Scientists suspect that the complex life that slithers and crawls through every nook and cranny on Earth emerged from a random shuffling of non-living matter that ultimately spit out the building blocks of life.
Even so, the details to support the idea are lacking.
But researchers recently got creative in figuring out the probability of life actually emerging spontaneously from such inorganic matter — a process called abiogenesis.
In the study, Tomonori Totani, a professor of astrophysics at the University of Tokyo, modeled the microscopic world of molecules across the epic scale of the entire universe to see if abiogenesis is a likely candidate for the origin of life. He was essentially looking at whether there were enough stars with habitable planets in the universe at the time to allow complexity to arise. His results, published Feb. 3 in the journal Nature (opens in new tab), show the betting odds for life emerging are not good, at least for the observable universe.
Related: 7 wild theories on the origin of life
"I hoped to find at least one realistic path of abiogenesis, to explain abiogenesis by words of science," Totani told Live Science. "Sometimes people claim that abiogenesis probability is incredibly low and that the origin of life cannot be understood by science. I, as a scientist, dreamed to find a scientific explanation of why we are here."
Totani's study looks at a leading hypothesis for abiogenesis, that life as we know it began in what researchers call an RNA world. This hypothesis suggests that before the evolution of proteins and the double-stranded genetic molecule called DNA, or deoxyribonucleic acid — which today provides the instructions for life on Earth — the world was dominated by similar but less efficient molecules called RNA, or ribonucleic acid.
In an RNA world, RNA was the first molecule capable of copying and storing information, and of starting and accelerating chemical reactions — two essential characteristics of life on Earth. This world would be a more primitive molecular world to the DNA-protein based chemistry that defines life today.
Although primitive, RNA is made up of many chemicals called monomers that link together to form a polymer. Particularly, RNA is made up of a chain of nitrogen-based molecules called nucleotides. Researchers think that in order for RNA to perform its essential function of copying itself, it needs to be composed of a chain of nucleotides longer than 40 to 60 nucleotides.
So, how would these RNA molecules made up of at least 40 to 60 nucleotides have popped up on their own? Nucleotides have been shown experimentally to randomly organize into RNA given enough time and under the right conditions. But these experiments show that the abundance of RNA rapidly decreases with the length of their chains and none of the experiments could consistently produce strands longer than 10 monomers.
"It has been experimentally confirmed that RNA polymerization can occur by a basic random process," Totani said. "Some experiments claimed that more than 50 (monomer long) RNA were produced, but these are not reproducible. One problem is that aggregates are easily mistaken for a long RNA polymer."
Totani's model uses the most conservative method of RNA polymerization, where each monomer is attached randomly one-by-one until a chain of monomers is formed. Scientists have suggested that polymers (each made up of multiple monomers) could attach to each other to speed up the process, but Totani said such a process is "highly speculative and hypothetical."
Life as we know it
Scientists think life emerged on Earth around 500 million years after the planet formed. Given that there are an estimated 10 sextillion (10^22) stars in the observable universe, it may seem that the odds of life popping up in the universe should be good. But researchers have found that the random formation of RNA with a length greater than 40 is incredibly unlikely given the number of stars — with habitable planets — in our cosmic neighborhood. There are too few stars with habitable planets in the observable universe for abiogenesis to occur within the timeframe of life emerging on Earth.
"However, there is more to the universe than the observable," Totani said in a statement. "In contemporary cosmology, it is agreed the universe underwent a period of rapid inflation, producing a vast region of expansion beyond the horizon of what we can directly observe. Factoring this greater volume [of stars with habitable planets] into models of abiogenesis hugely increases the chances of life occurring."
After our universe flashed into existence some 13.8 billion years ago during the Big Bang, it underwent a period of rapid expansion that continues today. If we think of the universe as a loaf of bread baking in the oven, our observable universe is like a bubble of air trapped in the dough, where the walls of the bubble are the farthest distance light can travel since the Big Bang. As the loaf rises (inflation), our bubble grows while other pockets of air within the bread get farther away. Our observable bubble of air is all that we can see, even though the rest of the loaf is out there.
Related: From Big Bang to Present: Snapshots of Our Universe Through Time
It is estimated that the whole universe could contain more than 1 googol (10^100) stars. When Totani factored in this new abundance of stars, he found that the emergence of life was no longer improbable, but very likely.
This may be good news for the RNA world hypothesis, though it could also mean that the search for life in the universe is a hopeless pursuit.
If life first got its start in RNA, "life on Earth was created by a very rare chance of producing a long RNA polymer," said Totani. "Most likely, Earth is the only planet harboring life in the observable universe. I predict that future observations or explorations of extraterrestrial life will yield no positive results.
If by chance, life is discovered elsewhere in our cosmic neighborhood, Totani believes it would likely be of the same origin as life on Earth. Life may have hitched a ride from comets and asteroids across interplanetary or interstellar space, seeding the local universe with life from a single origin event.
Totani's work is far from an answer to one of science's most existential questions but it may guide further research on the origins of life. Whether we are alone in the universe still remains unanswered, but if Totani's numbers tell us anything, you shouldn't bet on it.
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Originally published on Live Science.
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It appears in science, that Earth having life as unique in the universe, could be a philosophical struggle for some.
Probability models on such issues are highly debatable. I am surprised that Nature would even touch such a paper. The conclusion of the model "show the betting odds for life emerging are not good, at least for the observable universe."
That we are here offers empirical evidence which suggests the odds are highly probable. (How many 100s of billions of galaxies are there in the observable universe?!) Last time I checked, there is no need for a model for life arising on earth. There is a need to address the chemistry leading to abiogenesis on earth, and therein lies the biggest challenge. Oceanic thermal vents likely played a critical role.
Determining the mechanism of abiogenesis has the long odds, not that it actually happens. One must wonder what the good professor who wrote up this article thinks about deities, and alternative facts. A very valid question considering his odds as "not good" - which clearly indicates that we should not be here!
To pile on just a tad, the impression I get from reading this is that Professor Totani makes only a minor and trivial case for the origin of life's chemistry. In reality, it is vastly more complex then he is suggesting - indeed, almost infinitely so.
Beyond that, there is nothing he notes to even remotely model probability. much less relating it to having long odds (various comments suggest a rather bio-naive Astrophysicist). He stated "I hoped to find at least one realistic path of abiogenesis, to explain abiogenesis by words of science..." . That is a remarkable statement since even the greatest minds in biochemistry are struggling with just one or two elements that may play into it all. And he hopes to find one presumably complete path? That is certainly the definition of naive, and rather comical to be sure.
Probably the most outlandish aspect is when he (an Astrophysicist mind you) asks:
"So, how would these RNA molecules made up of at least 40 to 60 nucleotides have popped up on their own? "
This question has no validity whatsoever regarding modeling abiogensis considering it is a tiny fraction of all the chemistry involved. It is equivalent to asking:
"So, how could all the components of the universe have popped up on their own? "
Both are reasonable questions, but neither provides any consideration whatever of probability. Neither does his extended treatment of "RNA everything", never dealing with the myriad other components that are surely involved, to say nothing of the vast amount of time abiogensis would require. If he had done so, based on the "logic" used in the entirety of the article, he would certainly have proclaimed beyond any doubt whatsoever that "Abiogensis is simply not possible." That would certainly send "I think therefore I am" right out the window!
The good professor knows not of what he speaks. Probably should stick to Astrophysics and model things for which there are no direct proofs. He could always go back to school and get a Ph.D. in a life science, giving him a better understanding of the topic at hand, something he is clearly lacking in the extreme. No doubt there are a lot of Astrobiologists who would take up this bio-blasphemy and run with it.....
"It appears in science, that Earth having life as unique in the universe, could be a philosophical struggle for some."
But rod, you should know better than to keep using your joke about abiogensis and spontaneous combustion! You know perfectly well that they are not even close, and could be misleading people based on all the things you know and do not joke about.
From the accurate-but-hated Wiki :
"Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high temperatures) and finally, autoignition."
Just to set the record straight, rod does not joke around with most stuff. And he probably knows more than he should. Most are left eating his dust! :)
Biologists in general think life is common since it evolved so early here on Earth, but that language capable human analogs are rare like the elephant trunk – each trait evolved just once in 4 billion years. The consensus theory, based on biology and geology, is that life evolved in alkaline hydrothermal vents. Genome trees https://www.sciencemag.org/news/2016/07/our-last-common-ancestor-inhaled-hydrogen-underwater-volcanoes ], heat shock protein ancestor temperature ranges and cell metal content agree on that.
Recent evidence implies that evolution was not a fluke. Their mineral assemblies can produce simple hydrocarbon starter materials that can build cells out of CO2 and H2, and that was also adopted as the universal common ancestor metabolism. https://www.sciencemag.org/news/2020/03/was-life-s-first-meal?utm_campaign=news_daily_2020-03-02&et_rid=388985880&et_cid=3228349 ].
These early vents could replicate 100s of bases long RNA strands by abiotic thermocycling PCR as demonstrated in experiments. They also concentrate biomolecules many order of magnitudes over in their pores. Another recent result is that the environment maximizes membrane vesicle production out of heterogeneous lipid mixes.
Moreover, in the early ocean the simple hydrocarbons would meet reduced, dissolved catalytic iron at the ocean interface, and together with other mechanisms the vents could produce lipids, sugars, and nucleobases in its various parts. The gluconeogenesis/glycolysis could happen at the vent/ocean interface, nucleobases could be produced in the core, and lipid production could happen at the vent/crust interface from further synthesis of the simple lipids. The Fe rich ocean would sequester phosphate but the mineral filtered and pH buffered vents would likely not. Such vents could also produce the ammonia that went into nucleobases before enzyme evolution, so that nitrogen instead was pulled from the atmosphere.
Finally, very recent results suggest that early Earth was an ocean world https://www.universetoday.com/145214/3-billion-years-ago-the-world-might-have-been-a-waterworld-with-no-continents-at-all/#comment-159746 ].
But Totani deviate from the consensus and thus consider us rare in the universe. Along that line of analysis, cosmologists think not since we discovered inflation. Eternal inflation, which is what we see, naturally makes infinite many universes, each with its own physics. Very few – roughly 1 out of 10^120 – are habitable since star or even atoms demand physics in a narrow range. That would (arguably) explain why our universe is good for producing life but also why it is bad at supporting it (long distances between stars and galaxies). A galaxy here or there with a planet here or there will have human analogs.
To be clear: that does not happen right now though, for reasons already Darwin found out, earlier life consuming cell building compounds as nutrients.
And that is what we see, all life derives from a universal common ancestor.
That underground (as in deep hydrothermal vents) once evolved life on Earth? That is currently the dominant hypothesis in the field.
I hear you. But on the other hand Totani is keeping with a minor tradition in the field, where probabilistic models and biologists that can't see how evolution would get around evolving its own genetic machinery has published similar papers for decades. E.g. even the merited Koonin once wrote on 'the biological big bang' of having enough planets to get an - according to him - minimal set of proteins doing it https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1973067/ ]. (He had the reverse problem, he did not appreciate the astrophysical side.)
https://www.nature.com/articles/nmicrobiol2016116 . Mind that just this week I saw that this often referred to paper met a criticism - I'm not fond of either work's methods and I don't see that either is conclusive in test, so I'll take the weak criticism as evidence that the work is not totally without merit (and nor is the criticism, of course).]
My observation, *which is what we see*. To get around a rare Earth and universe we live in today, cosmology uses inflation and multiverse doctrine. Reports I have show the multiverse could contain 1E+500 different universes, and now I see 1E+120 universes in the multiverse may be habitable. Okay folks, here was consensus cosmology thinking in 1948, a lesson from the past.
“Nineteen years after Edwin Hubble’s discovery that the galaxies seem to be running away from one another at fabulously high speeds, the picture presented by the expanding universe theory—which assumes that in its original state all matter was squeezed together in one solid mass of extremely high density and temperature—gives us the right conditions for building up all the known elements in the periodic system. According to calculations, the formation of elements must have started five minutes after the maximum compression of the universe. It was fully accomplished, in all essentials, about 10 minutes later.” —Scientific American, July 1948
Apparently the cosmology department underwent some serious new math development to work with new observations since 1948, but both use QM and GR to explain the expanding universe. At the moment, I am not aware that any telescope on Earth recorded and observed 1E+120, potential habitable universes with stars in them. The Big Bang model shows CMBR redshift where z >= 1000, thus the universe is limited to about 46 billion light years radius as cosmology calculators show, https://ned.ipac.caltech.edu/help/cosmology_calc.html, just plug in z=1000 and use the default settings for flat universe calculations.
Presently very remote objects have redshifts near 12.0 recorded by telescope spectra like GN-z11. Telescopes operating on Earth (or space) do not *see* what inflation claims in this discussion, i.e. there are other universes and stars that statistically according to multiverse thinking, could be habitable. Galileo argued against the geocentric astronomy using the telescope. Others using the telescope confirmed that the Galilean moons were there, and moved around Jupiter so supported what Galileo presented. I use my telescopes and can confirm that the Galilean moons are there and move around Jupiter today, some 400 years later. Presently we have confirmed 4255 exoplanets now, The Extrasolar Planets Encyclopaedia
No exoplanets on this list are documented showing life is there (presently). Telescopes do not show other universe that could be habitable with other stars too that could support life as we see here on Earth. This is what we do see today using science and the scientific method, rooted in observations, testing, and falsifying claims.