According to the Miller-Urey experiment, the early earth atmosphere could have supported the formation of amino acids. This could provide an explanation for the origin of life. However, I do not understand how life could have started from amino acids (or proteins) which do not self replicate. Certain types of RNA do self-replicate, and it is plausible how life could have evolved from there.

Does it matter if amino acids came before RNA if they did? Is it correct to assume that in the RNA world, life somehow learnt how to use amino acids?


3 Answers 3


This is a common question. I think the experiment and its conclusions are often misunderstood.

Originally, the null hypothesis was that the ingredients for life could not have come about spontaneously, from inert, inorganic molecules. There was no evidence of strictly physical, non-biological processes being able to produce compounds that were necessary for the proteinaceous life as we know it. In other words, abiogenesis was therefore not supported by any line of positive evidence... until the Miller-Urey experiment. The experiment showed that the ingredients could arise through plausible, natural conditions prior to the existence of life! It bridges the gap between inert, inorganic, non-biological, and the rich soup of complex molecules that would - arguably - be necessary for anything like abiogenesis to even be a consideration based on empirical observation.

Of course the presence of amino acids is not evidence for the abiogenic origin of life. Life is not protein nor amino acid alone. But demonstrating that complex biological ingredient chemistry occurs spontaneously in large abundance - that sounds like a great take-off point for an abiogenic origin of life! That's really all the experiment achieved. In its historical context, it is a very impressive discovery, but it is certainly not a complete explanation, merely something that makes myriad biochemical explanations possible (and perhaps even plausible!). Perhaps you can now better appreciate why it excited and continues to excite biochemists working on trying to understand the chemical origins of life. The Miller-Urey experiment is foundational.

As for the transition from RNA to an RNA-protein origin of life, I quote briefly from another answer elsewhere here:

Regarding the transition from RNA-only to RNA-protein world, peptides function as cofactors for some ribozymes. Amino acids and peptides are known to have existed in the prebiotic environment and have been found in space (glycine has been found in comets, along with other 70 amino acids).

  • $\begingroup$ The actual problem with this experiment is that the environmental conditions implied in it might have never existed on Earth - at least, this is what the geologists say. $\endgroup$
    – Roger V.
    Commented Mar 24, 2021 at 14:07
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    $\begingroup$ The discussion about the historical validity of the conditions assumed in the experiment has been ongoing and rich and full of disagreement, even among experts; similar experiments have been performed with many adjustments since. It's worth taking a look into it if interested! $\endgroup$
    – S Pr
    Commented Mar 24, 2021 at 14:09
  • $\begingroup$ This is reaching back several decades, but has the Miller Urey experiment ever been replicated? I thougt not... am I mistaken? I'd love to know. $\endgroup$ Commented Mar 24, 2021 at 16:41
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    $\begingroup$ @anongoodnurse thousands of times, with thousnds of variations. Miller Urey is just the first such experiment which is why it famous. The wiki has a nice summary of follow up work en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment $\endgroup$
    – John
    Commented May 11 at 13:02
  • $\begingroup$ @John - I didn't know that! Thanks! $\endgroup$ Commented May 11 at 13:23

Answers gets more precise but conclusions are far stretched.

Going from amino acids to proteins or peptides (small proteins) is an unsolved problem. In water where they are supposed to be stored, they cannot combine. Water molecule occupies the link necessary to produce a valid amino-acid chain by which all amino-acids are linked into a protein.

Also, it is well less known that some mechanism must protect amino acids from linking by side chains, which is tough to avoid, and destroys the achievement of a correct peptide or protein. Chemists know how to do it with specialized chemicals and specialized laboratory material.

Nobody ever described a simple chemical formula to bring correctly amino acid together to form proteins, from chemical material that exists in a pre-biotic world.

Needless to say, that in the four classes of the building block of the building block of the life, amino acid, nucleotic acid, sugars, lidips, nobody knows how to pre-biotically control chemistry to assemble more complex molecules. It is almost impossible to bring a correctly linked chain of nucleotic acid in proper order (they must be obeying precise linkage (links to 3' and 5' ends). Ribose that is part of it, has still no explanation for its coming into existence in a prebiotic world.

The idea that time helps all this by failures and restart is misleading. Misaligned molecules (which is so highly inevitable) remain as they are. Source material is lost. Accumulation of chemical impurities impairs the success of having something useful. Delicate molecules like ARN have a short half-life. An extended explanation of difficulties of abiogenesis is available at https://www.youtube.com/watch?v=71dqAFUb-v0. This a seriously challenging 12 episodes series about the chemistery required for abiogenesis.

We have been raised by an education system far outdated about the difficulties of abiogenesis (that make appear it so much more possible that is was in reality). This is why no significant success were made since the 60 about this subject.

  • $\begingroup$ except self forming nucleic acid chian have been done, it is actually remarkably easy if you not keep purifiying out your samples.nature.com/articles/nature08013 and pubs.acs.org/doi/10.1021/jacs.0c12955 you may want to update your information A LOT has changed since the 60's $\endgroup$
    – John
    Commented May 11 at 12:17
  • $\begingroup$ You may want to learn prebiotic chemistry from soneone serious not a creationist shill who openly lies. youtube.com/… as an example 7 years is not a short half-life, it is more than enough time to get billions of reactions, James just lies about the relevent chemistry or worse does not understand it. $\endgroup$
    – John
    Commented May 11 at 12:55

The Miller-Urey experiment does not explain the origin of life. It just propose a plausible way to develop life from organic matter, as part of the abiogenesis model of the origin of life. A better approach to understand the theories of life origin is looking for a context.

We already know, by the cellular theory, that cell are the main component of organisms and that just cells could originate others cells. So, the research is focused on finding a way to create at least one cell. From knowed compounds, cells could be modeled as a set of autoregulated biomolecules. Just two of them are used explicitly for replication: nucleic acid and proteins. If you think about this two components, the Miller-Urey experiment just propose a way to develop simple proteins from aminoacids, and aminoacids from inorganic matter. Amazing, but not enough for explaining the complexity of actual proteins and enzymes.

But there are other theories and facts that works well with this experiment. Some non-translated olygopeptides have intracellular functions. The PAHs world theory proposes a way to develop nitrogenated bases from aromatic hydrocarbons. This bases are precursors for RNAs and DNAs. The RNAs world hypothesis establish a way to develop life from RNA and not DNA or proteins. The phospholipid bilayer have some common patterns with micelles and all this mechanisms would be part of the Last Universal Common Ancestor (LUCA). But there is no evidence of the relationships between this theories and maybe there are just too simple for explaining life.

Maybe the first cell had come from the space, where a pre-term version the krebs cycle have been demostrated to work. We could think on it as "biogenesis" until "abiogenesis" could be demonstrated.

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    $\begingroup$ "first cell from space" does not solve the problem it just side steps it, also you may be interested is some of the more recent work on RNA synthesis. pubmed.ncbi.nlm.nih.gov/33547911 $\endgroup$
    – John
    Commented Mar 24, 2021 at 16:17

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