting that the result is more than 5 amino acids.

    I might add that the early atmosphere was probably fairly rich in sulphur dioxide, too!

    1. It’s all waffle though because in no case has anyone given the experiment anything close to a sufficient amount of time. Even a multigenerational version would be a drop in the bucket.

      1. Not necessarily. In nature, lightning strikes are more rare and happen over huge areas. By restricting the area to a flask and increasing the frequency of the lightning, you’re essentially compressing time to demonstrate what COULD happen under natural conditions given the huge amount of time you suggest.

    2. Yes, in 1970 part of my graduate work at MIT centered on the chemical analysis of the later Urey-Miller experiments with sulfur dioxide and other gases in the reaction chamber. After several days of electrical discharge there were even more compounds generated that included the insertion of sulfur into different biochemicals! These experiments centered on pseudo-Jupiter atmospheres that are assumed to be high in sulfur compounds. After a few days of electrical discharge in the reactor cells there was a dark brown tar-like residue of organic compounds. All tests were analyzed with a gas chromatography-magnetic-sector-mass spectrometry instrument in 1970-1971. The MIT results lead to a publication acknowledgement from Dr. Urey as part of my Ph.D. requirements. We used an IBM 1800 with magnetic core memory, card reader for software programming, and large tape drives to store data and programs. We have come a long way since then!

    1. PTFE was discovered by accident in 1938 by Dr. Roy Plunkett. It was first marketed by DuPont in 1945, so technically yes. But I’ll bet it was still hideously expensive in 1952 — although Tefal pans were first sold in France in 1954, so it must not have been too expensive.

    2. You’re suggesting Teflon wasn’t around during the evolution of amino acids into cellular life, right? That doesn’t matter. The teflon is supposed to be inert so that a key variable can be observed alone. Experiments don’t have to be done with the target environment when you’re trying to figure out what was the key part of that environment. Rocks, as you suggest, are often full of silicon, so that’s not a very useful experiment.

  4. I’d love to know what’s going on in that flask in the picture, electrically. The only way I can figure to get two straight line discharges toward the center like that is maybe to ground the center and apply pulsed DC to the top two electrodes alternating quickly enough for persistence of vision to make them look simultaneous.

    1. The article take from shows a rough schematic and states “continuous electric sparks firing between two electrodes to simulate lighting” with + and – to the electrodes so implying HV DC.
      Agree with Alysson Rowan that ” the early atmosphere was probably fairly rich in sulphur dioxide”,
      I would like to see this re-done in various containers with various clays and minerals available in a non-oxygenated atmosphere (don’t think this rules out limited oxides necessarily….room for argument there), without the materials used to “stop the reaction”, and a whole series of modern tools used to examine the results AFM, electron microscope, spectrometry etc.) Just for curiosity’s sake

      1. In the mid 1970s my graduate work involved analyzing meteorites, moon rock and performing the Miller-Urea experiment with variations including using D2O (deuterated water) and C13 to investigate the role of hydrogen cyanide and HCN polymers. I used a neon light transformer with the output run through a bank of resistors in series. It gave a continuous spark between two tungsten electrodes. Gas chromatography with quadrapole mass spectrometry (fairly new at the time) to analyze the results. For the electronic buffs a PDP-8 system controlled the mass spec, 9 inch disks, teletype I/O, HP plotter, paper tape cold boot. Ah, the old days – what a PITA. Had to work for days to get everything tuned and then it was don’t touch a thing, work all night when the system was running perfectly.

    1. If undersea volcanic vents were those primordial conditions, or if tidal pools were, or whatever; waves, convection, wind, all sorts of things can all push those amino acids out of those conditions rather quickly. I don’t think it was so lucky. The earth is essentially a giant bioreactor. I’d argue that most planets with liquid water are. I bet this process is extremely common in the universe. It’s just that there’s a lot of lifeless matter in between making it hard to find.

  5. There use to be a great display about the primordial soup in the Chicago Museum of Science and Industry. In a video they had Julia Childs explaining and putting together the soup as if she was following a recipe. They have some good stuff there.

  6. Ahh… curious to see how the lungs, heart, blood vessels, brain and complex neurological connections and nerves were formed over billions of years as life forms became increasingly more complex in a completely random and unintelligent sequence of events. Heck, the DNA sprung out of the primordial soup, randomly formulating male and female organisms that knew what to do to recreate their kind, nurse them, feed them, support them yet somehow didn’t go extinct in the harsh, brutal, early earth atmospheric conditions, that even wiped out dinosaurs eventually. These same living organisms evolved over billions of years until they became powerful enough to take out the entire planet with war and pollution while creating intelligent systems that required their minds even though they themselves were formed from a completely mindless process. The whole thing sounds like a fascinating bed time story, but I am confident we will find the answers in the perfectly designed and fine tuned conditions of a test tube in a lab. Science has never failed us.

    1. I recommend Cosmos by Carl Sagan. He covers all that. It’s not really a mystery or hard to understand. It’s a long slow process of tiny steps and natural selection of mutations in DNA via environmental conditions. Whether you’re humble enough to admit you’re not a god baby or not is a different story.

  7. This is cool but my worry is that everyone gets so fixated on DNA and RNA that that might be all anyone looks for in the resultant soup. I get it, people like nucleic acids because they look like *code* and we’ve all been rather bedazzled by *code* these last few decades.

    But I’d almost wager that metabolism came first. A system of self sustaining enzymes able to create more of themselves would undergo Darwinian evolution as surely as any string of nucleic acids. It seems doubtful that a single enzyme could do exploit an environmental energy gradient to replicate itself, but otoh a couple dozen cooperating molecular species might be capable of doing so. Heck, this hypothetical collection might even be made of RNA, but the distinction is between acting as specific enzymes vs being arbitrary strings of abstraction equivalent to genes. It’s easy to imagine that if the first such self propagating network were *not* RNA, that RNA could hijack it. This seems much more probable to me than does RNA somehow magically propagating itself out of free environmental nucleic acids and then somehow inventing metabolism later.

    Point being, after you run one of these for a while, do you just run a PCR and try to find DNA/RNA sequences? Or do you look for signs that the mix can assimilate further material? What if you found that you could shut the electricity off, and then add some more H2S (or whatever) and it *ate* that? Let’s not just try to prove that we can get DNA, let’s zap some primordial soup and see what we actually get, if we can get it to *do* something

    1. You’ve created a false premise here. They’re not looking for DNA at this point. It’s clear that DNA did not come first. They’re looking for the things that can fall together and create the tiny precursors to life and DNA: amino acids.

      1. I thought the creation of amino acids was not in doubt. And my point is only “let’s see what happens, and not just try to prove theories. I know, the way science gets funded, it helps to have a theory to prove or disprove. But along the way we should keep our eyes open, that’s all.

        1. The creation of amino acids wasn’t in doubt. Details about what *caused* them to form apparently had not been considered, hence these new experiments.

          Theories (hypotheses) can never be proved, they can be either supported by evidence, or disproved.

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