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Life As We (Don't) Know It

The Urey Variation

Here’s a paper that probably doesn’t have much relevance out here in the real world, but illustrates some of the problems that we do face. Everyone remembers the Miller-Urey experiment, where a mixture of “primordial” gases (water, methane, ammonia, hydrogen) was subjected to repeated electric sparks and heat in a closed vessel. The idea was to see what sort of compounds might have been able to form in the early stages of Earth’s atmosphere, and it richly vindicated the ideas of J. B. S. Haldane and Alexander Oparin that complex chemicals could have been produced under such simple conditions. Famously, a variety of amino acids and other species were formed, and the number of compounds grows every time someone looks at such mixtures with more sensitive analytical techniques.

It’s quite possible (indeed, likely) that the prebiotic Earth had a different ratio of gases than the original experiment used, but followups invariably still produce amino acids and a “soup” of other compounds. The paper linked to above, from a group at Glasgow, runs a variation that Urey himself would have loved. It replaces all the starting materials with their deuterated forms.

As the chemists in the audience will appreciate, that can indeed make a difference. If the rate-limited step in a chemical process involves the breaking or formation of a bond to a hydrogen atom, that reaction will slow down if you use the heavier deuterium instead (which is the whole basis behind using deuterated drugs to slow down metabolic clearance). So what happens in this case? It turns out that you get the suite of amino acids, more or less as before, but a number of the other components of the mixture change. Dozens of compounds that are present in the “normal” runs aren’t there any more, and dozens of new ones are formed. The additive effect of tweaking those bond-breaking and bond-forming reactions sends things into completely new bins (at least 120 new species in all).

I know that the popular picture of the universe (well, one of the popular pictures) is of this vast, cold, empty, airless space, dry and deserted. And while there’s plenty of that out there, from another perspective, the universe is absolutely soaking with water and with what we think of as the molecules of life. All those old science fiction movies about desperate aliens coming to Earth to steal our water? Load of crap. There’s plenty of water out there. Saturn’s rings are made out of chunks of ice. The satellites of Jupiter have way more water than Earth ever could. Comets are snowballs, and Pluto is layered in ice. And along with that water, there’s plenty of methane, hydrogen, ammonia, nitrogen, and all the other simple gases you can name, and these mixtures have, over time, been heated, chilled, mixed, irradiated up and down the electromagnetic spectrum, exposed to all sorts of mineral surfaces, and zapped by gigantic electrical discharges. This latest work just tells us that the variety of compounds formed out there might be even greater than we thought, depending on the isotopic ratios that a given planet or system started out with.

The Miller-Urey experiment (with countless variations) has been running for billions of years, in other words, and when you see the colors of Jupiter and Saturn’s clouds (for example), you’re seeing the results. Those should remind organic chemists of the colorful stuff that sticks to the top of a chromatography column, and indeed, it’s probably pretty similar gunk. Amino acids, carbohydrates, nucleotides and other biomolecules are everywhere, from the insides of comets to interstellar clouds. So when we find our own biochemistry using these species, we should not be amazed, and when we eventually find other forms of life doing the same, that shouldn’t come as a surprise, either.

The surprise might be if we’re not deathly allergic to them – that would have made for some pretty odd Star Trek episodes, if Kirk and Spock beamed down to a new planet and immediate started sneezing their heads off and swelling up with anaphylactic shock. I guess we’ll deal with that problem when we get to it!



45 comments on “The Urey Variation”

  1. Lab Spend says:

    Also deuterium influences pH levels which could lead to a different type of soup.

  2. Wavefunction says:

    A few years ago I had written a post describing how one of the best ways to signal our presence to alien civilizations (or for them to us) might be to send out highly deuterated or tritiated molecules. The idea is that given the low abundance of these isotopes, it would be very unlikely for highly deuterated versions of organic molecules to be created naturally by chance (for instance, can we imagine finding naturally formed fully deuterated taxol in space?).

    1. Barry says:

      Because tritium’s half-life is just 12.3yrs, a signal sent by a tritiated compound would be legible to only a tiny part of our galaxy. Worse, if it were highly tritiated, the radiolytic decay would progressively turn the bulk of the material back into the sort of colored tarry mess Miller and Urey first isolated.

      1. Wavefunction says:

        C13-enriched NMR-active taxol would be another option. Highly unlikely to have formed naturally.

      2. fajensen says:

        Send it at relativistic speed, then. Close to light speed, the half-life will stretch out quite a while for the observers not riding the beam (Yes*, of course this has been tried a lot, also running molecules in accelerators to see what the properties do, so far nothing “funny”).

        *) Anyone who can put a good scar on the perfect face of Relativity will have a Nobel Price in physics lined up for them.

    2. Mark Thorson says:

      The Galactic Envionmental Protection Agency will come to arrest you for polluting space with hazardous chemicals.

    3. tlp says:

      Fully deuterated taxol? Sounds like a nice project for Baran lab!
      Sometime in a future… alien gradient student in cosmic natural product chemistry will be at the edge of frustration trying to solve the structure. The result (if successful) will likely upturn aliens’ theory of how elements are formed in the Universe.

      1. Barry says:

        It’s sufficient to make racemic Taxol to announce that this was a lab product and no mere secondary metabolite. No deuterium needed

        1. tlp says:

          Shush, don’t tell synthetic chemists!

        2. tlp says:

          Also, it won’t be exciting for race mic aliens

    4. Algirdas Vėlyvis says:

      In Greg Egan’s novel Diaspora, aliens use an “isotope beacon” – a planet with atmosphere where all common elements are substituted with their stable heavy isotopes to draw attention to the place. To a civilization that possesses telescopes with an attached spectrograph, this sort of thing is unmistakable.

  3. Druid says:

    Space is full of free electrons and ultraviolet photons, blasted out of stars. Small organic molecules in comets are treated to a lot of free radical chemistry pretty much in a form of matrix isolation (in water ice, so not inert). It may be that all the feedstock life needed was already there in the comets that brought the much-needed water to earth. 100+ organic molecules are known in space from their microwave spectra.

  4. David says:

    Truly ironic if we find a planet with breathable atmosphere, or if we terraform Mars, but still have to wear suits or breathing aparatus because most/all of us are allergic to things in the environment

    1. Pennpenn says:

      Hey, maybe by the time we’re messing around with that kind of thing we may well have developed ways to modify ourselves around the problems.

  5. Mark Thorson says:

    I wonder if adding a chunk of fluorite to the reaction vessel would result in any interesting fluorine-substituted compounds.

  6. Wile E. Coyote, Genius says:

    How would Kirk and Spock be deathly allergic to them on their first exposure? Allergic response requires prior exposure and priming of the immune system.

    1. Pennpenn says:

      So what you’re saying is Kirk and Spock would more likely be allergic to each other? (As generations of slash ficcers howl in the background)

      1. fajensen says:

        Has to be. it is well known that Captain Kirk will try to get into the pants of every alien life-form ever encountered so a very strong deterrent is needed to keep Spock “safe”.

  7. Gene says:

    “The Urey Variation” even sounds like the title of a Star Trek episode. 🙂

    1. Dr. Manhattan says:

      It’s life, Jim, but not as we know it….

  8. MoMo says:

    Its intergalactic and gaseous cloud combichem and the most advanced molecules are reading this blog.

  9. Little buddy says:

    When are we just going to start openly admitting that the PhD degree is a certificate to slave away for pfizer or other big pharma for the rest of our lives.

    1. Anon says:

      You actually think they’ll be around employing scientists for that long???

      1. Little buddy says:

        No, that’s true. But anything I can say to hasten the demise is appropriate.

  10. Little buddy says:

    For the students here, do not let your academic adviser collaborate with pharma on your phd project. It’s a complete scam. Your career will receive no benefit and your research will be slowly eroded from your control.

  11. Derek Jones says:

    The book “Life Ascending” by Nick Lane convinced me that deep ocean volcanic vents are much much better candidate for the origins of life’s basic components.

    A surprisingly detailed technical analysis of the origin of life and other major turning points of life ascending (the later chapter on consciousness is somewhat hocus pocus).

    1. Wavefunction says:

      The soup theory largely became prominent thanks to Miller and his students who also tried to suppress other plausible theories. Agree that Lane and others’ hot vents theory is more plausible, and you can find it fully fleshed out in his latest book, “The Vital Question”.

  12. Li Zhi says:

    Just watched an episode of the original Star Trek series where a charismatic hippie type took over the Enterprise and takes it to “Paradise”. A beautiful planet (iirc, no animal life??) much like mythic Paradise. The hippie cultists take a Shuttle down and one dies by biting an apple, and their (bare) feet are burned by the grass. The charismatic leader refuses to believe the planet is toxic, and he too bites the apple (dust). Anyway, the Urey et al. reactants are so dissimilar to what are now believed to be likely, I think it unfortunate that the names continue to be used as describing these ur-biochemical reactions. I’m not current with current abiogenetic models, but it seems to me that explaining how high concentrations of products persisted locally is a core (chemistry? separation science?) problem. The cascade model (materials reacting in one pool, then flowing down into another), seems interesting, but fails to explain the needed feedback. I’d guess seasonal (or other periodic) flow reversals are necessary.

    1. zero says:

      There’s a theory running around that much of this happened in ice, or at ice-water interfaces. The kinetics are much slower, so fragile molecules tend to survive longer. I suspect that seasonal melt-thaw cycles could have done something like zone refining, where molecules are concentrated according to solubility. That’s one plausible mechanism for complex organics to be concentrated.

  13. gippgig says:

    Of more relevance would be the effect of a magnetic field, and its strength, on the products.

    1. Anonymous says:

      If you are wondering about the effect of a magnetic field on enantioselectivity and the origin of chirality, look into the research fraud of: G. Zadel, C. Eisenbraun, G.-J. Wolff, E. Breitmaier, Angew. Chem. Int. Ed. Engl. 1994, 33, 454. Although it got past the referees and editors of Angew, it was quickly recognized by others that it violates physical theory and was quickly exposed when the grad student admitted to spiking his samples with chiral products.

      Don’t put your hopes in the Mother Earth’s rotation, either. Dougherty claimed to achieve “Asymmetric Synthesis in a Confined Vortex: Gravitational Fields Can Cause Asymmetric Synthesis” which also seems to violate physical theory and could not be reproduced.

      Back to Woodward 2.0, I think it was Moscovitz at Chicago who wrote extensively on some of these attempts to induce chiral selection and he was a RBW student.

      Here’s a review that also covers the concepts: “Absolute Asymmetric Synthesis under Physical Fields: Facts and Fictions”, Avalos, et al., Chem Rev, 1998, 98(7), 2391. (PAYWALL)

    2. Mike D. says:

      IMHO the biggest benefit of a magnetic field is its shielding ability against spaceborne energetic particles.

      1. fajensen says:

        And the not so energetic. Without a magnetic field, the solar wind would erode the atmosphere away and Earth would become a lot more like Mars.

  14. Anon says:

    Meh, I’d be more impressed if they did the experiment and found whole living cells created de novo.

    1. Mark Thorson says:

      Back in the 1970’s, Sidney W. Fox published some pretty interesting pictures of cell-like proteinoid microspheres created by a simulation of primordial soup washing against hot rocks. I remember one of them even had what looked like a small cell budding off a larger cell.

  15. Tom Billings says:

    Another recent and relevant experiment was using the same Miller-Urey soup, but using high velocity shock waves to provide the initiating energy for synthesis. So, where there are agglomerated masses big enough to collect an atmosphere and create lightning, you get the needed synthesis for life’s building blocks, ….and even where the same soup is brought together by bodies too small and/or too cold to hold an atmosphere, but with enough impact velocity to create shock waves, you also get the needed synthesis.

  16. James says:

    In the TIL department: The term “tholin” was coined by astronomer Carl Sagan and his colleague Bishun Khare to describe the difficult-to-characterize substances they obtained in his Miller-Urey-type experiments on the methane-containing gas mixtures such as those found in Titan’s atmosphere.

  17. Anonymous says:

    Pipeline on 21-Apr 2017 was “A Publication Dilemma” about the ethics and politics of publications. What’s the tie-in?

    There were other groups working on similar, if not identical, ideas regarding theories of the Origin of Life and the Chicagoans (Miller, Urey) were aware of it. One was the MacNevin group at Ohio State. Another was the Wilde group which submitted their paper to Science in Dec 1952. Made aware of this, Urey was able to expedite the publication of Miller’s paper which was not submitted until Feb 1953 yet it appeared two months BEFORE the Wilde paper. (Dec-July vs Feb-May)

    There were other related experiments going on around the same time, as well.

  18. gippgig says:

    As I recall, the proteinoid microsphere (microspherule?) experiment was presented in the Amateur Scientist column of Scientific American back then.

  19. Roger Moore says:

    Of course Urey would be especially chuffed about this version of the experiment, since he won his Nobel Prize for the first successful isotope enrichment of deuterium.

  20. Viroid says:

    “So when we find our own biochemistry using these species, we should not be amazed, and when we eventually find other forms of life doing the same, that shouldn’t come as a surprise, either.”
    Actually, I’d be very surprised if we found extraterrestrial life using the same biomolecules we do. Amino acids etc. might be quite common in soups of organic matter, but so are many other molecules.
    Our biochemistry might be far from the only “local minimum” in terms of biochemical robustness, if that makes sense. Furthermore, having a cell membrane made of fatty acids for example would be ill suited for living in cold places, like Titan.

  21. Little buddy says:

    PIs of the world, do you fail the robot test? That is, given the choice between a human postdoc and a robot that could do everything similarly, would you pick the robot? I did a back of the envelope calculation and 99% of PIs in America probably fail this.

    1. Jane says:

      It’s a bit off the Urey topic but I recall when I was in graduate school, the professors were all a bunch of far left pseudo-socialists. Then came talk of rights for their “employees” (post docs and graduate students) and boy did they turn far right in a hurry! How dare they tell me what I can do with my grant money etc! The hypocrisy was stunning.

  22. LR says:

    Vents, pool…

    What about this:
    DOI: 10.1038/NCHEM.2202

  23. Nile says:

    Anaphylactic shock on contact with extraterrestrial life?

    Yeah, plausible.

    I sure as hell wouldn’t try eating any: the space of all possible (or biologically-plausible) amino acids is huge, and almost anything that isn’t one of our familiar twenty is going to be toxic.

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