According to the Miller-Urey experiment, the early earth atmosphere could have supported the formation of amino acids - and the experiment is hailed as being important in the 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?

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    $\begingroup$ "the experiment is hailed as being important in the explanation for the origin of life" Please consult sources that discuss this and note exactly they say, i.e. why they think this experiment is important. Any source that does not say so is of no use to you, but I am sure you will find respectable sources that provide reasons. If you still want to know the significance of the Miller-Urey experiment, update your question explaining what you do not understand. But do research and pose precise questions on a topic that can only have arguments for answers. $\endgroup$
    – David
    Mar 24, 2021 at 13:14
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    $\begingroup$ Disagree with David. This is a common question and does not need reducing. $\endgroup$
    – S Pr
    Mar 24, 2021 at 13:58

2 Answers 2


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. $\endgroup$ 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
    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. $\endgroup$ Mar 24, 2021 at 16:41

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
    Mar 24, 2021 at 16:17

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