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Emergence of life in an inflationary universe

Tomonori Totani

2020 · Scientific Reports

Biology & medicineStatistics & probability
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From the abstract

Abstract Abiotic emergence of ordered information stored in the form of RNA is an important unresolved problem concerning the origin of life. A polymer longer than 40–100 nucleotides is necessary to expect a self-replicating activity, but the formation of such a long polymer having a correct nucleotide sequence by random reactions seems statistically unlikely. However, our universe, created by a single inflation event, likely includes more than 10 100 Sun-like stars. If life can emerge at least once in such a large volume, it is not in contradiction with our observations of life on Earth, even if the expected number of abiogenesis events is negligibly small within the observable universe that contains only 10 22 stars. Here, a quantitative relation is derived between the minimum RNA length l min required to be the first biological polymer, and the universe size necessary to expect the formation of such a long and active RNA by randomly adding monomers. It is then shown that an active RNA can indeed be produced somewhere in an inflationary universe, giving a solution to the abiotic polymerization problem. On the other hand, l min must be shorter than ~20 nucleotides for the abiogenesis probability close to unity on a terrestrial planet, but a self-replicating activity is not expected for such a short RNA. Therefore, if extraterrestrial organisms of a different origin from those on Earth are discovered in the future, it would imply an unknown mechanism at work to polymerize nucleotides much faster than random statistical processes.

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In the conversation

Original HN comments, with labels from simple text rules. A label describes the whole comment and may miss context or irony. Read the discussion to make up your own mind. About the labels

4 selected excerpts · 4 total mentions

superposeur
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The “eventually build dna base pairs” (that continue self replicating) is the uncertain and possibly ludicrously improbable step. See for instance https://www.nature.com/articles/s41598-020-58060-0 which argues for a probability per exoplanet small enough that it hasn’t happened a second time in the observable universe. On the other hand, one of the self-organizing proposals cited elsewhere in this thread may turn out to be correct and the probability may be much higher. The point is that everything hinges on the particular value of this probability and we don’t know what it is. Similar points made here: https://blogs.scientificamerican.com/cross-check/pssst-dont-...
Original comment NASA study finds life-sparking energy source and molecule at Enceladus
Calavar
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No, it's not as simple as that. The probability of self-replicating RNA arising by random assembly of bases is very low. There was a good Nature article [1] published a couple years back that digs through some of the numerical issues. (And a good, more layperson oriented summary as well [2].) The gist is that a self-replicating RNA sequence would have to be at least 40 nucleotides (and possibly even as long as 100), but the probability of randomly synthesizing a 40-nucleotide long sequence that happens to be self-replicating anywhere in the visible universe over the span of 13 billion years is effectively zero. To be fair, the probability gets closer to one if you expand…
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your view to include the entire universe and assume that it is many, many orders of magnitude larger than the visible universe. But my take away, at least, is that we are not dealing with a situation where random assembly of RNA is so likely to generate self-replicating sequences that abiogenesis was effectively an inevitability. That was the narrative I was sold in grade school and undergrad, but it appears to be wrong. There are a good number of free parameters in the journal article that I linked: The fraction of RNA sequences that are self-replicating, the fraction of planets that are habitable for life, the average decay rate of RNA on a habitable planet, etc. You take can take issue with the empirical estimates for those parameters, but that points to missing pieces in the framework: Was there a chemical process on early earth that stabilized RNA oligomers that no longer exists? Are self-replicating RNA sequences more common than we believe? If so, why haven't we encountered more of them in nature? And so on. In my opinion, these are the truly interesting questions, not whether nucleotides and amino acids can form spontaneously. [1] https://www.nature.com/articles/s41598-020-58060-0 [2] https://mathscholar.org/2020/05/the-origin-of-life-in-an-inf...
Original comment Scientists discover new “origins of life” chemical reactions
tepitoperrito
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Meta comment first: Man, I hate SEO spam and I long for more diversity in powerful search engines (one's tailored for scientific research, some tailored to religious scholarship, etc). Because searching "abiogenisis facing theoretical problems" is like 90% theological bent spam that would fail scientific rigor (I am not agnostic or atheist either). This is what I found on the first page of google that I felt like reading the abstract for if anyone's curious: https://www.nature.com/articles/s41598-020-58060-0
Original comment Diversity of extraterrestrial purine and pyrimidine in carbonaceous meteorites
superposeur
Neutral mention · rule
It is “important to remember” precisely because these days people are not remembering this and speak with a sense of inevitability about discovering life elsewhere, which sense of inevitability is totally unsupported. I may gently point out, your own post says “it is only a matter of time before science can connect the dots”, reflecting this (in my view) distorted sense. The abiogenesis research you cite is absolutely worthwhile, but it is not even clear if it is in the right direction and certainly far, far from successfully sparking the sustained chain reaction of life. To my eye, equally consistent (as some different research may suggest) is that a combinatorial needle must be threaded to the tune of p < 10^-23 per exoplanet, making it unlikely to happen again in our observable universe. Edit: to cite just the one “combinatorial abiogenesis” reference, see for instance https://www.nature.com/articles/s41598-020-58060-0
Original comment NASA study finds life-sparking energy source and molecule at Enceladus

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