One longstanding theory is that life first began on Earth when asteroids carrying fundamental elements crashed into our planet long ago.
I'm no expert but this sounds strange. Surely those fundamental elements would also form in vast quantities on their own on an entire planet with volcanoes and oceans? Wouldn't a couple asteroids be the literal drop in the ocean in comparison?
The missing part is how do they form self-replicating mechanisms capable of evolution. I doubt an asteroid with a bit of organic dust is enough for that. If such small amounts suffice we should see the formation of new life forms from scratch, today, left and right I think?
The timing of the delivery is what's important here. These building blocks, organic matter, and water would have been depleted in the proto-Earth due to Solar irradiation. There needs to be some mechanism that delivers these ingredients from the outer Solar System. Bombardment by smaller rocks makes the most sense, and was likely triggered by the migration of Giant Planets, leading to a period of heavy bombardment (on a bare Earth -- no oceans, no volcanoes).. https://en.wikipedia.org/wiki/Nice_model
The smaller rocks are composed of those materials in solid state (e.g., ice not water). They are less irradiated as they are further away from the Sun (think the asteroid belt and beyond). Atmospheric entry (if that's what you mean) is irrelevant. What matters here is the transport of materials from a place where they could have formed, to a place where they couldn't.
Atmospheric entry is completely relevant because some people have made the illogical claim that meteorites falling on Earth could have contributed with such complex organic substances, like the nucleobases, to the appearance of life on Earth.
The icy bodies from the outer Solar System that contain such organic substances are very easily vaporized during entry in the atmosphere of the Earth, so only a negligible fraction, if any, of the organic substances originally present in such a body would reach the surface of the Earth.
Wouldn't a big enough asteroid have an inner part which survives entry? You seem to be saying that it's impossible for any meteorite that might have these chemicals to not be completely vaporized which seems doubtful. Have you got a source?
Most asteroids have slowed to terminal velocity by the time they impact. It’s not nothing, but it’s mostly going to be relevant to physical processes and not chemical ones.
You might consider that scientists advanced enough in their field to be launching missions to retrieve dust from asteroids are actually aware of basic facts relevant to their field of study.
You might consider that even concepts like plate tectonics (which frankly are incredibly obvious if one just looks at a map) were considered ridiculous ideas by the most advanced experts in their field at one point. A point not that long ago.
I’m not saying the person you are responding too is right - but appealing to authority on something like this has a pretty bad track record.
One theory is that the primitive Earth contained much smaller quantities of the volatile chemical H, C, N, O and S, which are the main constituents of water and of organic substances.
Then Earth collided with a great number of small bodies formed in the outer Solar System, which were rich in water and organic substances. This has modified the composition of the Earth towards the current composition. (Later Earth has lost a part of its hydrogen; because hydrogen is very light, it is lost continuously from the upper atmosphere, after water is dissociated by ultraviolet light; thus now the Earth has less water than around the appearance of life.)
This theory is likely to be true, so meteorites probably have brought a good part of the chemical elements most needed by living beings.
However, most of the pre-existing organic substances from meteorites must have decomposed and whatever has been preserved of them could not have had any significant role in the appearance of life here, because any living being would have needed a continuous supply with any molecules that it needed, otherwise it would have died immediately. Such a continuous supply could have been ensured only for molecules that were synthesized continuously in the local environment here, not for molecules arriving sporadically in meteorites and which would have been diluted afterwards over enormous areas, down to negligible concentrations.
> Atmospheric entry (if that's what you mean) is irrelevant.
I think the OP meant that Earths magnetic field and atmosphere shields any terrestrial matter far more than than a bare asteroid that has no such protections, so it seems implausible at first glance that these things would develop or survive in open space rather than here.
> it seems implausible at first glance that these things would develop or survive in open space rather than here.
I don't think "organics developed in the vacuum of space" is implied. Survived? Well we have samples now confirming, if I'm understanding the basis for the discussion (the article).
Causality was not the point. The point was to refute the seeding hypothesis, and because they found those molecules, the effort to falsify the hypothesis failed. Now we can move on to the next attempt to refute, which, as you say, might be to study whether molecules can survive conditions of reentry.
Experiments do not tell us that something IS a certain way; only the ways it is not.
The ideal situation for an expert is to prove causality!
It’s nearly impossible, but it is the holy grail!
This experiment was to try to falsify one theory, yes, but as you note that is a very long way from the actual goal - or the level of certainty that the article is trying to imply.
These articles are written due to funding needs, which is why the articles are the way they are - and why the scientists themselves are likely cringing too when they read these articles. At least until the checks (hopefully) arrive.
I was under the impression that the ejection of these compounds demonstrates that organics (blocks) can escape a gravity well, which implies they can likely re-enter another.
Those smaller rocks are in the outer solar system, where the solar irradiation is lower. But the way they are composed is lots of ices (volatile molecules in solid form) being built on the silicate/graphite refractory core. The ices remain preserved in the environment provided by the outer solar system.
Extra terrestrial propagation of life, if real would have evolved to have non-zero survival rates in interstellar radiation regimes and timescales.
The fragility of life-as-we-know-it that has undergone serial passage in an environment largely shielded from radiation, is not necessarily representative of putative life-forms carried by little rocks in space.
I am neither convinced for nor against the idea that life may have been carried over by interstellar rocks: on the one hand, its a major promiscuity between celestial bodies within star systems, galaxies, etc. on the other hand since we haven't discovered other life forms yet we have no idea on the missing probability densities of life in the bulk of the universe, so the Bayesian catapult can swing either way, we just lack the data for now.
Meteorites are generally cold when they reach the surface of the earth. The heat of reentry is very brief and generally just on the surface. That's my understanding.
The surfaces are typically melted - the ones that don’t just explode anyway.
Icy meteorites never survive re-entry that I’m aware of; and most carbon/chondrite ones don’t either, but they are the most common type that do. They tend to be ‘dry’, however.
Praying[0] is a good start! That, coupled with large amounts of suspension of disbelief[1] helps too.
I suggest drinking (or whatever your preferred brain-fogger might be) heavily. That helps you ignore the details -- because the "devil is in the details" and we mustn't have that, right?
[0] Also known as "begging an imaginary sky daddy for help"
I realize you're just replying in kind to the GP, who wasn't very nice himself. I also think it's not necessary to feed such trolls in a way that insults all the religious folks who do enjoy this site and don't try to push our faith on others.
It's okay. I appreciate the cover, but it's important to let this oppressed, hunted, hated and endangered group have their say.
There is, after all, a war on Christmas, Christians and Christianity.
Christian enclaves are being attacked and Christians are being murdered in the thousands every week, just for being Christian.
Hundreds of decent, god-fearing Christian women are being raped daily by strong, manly Muslim men. Their strong muscles rippling under their tight clothes, stirring up strong, lustful feelings among the faithful Christian men.
It's no wonder that folks are kind of touchy. If you risked being shot, blown up, cuckolded or otherwise made dead or humiliated every time you went to a church, made the sign of the cross or put a "Jesus is my Co-pilot" bumper sticker on your vehicle, you'd be concerned wouldn't you?
And that happens every day because people hate them for their knowledge of the truth. It's all there in the literal word of god that's in the Holy Bible. Anything else is heresy. And we know what to do with heretics, don't we?
I guess it depends on how you define life, and whether we'd even recognize it when we see it, assuming we're looking in the right places.
I'd also imagine that any type of chemistry that harvests energy from the environment is liable to find itself as a food source at the bottom of the food chain now that earth is teeming with life.
I think that self-replication, and ability to harvest chemicals and energy from the environment to make more of what you're built of, is the point of complexification of chemistry that is best considered as the most primitive form of life. From there you can go on to things that are capable of encoding structure and more complex chemical factories.
I suppose one signature of these earliest type of "emergent life" chemistries would be localized concentrations of things like these nucleobases that we know are the building blocks of life as we know it, but there may be other types of self-replicating chemistries that emerge too, that don't lead anywhere.
> I think that self-replication, and ability to harvest chemicals and energy from the environment to make more of what you're built of, is the point of complexification of chemistry that is best considered as the most primitive form of life
Once there are forms that harvest and self-replicate, however, its expectable that there will be forms that delegate those features to others, like viruses. Cellular machinery that is required to implement those feature is not free, so parasitic forms would have survival advantage.
He's an interesting person overall - the long interview is well worth watching if you haven't already seen it - but the relevance here are his experiments with the emergence of self-replicating computer programs out of random components.
His starting point is entire "programs" (random sequences of 64 characters, of which only ~7 have any meaning - the program "statements" of the BF language), so perhaps more suggestive of this RNA world stage, but perhaps also of what came before it when there may have been collectively self-replicating soups consisting of discrete components rather then entire structural encodings.
Parts of the RNA world theory are correct, but other parts are completely bogus and completely illogical.
What is correct is that RNA must have existed a very long time before DNA, during which RNA was the only nucleic acid.
Moreover, self-replicating RNA must have existed before ribosomes and proteins (where "protein" means a polypeptide that is synthesized using a RNA template).
It should be obvious that neither ribosomes nor protein-encoding RNA-sequences may exist before the existence of self-replicating RNA, because the living being in which those would exist would immediately die without descendants, together with its content of ribosomes and proteins.
So far so good, but some of the supporters of the RNA World theory claim that before the existence of protein-based enzymes, all chemical reactions inside a living being must have been catalyzed by RNA molecules.
This is an illogical claim, which is false beyond any reasonable doubt. Some RNA-based catalysts may have existed quite early, and some still exist today. However, any RNA-based catalyst could have appeared only at a later time after the establishment of RNA self-replication. The argument is the same as for protein-based catalysts, any living being with a RNA catalyst, but without RNA replication would die and the RNA catalyst would disappear without descendants.
So there is no doubt that the first feature of RNA that has appeared was self-replication, and at that time RNA could not have any other role inside a living being, because any such role would not have been inherited.
In other words, the first self-replicating RNA molecules were a kind of RNA virus, which multiplied inside the existing living beings, consuming energy and substances, without providing benefits. Only later, when eventually RNA templates have become the main method for synthesizing the useful components of a living being, something akin to a symbiosis between RNA and the rest of the living being was achieved, arriving to the structure of life that is known today.
For the first self-replicating RNA molecule to appear, the living beings must have contained abundant ATP and the other nucleotides. So the original role of the nucleobases in living beings was not the storage of information, but the storage of the energy required for synthesizing organic polymers. The self-polimerization of the nucleotides, which forms RNA, was an unwanted side reaction. In other words, before the RNA world, there already was an ATP world, which was the first user of nucleobases.
If RNA could not have been the material for making enzymes before the proteins, such enzymes must have been made from peptides (i.e. polymers of amino-acids), exactly like the enzymes of today, but those peptides must have not been synthesized using ribosomes, like the proteins. Such peptides still exist today and they remain widespread in all living beings, and they are named non-ribosomal peptides. Their mechanisms of synthesis are much less understood than the mechanisms of RNA-based protein synthesis. It is likely that more research into non-ribosomal peptides might provide a better understanding of how a living being without RNA could function.
In order to have a self-replicating living being you do not need a self-replicating molecule able to store arbitrary information, like RNA. It is enough to have a chain of synthesis reactions that closes a positive-feedback cycle, i.e. the products of one reaction are reactants for the next reaction and the products of the last reaction are the reactants for the first. If the chain of reactions produces all the components of a living being, growth and self-replication can be achieved.
The defect of such a living being is that evolution is extremely difficult. any mutation in one of the catalysts used in the chain of reactions is more likely to break the positive feedback and lead to death, instead of producing an improved living being. After the appearance of memory molecules, i.e. RNA and later DNA, which can store the recipe for making an arbitrary polymer molecule, it became possible to explore by mutations a much greater space of solutions, leading to a greatly accelerated evolution of the living beings.
I read a few times your comment and I went from "Nah" to "It makes a lot of sense". I'm adding the "ATP word" to my list of interesting ideas.
Some related stuff:
* https://www.science.org/doi/10.1126/science.adt2760 They made RNA that copies itself, but it use as a starting point activated triplets of bases. i.e, if ATP is AR-PPP, they use a mix of something compounds like AR-P-AR-P-AR-PPP that stil have the triphosphate to store energy and be easy to link, but already have tree linked bases. This is even more difficult that a soup of ATP and friends.
* https://en.wikipedia.org/wiki/PAH_world_hypothesis The idea is that before the RNA word, there was something simpler, like this. Is it possible to use ATP to build more PAH? I also remember about a version of RNA that instead of ribose it used something smaller (glicerol?), but I can't find it.
>However, any RNA-based catalyst could have appeared only at a later time after the establishment of RNA self-replication.
RNA by virtue of its biochemistry is capable of self replication already. Sequence affinity alone is sufficient to drive structure formation. But without a template, structure can also form on its own (example of an open access paper exploring one such mechanism under certain conditions, 1).
RNA is not capable of self replication. RNA by virtue of its biochemistry is only capable to be used as a template for replication, but the copying of the template must be done by a different molecular machinery.
If you put almost any RNA molecule in a jar together with monomers, you can wait until the end of time to see its replication.
Normally, RNA can be replicated only by a special enzyme, a RNA-dependent RNA polymerase. This kind of protein is used by many viruses.
It is hypothesized that a RNA molecule with a very special structure might have been used in the beginning as the catalyst for template-controlled polymerization, instead of a RNA-dependent RNA polymerase, to ensure self-replication. Some experiments have suggested that this is indeed possible.
Only after a self-replicating RNA molecule already existed, or if a RNA molecule existed in combination with a RNA polymerase that was produced by other means than by using a RNA template, other RNA molecules with various other functions could appear, and they would have been replicated by the already existing mechanisms, so they would be inherited by the descendants of a living being.
The link provided by you has nothing to do with RNA replication.
It describes a mechanism for the polymerization of nucleotides, which produces random nucleic acid molecules, not molecules that replicate an existing template.
A chemical reaction of this kind is what must have existed before the appearance of a self-replicating RNA molecule. Among the many random polymers produced before that, there was eventually one capable of self-replication, which started the evolution of genetic information.
This kind of reaction is what I have referred to as "side reactions" that happened during the use of ATP and of the other nucleotides as energy sources for the polycondensation reactions used in living beings to make macromolecules.
> RNA is not capable of self replication. RNA by virtue of its biochemistry is only capable to be used as a template for replication
RNA molecules which can synthesize others have been produced in a lab.[1,2] Your claim is not only totally unsupported, it's been experimentally disproven.
Laboratory RNA production can be done with regular batch chemistry - no enzymes involved, so on a long enough time span heat and mixing would be able to polymerase candidates out of the primordial soup.
RNA self-affinity is well documented, double-stranded RNA viruses exist[2] so stable conformational arrangements of RNA are not only experimentally proven but so viable they exist in todays much more enzymatically hostile world.
The relative difficulty of the structure persisting is a point in favor it is as a replication medium, since if RNA could tightly bind RNA then templating new strands would inactivate it.
You sound awfully confident about this, given we have no direct evidence for most of your claims. I would find your writing more convincing if you didn't make absolute statements.
This theory is called panspermia [1] and it has several alternatives. One of the most extreme is that in the very early Universe, these building blocks could spread easily because the ambient temperature of the Universe was significantly higher than it is now. This isn't the most popular version.
The most popular is that asteroids and other interstellar bodies spread the building blocks, be it anywhere from amino acids to more complex building blocks. As evidence of this, there are hundreds of surviving asteroids on Earth that have been positively identified as having coming from Mars, which is pretty crazy because that basically takes a violent impact throwing debris into space and it making it to us many times over.
Part of the evidence for all this is how soon after the Earth formed that life appeared. We have positive evidence that this only took a few hundred million years. That's kinda crazy if you think about it. Also consider that the oceans likely came after the EArth formed.
Our galaxy is over 10 billion years old. The Sun is less than 5 billion years old. So that's 5+ billion years for stars and Solar Systems to form, evolve and die before the first fusion reaction in the Sun. Some of this needed to happen just to form heavy elements that are relatively abundant. Even that's kind of crazy. Heavy elements like lead, uranium and gold take relatively rare and violent events to eject material into space and make it to us. So what else made it to us?
Paints the picture of an early solar system that was a fairly connected system. Perhaps life didn’t form anywhere but Porto-life formed everywhere and earth is the only place that hasn’t died yet
1 - Abiogenesis is incredibly rare. We don't know how much exactly, but it's a lot.
2 - Abiogenesis happened on Earth about as soon as it became possible. Where "as soon as" means within half a billion years, but it's still way quicker than its rarity implies.
A lot of people think panspermia is what made those two happen. Life had about a full billion years to appear in meteors before they could appear here.
There are some problems, e.g. that each meteor only stayed chemically active for less than that half-a-billion years Earth had. Or that all the meteors that fell on Earth had only a fraction of the material that was later available here. But IMO, the largest issue is that just doubling the time is absolutely unsatisfying.
Life cannot appear in any of the small bodies that become meteors, because there is no source of energy for it.
Life can appear only on big planets or on big satellites, like the big satellites of Jupiter and Saturn, if they have a hot interior and volcanism.
Volcanism brings at the surface substances that are in chemical equilibrium at the high temperatures of the interior, but which are no longer at chemical equilibrium at the low temperatures of the surface, providing chemical energy that can be used to synthesize macromolecules.
Solar energy cannot be used for the appearance of life. Capturing light requires very complex structures that can be developed only after a very long evolution and which cannot form spontaneously in the absence of already existing living beings.
The only theory of panspermia that is somewhat plausible is that life could have appeared on Mars, which had habitable conditions earlier than Earth. Then, some impacts on Mars have ejected fragments that have fallen as meteorites on Earth and some remote ancestors of bacteria have survived this interplanetary trip.
There are many meteorites on Earth that have their origin in impacts from Mars, so at least this part is known as being possible.
>Solar energy cannot be used for the appearance of life. Capturing light requires very complex structures that can be developed only after a very long evolution and which cannot form spontaneously in the absence of already existing living beings.
I think that is putting the cart well before the horse. Earliest "life" I would say looks something like a short sequence of random RNA, in some structure (as in secondary), in some solution, among some nucleotides, where brownian motion lead to collision with nucleotides in the chain that grow the chain and/or template off the chain and make a copy. The energy requirements for this sort of pre cell life are far less than cell based life which has to spend energy on cell membrane or wall building. Energy could be quite low, it would just reduce the number of interactions over time. Likely also that this pre cell "life" would not die either so long as it is protected somewhat by cosmic radiation bombarding the chain (although to an extent this is also a ripe source of mutagenic potential).
No kind of life can exist without a continuous flux of energy. The formation of any organic polymers requires energy, it cannot happen spontaneously.
Nucleotides that collide do not form polymers in water. The polymerization of nucleotides and of amino-acids and of most other organic macromolecules is done by water extraction (a.k.a. polycondensation).
Water extraction inside water requires considerable energy (i.e. you must dry some thing while it is still submerged in water). This is provided by certain dehydrated molecules, like ATP, from which water must have been extracted as a result of capturing some energy from the environment.
The common ancestor of all living beings known on Earth obtained energy by the reaction between free hydrogen (dihydrogen) and either carbon monoxide or carbon dioxide. It is likely that the capability to use carbon dioxide has appeared later and the very first living beings were powered by the conversion of dihydrogen and carbon monoxide into acetic acid. The energy from this reaction was captured because the first result of the reaction was not free acetic acid, but acetic acid condensed with another molecule, like in the acetyl-CoA that is used today by all living beings. Than that condensed molecule could be used to extract water from other molecules, producing dehydrated molecules like ATP, which can be used for the polymerization of nucleic acids.
There is no way to circumvent the need for a continuous source of energy for the appearance of life. Besides the H2 and CO gases, there was an alternative source of energy that was used very early, but it is not known if it was already needed for the initial appearance of life or it began to be harvested at a later stage. This second source of energy is the difference in ionic concentration between the acidic water of the primitive ocean and the alkaline water that is produced by dissolving volcanic rocks in places like hydrothermal vents, where H2 and other gases are also produced. The ionic concentration gradients produce ionic currents, which can power certain chemical reactions, like they also do in all present living beings.
Asteroids early in the solar system would be very radioactive due to short lived isotopes formed during the formation of the solar system. The existence of these isotopes is known from the patterns of decay products found in asteroids. The current guess is the early protoplanetary disk was bombarded by intense GeV-scale protons accelerated in the shock of a nearby supernova, causing large scale transmutation in the disk.
There is no known way in which nuclear radiation could have been the source of energy for the first living beings.
While a little radiation might have been beneficial at a later stage in the evolution of living beings, by increasing the frequency of random mutations, for a faster evolution, for the early living beings the only effect of radiation would have been to destroy them and prevent them for having descendants.
The only positive effect of the increased radioactivity in the early Solar System is that it is possible that not only the planets but also some smaller asteroids might have had warm interiors and volcanism.
So in none of the huge number of small bodies that exist in the Solar System there have ever been conditions for the appearance of life, but perhaps on some of the bigger asteroids there might have been such conditions, if they also had water and volatile chemical elements, besides a warm interior.
If life has ever appeared in such a place it must have used the same sources of energy that are known to have been used by the ancestors of life on Earth, i.e. gases and ionic gradients produced by chemical reactions between water and volcanic rocks.
There not only there was no known source of energy for the synthesis of organic polymers, but also everything, with the exception of interstellar dust particles, was in a gaseous state, not suitable for forming the structure of a living being.
It appears all the "disk" labels are categorical. The concept I'm trying to find the name for is the continuous, slow, asymptotic reduction in the number of disjoint particles/collections spinning around a star. All the relevant "disk" labels would probably be all those on the right side of this curve, where water is present.
I would think the Sun, with its photons and charged particles, and the various electrostatics (like triboelectric) involved, would be the energy source. The disk starts, somewhat evenly distributed, with a whole annulus of surfaces in the Goldilockz zone, with water, etc present. Through time, these bounce off one another, eject bits, stick on others, preserve bits in ice, etc, smearing/spreading whatever allowed their synthesis.
Looks like this maybe has merit, with organic molecules found [1].
People make the inference that "early occurence of life" implies "life must be easy to start". But that inference requires the assumption that the chance of OoL (origin of life) remains mostly constant with time. An alternative would be that the conditions under which life could arise are transient, so life either starts early or not at all. We don't know enough about OoL to rule this out. Some chemicals that might be needed for OoL, like ammonia, are not stable for long. And if life originated in small asteroids, this might have only a few million years for it to occur while they are still warm enough from early short lived radioisotopes like Al-26.
It is indeed possible that in the early Solar System, before the short-lived radioactive elements completely decayed, there were some asteroids with good conditions for the appearance of life.
However, I would not describe those as small. The majority of the interplanetary bodies that orbit the Sun and which fall from time to time on Earth as meteorites are far too small to have ever had conditions for the appearance of life.
Even an asteroid like that which has wiped out the dinosaurs, with a diameter of a few km could not ever have suitable conditions.
Only relatively large asteroids, presumably with diameters from tens of km to hundreds of km, might have had warm interiors and volcanism for enough time to allow the appearance of life.
Such asteroids must also have been among those distant from the Sun, in order to contain enough water and volatile chemical elements.
The fact that the most volatile chemical elements are those most important for life is not due to chance, but due to the necessity. The volatile elements are those prone to forming covalent chemical bonds. Unlike the metallic or the ionic chemical bonds, the covalent bonds are strictly required for forming the complex molecular structures that may lead to living beings.
> However, I would not describe those as small. The majority of the interplanetary bodies that orbit the Sun and which fall from time to time on Earth as meteorites are far too small to have ever had conditions for the appearance of life.
So what? The meteorites that fall to Earth were not that size for their entire existence. They are fragments of larger bodies that have collided over the billions of years. Iron meteorites, for example, are remnants of the cores of larger bodies that were big enough to undergo melting and differentiation in the early solar system.
Moreover, "not all places are suitable for OoL, therefore no places are suitable for OoL" would be a non sequitur, so I don't see how what you're trying to say there leads anywhere useful.
If earth is about 4 billion years old, but it takes say 400 trillion years for natural processes to produce this chemistry, then it happened out there not here.
This was a key reason why Hoyle preferred a steady state model of the universe — the part of the universe we inhabit needs to be very, very old for this stuff to work out, according to his thinking. A minority opinion, for sure, his rejection of the Big Bang model and timelines lost him a lot of respect among his peers. And his ideas could be wrong, I’m just pointing out that historically panspermia proponents have taken this position as to “why not here”.
Admittedly, am layman, have only heard numerous sciencey folks talk about it, but we've found all these basic components in space already, naturally occurring, and while we've never to my knowledge recreated actual, genuine abiogenesis, we have observed every process required for abiogenesis to be a reasonable explanation for the origin of life.
As to your question on we should see the formation of new life everywhere, well, if we looked hard enough we might? The answer is competitive exclusion. Abiogenesis would've occurred on a remarkably clean earth: any life now emerging from the proverbial space dust is both almost certainly not preconfigured for this biosphere, and is instantly drowning in competing microorganisms that are. Anything that does form is likely quickly killed either by natural forces or competing organisms. Meanwhile, our life goes everywhere: We've found living bacteria on the outside of the ISS!
> Wouldn't a couple asteroids be the literal drop in the ocean in comparison?
Actually most water on earth probably came from asteroids, so they are the entire ocean! They would also have brought a lot of frozen methane and ammonia, so most of the chemicals necessary for terrestial life.
When the solar system was forming, the protoplanetary ring of cosmic dust would have consisted of heavy elements (some essential for life, such as phosphorus) closer to the sun and frozen lighter elements further away. The heavy elements would have combined into the early rocky earth, and as the other planets formed and orbits stabilized the icy asteroids from further out would have been flung around and impacted the planets.
My layman guess would be that shortly after formation Earth was just a ball of lava that destroyed every organic component so when the surface solidified it was sterile.
Yep, you are 100% correct. In fact, it is much more likely they were originating on Earth itself than a random hobo asteroid.
> The missing part is how do they form self-replicating mechanisms capable of evolution.
Well, there are some missing parts, yes, but RNA can self-replicate already; at the least some RNA can. Ribosomes also contain RNA so its is a ribozyme.
That's not replication, that's polymerization. There's nothing template-directed about it, and as far as I can tell the experiment depends on pure initial conditions (the guanosine monophosphate is not mixed with a plethora of other chemicals that could copolymerize with it.)
That purity is the kind of artificiality I was talking about. A bad habit of OoL research is to show that some chemical shows up in trace amounts, then starting the next stage of experiments with a pure batch of that chemical. Robert Shapiro in his 1986 book "Origins" had some very biting things to say about this (the book is not nice to creationists either, btw.)
Again, implausible purity there. I'll add the tetramers used as the components are also much larger than the nucleotides in the Ryugu paper, so would be present in much lower concentrations.
I agree. If we knew the mechanism for how life started we'd probably be doing the experiments to prove it. There are theories and experiments that suggest some life-like processes can happen with inorganic compounds, but they require a lot of squinting and a bit of imagination to connect with our own origins. And there's a big difference between experiment and nature. On the one hand, we have people trying to make it happen, while on the other hand, it apparently already happened once, without anyone even needing to be around.
Which is underplaying what "trying" means in this context: we live on a planet with a lot of life - life which by definition was a superior competitor to the much simpler life it supplanted. The world, even enzymes from our skin, are unimaginably hostile to most candidates for simpler primordial lifeforms.
The reason showing abiogenesis is hard is because (1) everything in the biosphere would kill and eat the result and (2) the one thing it had going for it was time - millions of years of random diffusion with nothing else busy executing a grey goo type attack on all the available resources.
Frankly if someone gets abiogenesis to work in a lab environment within a single human lifetime, it wouldn't just be evidence for how it might've happened in Earth's past it would more or less set the parameters for how much life there must be in the universe everywhere because a mere 50 to 100 years to kickstart anything would be insane.
> One longstanding theory is that life first began on Earth when asteroids carrying fundamental elements crashed into our planet long ago.
That theory is bullocks. When an asteroid enters the atmosphere and crashes as high speed on the surface, you get a huge amount of energy that creates an explosion and a destruction of most complex chemical material in the process. It's no mistake that these kind of impacts are counted in the same range as multiple atomic or hydrogen bombs.
Comets is where many astronomers have long thought the ocean came from. Comets are literal drops in our ocean. LOTS of comets. The atmosphere and the Earth at large would have been very different, and being bombarded by many giant space snowballs (along with asteroids) would have contributed materials. The missing part is, um, missing. We still do not know. However, these samples contained building blocks, not actual self-replicating RNA. That might seem like nothing, but before this discovery, we thought they only contained one ingredient.
That is not about the replication or self-replication of RNA.
The article is about a mechanism that may produce random nucleic acid molecules, i.e. molecules that do not replicate any template.
Reactions of this kind, producing random nucleic acids, must have existed long before the appearance of the first self-replicating RNA, thus before the appearance of any nucleic acid that could be inherited by the descendants of a living being and that could provide any useful feature for that living being.
I don't think you'd want a single homogeneous "large pool", but rather a large variety of different types of micro-environment, including all those that have been suggested as possible environments for the emergence of life - the chemical and physical environments of hydrothermal vents, volcanic hot springs, shorelines, different types of rocks, clays, etc. You'd want to have environments that included all energy sources present on earth (solar, lightening, geothermal), all forms of mechanical agitation/mixing (hydrothermal, waves), etc, etc.
The bigger the pool the harder to create it here on Earth without introducing problems. For example, take a prion. Hard as hell to actually get rid of, how do you know you've not actually introduced something like this to your sterile pool that's going to make it do things you don't expect.
Yeah, but it seems impossible to experiment on the scale that would have happened in nature where there would have been millions of localized "test tube experiments" ongoing for millions of years.
Of course people can, and do, try to replicate early earth environments and self-assembling proto-cells, but I'm not sure how intellectually satisfying any self-replication success from these "designer experiments" would be, unless perhaps done on such a large scale (simulation vs test tube?) that any conclusions could be made about what likely happened in nature - just how specific do the conditions need to be?
My personal theory is that the conditions for life are plentiful in the universe but it probably took an unbelieavable number of random chemical/mechanical events to form the first proto-lifeform.
The discovery comes after these building blocks of life were detected on another asteroid called Bennu, suggesting they are abundant throughout the solar system.
We've barely started to look, other than on Mars, and notably we are seeing possible signs there. There may even still be primitive life there.
If we do find life of Mars, or say Europa, i.e. in the very first places we look for it, that that would be highly suggestive that it is extremely common (at least in primitive form).
Also it seems that finding a balance where an ecosystem doesn’t kill itself with its own waste is probably harder than we assume. Earth life has totally changed the atmosphere of the planet, I would many it many cases even when life does for it kills itself early on
Surely in a minority, but I do see posts from people on HN that are scientists, researchers, even mechanics and such. We definitely get a lot of speculation, but I've learned never to underestimate the level of expertise of people in our community.
The missing part has been conducted in other experiments. I don’t have time to give you some papers, but nucleic acids can self assemble into long chains under the right condutions. No polymerase enzyme is needed.
> The frequency of an asteroid impact on Earth is ~500,000 years.
Surely you could make this figure be anything you want just by scaling up or down the size of an object you call an asteroid. So as stated it's meaningless.
A cynic might suggest the theory might exist because nobody could figure out how life got started on its own on earth.
The thing is I've never found the asteroid theory particularly satisfying either because it simply inserts another abstraction layer, explaining the problem away rather than explaining it.
That's not to say it's wrong but, in its current incarnation, it's just a bit meh.
I suppose perhaps that's part and parcel of it being a very hard problem to solve.
There are 2 distinct kinds of claims made about the role of meteorites fallen on Earth whose origin is in such bodies like the Ryugu asteroid.
One claim, which is likely to be true, is that in the beginning the Earth had a lower content of volatile elements, e.g. hydrogen, nitrogen, carbon, oxygen and sulfur, than today. The reason is that Earth has condensed at a high temperature, being close to the Sun, and those elements would not have condensed.
Later, the Earth has been bombarded by a great number of asteroids formed far from the Sun, which were much richer in H, C, N, O and S, and this bombardment has provided a major part of the chemical elements required for water and for organic substances.
A second, different claim, which is almost certainly false, is that this bombardment of the Earth has provided not only the raw chemical elements, but also pre-synthesized organic substances, like amino-acids and nucleobases, which have taken part directly in the origin of life.
This second claim does not make sense. The meteorites rich in water and organic substances are extremely easily vaporized during atmospheric entry or during the impact with the surface and their content of organic substances would decompose.
Even if we suppose that some falling bodies were so big that parts of them survived until the surface, any organic substances thus brought on Earth could not help in any way the appearance of life.
Any form of life would need a continuous supply of such substances, otherwise immediately after consuming the few molecules adjacent to it the life form would die without descendants.
Life can appear only in a place where there is a continuous supply of energy and it can use only chemical substances that are continuously synthesized in abiotic conditions. It cannot appear based on sporadic events, like the fall of a meteorite, which would also destroy anything at its place of impact.
Such places where energy is available continuously and there are also the substances from which complex organic substances can be synthesized through catalysis by various minerals, mostly metallic sulfides, exist both on Earth and in other places in the Solar System. These are the places where either volcanic gases are released or similar gases are produced by the reaction of water with volcanic rocks, in hydrothermal vents. As far as we know, those are the places where life must have appeared, because all the necessary ingredients exist. The only mysterious part is how it has happened that a correct combination of the mineral catalysts required to synthesize all the needed organic molecules happened to be located in close proximity and in the right sequence.
Today, even if such places still exist on Earth, life could not appear again. First, the oxygen from air would destroy any substances thus formed, and even where oxygen is missing the ubiquitous bacteria would consume any organic substances that could form abiotically, preventing their accumulation and the formation of any kind of structure from them.
> This second claim does not make sense. The meteorites rich in water and organic substances are extremely easily vaporized during atmospheric entry or during the impact with the surface and their content of organic substances would decompose.
Such meteorites fall to Earth even today. Their interiors are often ice cold.
I'm in the middle of reading Peter Brannen's The Story of CO2 Is the Story of Everything—it's excellent and goes deep into the (bio)geochemistry of Earth—and he presents a good case for a metabolism-first development of life, taking advantage of "a disequilibrium that needed to be relieved at the vents, an unending stream d free energy to dissipate," rather than the RNA information-first theories.
It fits his overall narrative but it was an interesting way to think about life "as a thermodynamically necessary mechanism to relieve the continuous production of free geochemical energy on Earth... more efficiently than abiotic processes could." (Brannen quoting complex-systems scientist Anne-Marie Grisogono) I highly recommend the book.
This is similar to Nick Lane's books, and the research he references as well. The necessity for disequilibrium, the emphasis on life as the movement of energy across a barrier, etc.
I'm no expert but it seems most reasonable to me. The continual talk about pre-biotic soups of ingredients seems profoundly misplaced.
It contains nucleobases. But does it contain ribose, or ribose linked to the nucleobases, or to phosphates? And more generally, does it also contain a grab bag of related chemicals that are not building blocks? The existence of such blocks as minor constituents of a soup of random chemicals doesn't mean much, especially as the concentration of any such constituent declines exponentially with its complexity.
All it means is you can say "if life is rare, it's not because these specific small chemicals can't be produced". Which is a rather weak thing to say. It doesn't imply life isn't rare, or that further advancement the existence of these small building blocks is easy or inevitable.
I also asked about other things you have conveniently forgotten to mention there.
The overarching falsehood is that identification of biologically relevant molecules at 200 ppb levels, in a soup of tens of thousands of other chemicals, moves the needle any in figuring out OoL.
It's a sample of one, but I think the takeaway is just that if the nucleobases are present on a random asteroid then they probably commonly occur. Of course as you note it takes a lot more than that to form these into nucleic acids.
I would guess there is a more primitive stage in the emergence of life where self-replicating soups (Kaufmann: metabolisms), including things like nucleobases and amino acids, capable of collective replication/expansion exist, before we get anything as sophisticated as nucleic acids and structural encoding.
I wonder how they prevent contamination of the containers used to collect and store samples.
I assume they have to be ultra clean in every sense of the word 'clean' with the cavity pulled to a vacuum. And also the equipment that collects the sample and puts it into the canister has to be clean as well.
> Researchers from Imperial College London have discovered that a space-returned sample from asteroid Ryugu was rapidly colonized by terrestrial microorganisms, even under stringent contamination control measures.
> As described in the discussion of the journal paper, all samples received from JAXA have undergone the initial description, storage, and sealing in dedicated containers under a nitrogen atmosphere. The samples are distributed to researchers without exposure to the Earth's atmosphere. The possibility of microbial contamination is therefore considered extremely low. In addition, organic and microbial contamination assessment of the environment at the curation facilities within JAXA (clean chamber) in which the Ryugu sample grains undergo the initial description are conducted 1 ~ 2 times a year. It has been confirmed and reported that the concentration of organic matter is at or below the same level as that of the OSIRIS-REx asteroid return sample glove box at the NASA Johnson Space Center, and that no microbial colonies have been detected in the microbial contamination assessment conducted with swabbing and culture medium (Yada et al., 2023). Based on these facts, we agree that the microbial contamination described in the paper did not occur during a process within JAXA, but under the laboratory environment of the allocated researchers.
Please don't just post slop anyone else could have gotten from AI. It undermines the entire purpose of this site, and reduces the quality of discourse drastically.
Ummm ... the "Victoria University of Wellington in Australia"? Please. Victoria University is located in Wellington, New Zealand [1]. Nothing to do with Australia. Dr. Morgan Cable is a Senior Lecturer in Space Science at Te Herenga Waka, Victoria University of Wellington in New Zealand [2]. Can't believe that phys.org would publish such an error.
That's not really new. It seems as if some people try to project "there is life outside of planet Earth". Well, the thing is ... is this question important? You already have life here. Synthetic biology will also progress. So why is it important if life is anywhere else? I don't understand it.
There is nothing magic in RNA or DNA. Granted, right now we can not easily explain how life gets "bootstrapped", but recently there was a paper of self-propagating RNA even of a kind of semi-random sequence; this RNA can just amplify itself. I am sure you can find many more similar examples eventually as well as biochemical reaction processes that can be "bootstrapped" - and I am also sure none of these work on an asteroid. So why is there this strange focus on "life outside of planet Earth"? Some people want research money, that is clear now.
> It seems as if some people try to project "there is life outside of planet Earth". Well, the thing is ... is this question important? You already have life here.
How common the building blocks of life are out in the universe has important implications for open questions like the intersection of the Drake Equation and the Fermi paradox which has likely relevance to our own future here on Earth.
...though I happen to think what we know so far isn't comforting in the sense that the building blocks of life do appear to be very common and the most likely reason that we have to ask "Where is everybody?" in spite of that is that the Great Filter is probably expansionist self-destruction of the sort we are currently speed-running as a society.
The most important question we all want answered is just how rare life is in the Universe.
The fact that the building blocks are there just floating around on asteroids makes it that much more likely that its quite common.
If you look at the paper, the nucleobases were present at concentrations of about 1 nanomole per gram. So, maybe 200 ppb by mass for each. They are in a sea of other random organic stuff that is at best tangentially relevant to life as we know it.
I’ve wondered before if the idea that life originated on Earth might be the last geocentrism to fall.
Speculation of course, but it would fit a certain historical pattern.
Maybe life is all over the damn place, just a thing that happens under certain thermodynamic constraints, and it arrived on board comets or some similar mechanism.
Maybe space contains spores of minimal super simple organisms that can survive being vacuum freeze dried for incredibly long periods of time. When they land somewhere suitable they do stuff.
Maybe life originated long, long ago. The wildest speculation I have is that it originated shortly after the big bang during a brief period when the temperature of the universe was temperate, but that’s very far fetched for numerous reasons. More likely that it pops up from time to time and spreads over cosmic time scales.
But it only evolves to high levels of complexity in environments that are very friendly to a lot of life, have abundant energy, and are stable enough for a very long time. That may be the rare thing.
A asteroid has to be absolutely huge to make it all the way down to the surface without slowing down to terminal velocity. Your typical 1kg asteroid will have slowed to terminal velocity dozens of km above the surface. The smaller an object the lower the ratio of its mass to surface area and the more easily it slows down.
From near the start of the article: "In 2014, the Japanese spacecraft Hayabusa-2 blasted off on a 300-million-kilometer (185-million-mile) mission to land on Ryugu, a 900-meter-wide (2,950-feet-wide) asteroid. It successfully managed to collect two samples of rocks weighing 5.4 grams (under a fifth of an ounce) each and bring them back to Earth in 2020."
Surface sample:
Hayabusa2's sampling device is based on Hayabusa's. The first surface sample retrieval was conducted on 21 February 2019, which began with the spacecraft's descent, approaching the surface of the asteroid. When the sampler horn attached to Hayabusa2's underside touched the surface, a 5 g (0.18 oz) tantalum projectile (bullet) was fired at 300 m/s (980 ft/s) into the surface.[72] The resulting ejected materials were collected by a "catcher" at the top of the horn, which the ejecta reached under their own momentum under microgravity conditions.
Sub-Surface Sample:
The sub-surface sample collection required an impactor to create a crater in order to retrieve material under the surface, not subjected to space weathering. This required removing a large volume of surface material with a powerful impactor. For this purpose, Hayabusa2 deployed on 5 April 2019 a free-flying gun with one "bullet", called the Small Carry-on Impactor (SCI); the system contained a 2.5 kg (5.5 lb) copper projectile, shot onto the surface with an explosive propellant charge. Following SCI deployment, Hayabusa2 also left behind a deployable camera (DCAM3)[Note 1] to observe and map the precise location of the SCI impact, while the orbiter maneuvered to the far side of the asteroid to avoid being hit by debris from the impact.
It was expected that the SCI deployment would induce seismic shaking of the asteroid, a process considered important in the resurfacing of small airless bodies. However, post-impact images from the spacecraft revealed that little shaking had occurred, indicating the asteroid was significantly less cohesive than was expected.[76]
Duration: 36 seconds.0:36
The touchdown on and sampling of Ryugu on 11 July
Approximately 40 minutes after separation, when the spacecraft was at a safe distance, the impactor was fired into the asteroid surface by detonating a 4.5 kg (9.9 lb) shaped charge of plasticized HMX for acceleration.[56][77] The copper impactor was shot onto the surface from an altitude of about 500 m (1,600 ft) and it excavated a crater of about 10 m (33 ft) in diameter, exposing pristine material.[15][32] The next step was the deployment on 4 June 2019 of a reflective target marker in the area near the crater to assist with navigation and descent.[33] The touchdown and sampling took place on 11 July 2019.[34]
Or like some ancient alien species that travelled the stars but found it was alone, like in the ST:TNG episode[0]? No too.
Even if these ancient aliens thought it would be fun to spread their sperm all over asteroids and fling them out into the universe, there wouldn't be enough time for those rocks to get anywhere.
The more logical conclusion is that abiogenesis happens everywhere in the universe under the right conditions.
So what?! This does not prove anything! There are stones all around us, but they don't assemble themselves into beautiful, majestic stone buildings! All ingredients of concrete are around us, but we don't see them turning into concrete and pouring themselves into freeways, bridges, and all kinds of much less complex than living organisms!
So what? We are not really experienced in judging how chemical processes work across (a half of) billion year timespan. Or how can intense lighting and volcanic activity across similar timespans affect the probabilities of outcomes. And so on
Why is this process not ongoing now, then, when there are tons of prefab elements of life, i.e., it should be easier today than it was a billion years ago? A billion years is not as long as you think!
Doesn't multi-world interpretation pretty much answer how life originated?
I mean, even if the starting state require to bootstrap life have impossibly low chance to happen random, multi-world interpretation implies that there will be some worlds where it happened, and observation of life is only possible in such worlds..
Multi-worlds is not really relevant here. You are just asking the question how the building blocks of life form in the Universe and how can they reach a planet like ours.
That's not true. If life has the odds of one in a quadrillion of happening, and we're here to discuss it, then we're that one in a quadrillion. If we weren't, we wouldn't be alive. By definition, we were the lucky ones with the perfect conditions that resulted in us.
But I don't think we are "lucky", because we are part of the world, not something that was placed inside it by choice. It is like asking why is Nile in Egypt and not in some other place. If Nile is in some other place, it would not be Nile...So does it make sense to say that Nile is lucky to be in Egypt? No, I think it does not make sense...
Sorry, but nothing you have said here is true or makes sense. Multi worlds are universes, not worlds within our universe. The multiworld interpretation is one of several interpretations of quantum mechanics of the exact same evidence--one or the other interpretation being "true" has no empirical implications. And it is an interpretation of quantum mechanics, which has nothing to do with the distribution of nucleotides. And it's incoherent to call an observed event "impossible". You seem to mean that you think that it is highly unlikely, but offer no reason to think so ... nor for the bizarre claim that "Multi worlds is the only way". I suspect that you are mixing up a very confused understanding of "Multi worlds" with some version of the anthropic principle. But the anthropic principle is an a posteriori explanation of an a priori unlikely occurrence, it's not a "way" for something to happen.
I won't comment further unless you offer a convincing proof of your assertion.
Ok, what is the mystery in the origin of life? As I understand, it is how all the required molecules came together in the right configuration spontaneously? Is that the question that we are trying to answer?
If this is the question, I think the Multi Worlds Interpretation provides the answer. Because it says that there is some worlds where any given random event will manifest.
So it follows that there is some worlds, where this random event that we call the "origin of life" manifested. And it is just that we are part of one such world.
>multiworld interpretation is one of several interpretations of quantum mechanics of the exact same evidence
I think we might think the other way around. That the origin of life, as well as the fact that we seem to be alone in the universe, as a proof of the MWI..
About the latter, I think we have an overwhelming chance to be alone, because while it is true that there can be universes where random events have lead to origin of life in multiple places, the universes where there is only a single "origin of life" event will vastly outnumber such universes that the chances of us finding oursleves in one such universe (where life has originated independently more than once) is vanishingly small.
Fascinating that all five nucleobases were found in Ryugu samples. The fact that these formed abiotically in an asteroid environment strengthens the case that the building blocks of life are common throughout the solar system. The amino acid findings from the same samples were already compelling, but having the complete nucleobase set is a different level of evidence.
Ryugu showed an estimated ~20,000 different organic molecules. It's not that surprising that the nucleobases would be among them, along with all sorts of chemicals not relevant to life.
In the reference from the link for this HN entry, we see the nucleobases were present at concentrations of about 1 nano-mole per gram (< 1 ppm). They are minor constituents present in a sea of mostly non-biologically relevant compounds.
The missing part is how do they form self-replicating mechanisms capable of evolution. I doubt an asteroid with a bit of organic dust is enough for that. If such small amounts suffice we should see the formation of new life forms from scratch, today, left and right I think?
The timing of the delivery is what's important here. These building blocks, organic matter, and water would have been depleted in the proto-Earth due to Solar irradiation. There needs to be some mechanism that delivers these ingredients from the outer Solar System. Bombardment by smaller rocks makes the most sense, and was likely triggered by the migration of Giant Planets, leading to a period of heavy bombardment (on a bare Earth -- no oceans, no volcanoes).. https://en.wikipedia.org/wiki/Nice_model
Huh? Those smaller rocks would be even more irradiated, as they have no atmosphere?
They’d also have to contend with re-entry.
It would’ve been specifically asteroids from beyond the "frost line", where it’s cold enough for volatile substances to coalesce and stay solid.
"volatile substances" is doing a lot of work. This means water and organics. Literal cold-storage seeds of life.
[dead]
The smaller rocks are composed of those materials in solid state (e.g., ice not water). They are less irradiated as they are further away from the Sun (think the asteroid belt and beyond). Atmospheric entry (if that's what you mean) is irrelevant. What matters here is the transport of materials from a place where they could have formed, to a place where they couldn't.
Atmospheric entry is completely relevant because some people have made the illogical claim that meteorites falling on Earth could have contributed with such complex organic substances, like the nucleobases, to the appearance of life on Earth.
The icy bodies from the outer Solar System that contain such organic substances are very easily vaporized during entry in the atmosphere of the Earth, so only a negligible fraction, if any, of the organic substances originally present in such a body would reach the surface of the Earth.
Wouldn't a big enough asteroid have an inner part which survives entry? You seem to be saying that it's impossible for any meteorite that might have these chemicals to not be completely vaporized which seems doubtful. Have you got a source?
So you survived re-entry. Now, you get to survive impact. Seems like the energy released would also be damaging
Most asteroids have slowed to terminal velocity by the time they impact. It’s not nothing, but it’s mostly going to be relevant to physical processes and not chemical ones.
You might consider that scientists advanced enough in their field to be launching missions to retrieve dust from asteroids are actually aware of basic facts relevant to their field of study.
You might consider that even concepts like plate tectonics (which frankly are incredibly obvious if one just looks at a map) were considered ridiculous ideas by the most advanced experts in their field at one point. A point not that long ago.
I’m not saying the person you are responding too is right - but appealing to authority on something like this has a pretty bad track record.
[dead]
Quality of comments massively dropped on the HN. It feels like Facebook now.
The Redditors have arrived
Generally speaking small molecules aren't damaged by concussive shock.
I was thinking more of heat
So we get organic vapors in the atmosphere right. Shouldn't that matter?
One theory is that the primitive Earth contained much smaller quantities of the volatile chemical H, C, N, O and S, which are the main constituents of water and of organic substances.
Then Earth collided with a great number of small bodies formed in the outer Solar System, which were rich in water and organic substances. This has modified the composition of the Earth towards the current composition. (Later Earth has lost a part of its hydrogen; because hydrogen is very light, it is lost continuously from the upper atmosphere, after water is dissociated by ultraviolet light; thus now the Earth has less water than around the appearance of life.)
This theory is likely to be true, so meteorites probably have brought a good part of the chemical elements most needed by living beings.
However, most of the pre-existing organic substances from meteorites must have decomposed and whatever has been preserved of them could not have had any significant role in the appearance of life here, because any living being would have needed a continuous supply with any molecules that it needed, otherwise it would have died immediately. Such a continuous supply could have been ensured only for molecules that were synthesized continuously in the local environment here, not for molecules arriving sporadically in meteorites and which would have been diluted afterwards over enormous areas, down to negligible concentrations.
> Atmospheric entry (if that's what you mean) is irrelevant.
I think the OP meant that Earths magnetic field and atmosphere shields any terrestrial matter far more than than a bare asteroid that has no such protections, so it seems implausible at first glance that these things would develop or survive in open space rather than here.
> it seems implausible at first glance that these things would develop or survive in open space rather than here.
I don't think "organics developed in the vacuum of space" is implied. Survived? Well we have samples now confirming, if I'm understanding the basis for the discussion (the article).
We have some organic ‘building block’ compounds confirmed frozen on some asteroids.
But what we don’t have is any examples of them surviving re-entry.
We also have a massive amount of those same compounds already here on the planet.
Causality is… tenuous. But not impossible.
Causality was not the point. The point was to refute the seeding hypothesis, and because they found those molecules, the effort to falsify the hypothesis failed. Now we can move on to the next attempt to refute, which, as you say, might be to study whether molecules can survive conditions of reentry.
Experiments do not tell us that something IS a certain way; only the ways it is not.
The ideal situation for an expert is to prove causality!
It’s nearly impossible, but it is the holy grail!
This experiment was to try to falsify one theory, yes, but as you note that is a very long way from the actual goal - or the level of certainty that the article is trying to imply.
These articles are written due to funding needs, which is why the articles are the way they are - and why the scientists themselves are likely cringing too when they read these articles. At least until the checks (hopefully) arrive.
I was under the impression that the ejection of these compounds demonstrates that organics (blocks) can escape a gravity well, which implies they can likely re-enter another.
The earths poles?
Those smaller rocks are in the outer solar system, where the solar irradiation is lower. But the way they are composed is lots of ices (volatile molecules in solid form) being built on the silicate/graphite refractory core. The ices remain preserved in the environment provided by the outer solar system.
Extra terrestrial propagation of life, if real would have evolved to have non-zero survival rates in interstellar radiation regimes and timescales.
The fragility of life-as-we-know-it that has undergone serial passage in an environment largely shielded from radiation, is not necessarily representative of putative life-forms carried by little rocks in space.
I am neither convinced for nor against the idea that life may have been carried over by interstellar rocks: on the one hand, its a major promiscuity between celestial bodies within star systems, galaxies, etc. on the other hand since we haven't discovered other life forms yet we have no idea on the missing probability densities of life in the bulk of the universe, so the Bayesian catapult can swing either way, we just lack the data for now.
Meteorites are generally cold when they reach the surface of the earth. The heat of reentry is very brief and generally just on the surface. That's my understanding.
The surfaces are typically melted - the ones that don’t just explode anyway.
Icy meteorites never survive re-entry that I’m aware of; and most carbon/chondrite ones don’t either, but they are the most common type that do. They tend to be ‘dry’, however.
Re-entry is a very ‘angry’ process.
[flagged]
One thing I do agree with you: answering that an invisible dude did everything we don't get is much simpler indeed. Calling that a truth though.
The invisible dude is only simpler if you don't have to explain how the invisible dude was created.
"The simple truth" being Genesis, for which there can be no evidence possible?
pray tell, where do we learn this simple truth?
>pray tell, where do we learn this simple truth?
Praying[0] is a good start! That, coupled with large amounts of suspension of disbelief[1] helps too.
I suggest drinking (or whatever your preferred brain-fogger might be) heavily. That helps you ignore the details -- because the "devil is in the details" and we mustn't have that, right?
[0] Also known as "begging an imaginary sky daddy for help"
[1] https://en.wikipedia.org/wiki/Suspension_of_disbelief
I realize you're just replying in kind to the GP, who wasn't very nice himself. I also think it's not necessary to feed such trolls in a way that insults all the religious folks who do enjoy this site and don't try to push our faith on others.
I thought he was being tactfully humorous, yous daves. And you counted that as an insult?! jesus.
It's okay. I appreciate the cover, but it's important to let this oppressed, hunted, hated and endangered group have their say.
There is, after all, a war on Christmas, Christians and Christianity.
Christian enclaves are being attacked and Christians are being murdered in the thousands every week, just for being Christian.
Hundreds of decent, god-fearing Christian women are being raped daily by strong, manly Muslim men. Their strong muscles rippling under their tight clothes, stirring up strong, lustful feelings among the faithful Christian men.
It's no wonder that folks are kind of touchy. If you risked being shot, blown up, cuckolded or otherwise made dead or humiliated every time you went to a church, made the sign of the cross or put a "Jesus is my Co-pilot" bumper sticker on your vehicle, you'd be concerned wouldn't you?
And that happens every day because people hate them for their knowledge of the truth. It's all there in the literal word of god that's in the Holy Bible. Anything else is heresy. And we know what to do with heretics, don't we?
I guess it depends on how you define life, and whether we'd even recognize it when we see it, assuming we're looking in the right places.
I'd also imagine that any type of chemistry that harvests energy from the environment is liable to find itself as a food source at the bottom of the food chain now that earth is teeming with life.
I think that self-replication, and ability to harvest chemicals and energy from the environment to make more of what you're built of, is the point of complexification of chemistry that is best considered as the most primitive form of life. From there you can go on to things that are capable of encoding structure and more complex chemical factories.
I suppose one signature of these earliest type of "emergent life" chemistries would be localized concentrations of things like these nucleobases that we know are the building blocks of life as we know it, but there may be other types of self-replicating chemistries that emerge too, that don't lead anywhere.
> I think that self-replication, and ability to harvest chemicals and energy from the environment to make more of what you're built of, is the point of complexification of chemistry that is best considered as the most primitive form of life
Once there are forms that harvest and self-replicate, however, its expectable that there will be forms that delegate those features to others, like viruses. Cellular machinery that is required to implement those feature is not free, so parasitic forms would have survival advantage.
If we find some parasite the host can't be too far off.
read up on the RNA world theory, it's so cool
Have you seen this MLST interview of Blaise Aguera ?
https://www.youtube.com/watch?v=rMSEqJ_4EBk
He's an interesting person overall - the long interview is well worth watching if you haven't already seen it - but the relevance here are his experiments with the emergence of self-replicating computer programs out of random components.
His starting point is entire "programs" (random sequences of 64 characters, of which only ~7 have any meaning - the program "statements" of the BF language), so perhaps more suggestive of this RNA world stage, but perhaps also of what came before it when there may have been collectively self-replicating soups consisting of discrete components rather then entire structural encodings.
Parts of the RNA world theory are correct, but other parts are completely bogus and completely illogical.
What is correct is that RNA must have existed a very long time before DNA, during which RNA was the only nucleic acid.
Moreover, self-replicating RNA must have existed before ribosomes and proteins (where "protein" means a polypeptide that is synthesized using a RNA template).
It should be obvious that neither ribosomes nor protein-encoding RNA-sequences may exist before the existence of self-replicating RNA, because the living being in which those would exist would immediately die without descendants, together with its content of ribosomes and proteins.
So far so good, but some of the supporters of the RNA World theory claim that before the existence of protein-based enzymes, all chemical reactions inside a living being must have been catalyzed by RNA molecules.
This is an illogical claim, which is false beyond any reasonable doubt. Some RNA-based catalysts may have existed quite early, and some still exist today. However, any RNA-based catalyst could have appeared only at a later time after the establishment of RNA self-replication. The argument is the same as for protein-based catalysts, any living being with a RNA catalyst, but without RNA replication would die and the RNA catalyst would disappear without descendants.
So there is no doubt that the first feature of RNA that has appeared was self-replication, and at that time RNA could not have any other role inside a living being, because any such role would not have been inherited.
In other words, the first self-replicating RNA molecules were a kind of RNA virus, which multiplied inside the existing living beings, consuming energy and substances, without providing benefits. Only later, when eventually RNA templates have become the main method for synthesizing the useful components of a living being, something akin to a symbiosis between RNA and the rest of the living being was achieved, arriving to the structure of life that is known today.
For the first self-replicating RNA molecule to appear, the living beings must have contained abundant ATP and the other nucleotides. So the original role of the nucleobases in living beings was not the storage of information, but the storage of the energy required for synthesizing organic polymers. The self-polimerization of the nucleotides, which forms RNA, was an unwanted side reaction. In other words, before the RNA world, there already was an ATP world, which was the first user of nucleobases.
If RNA could not have been the material for making enzymes before the proteins, such enzymes must have been made from peptides (i.e. polymers of amino-acids), exactly like the enzymes of today, but those peptides must have not been synthesized using ribosomes, like the proteins. Such peptides still exist today and they remain widespread in all living beings, and they are named non-ribosomal peptides. Their mechanisms of synthesis are much less understood than the mechanisms of RNA-based protein synthesis. It is likely that more research into non-ribosomal peptides might provide a better understanding of how a living being without RNA could function.
In order to have a self-replicating living being you do not need a self-replicating molecule able to store arbitrary information, like RNA. It is enough to have a chain of synthesis reactions that closes a positive-feedback cycle, i.e. the products of one reaction are reactants for the next reaction and the products of the last reaction are the reactants for the first. If the chain of reactions produces all the components of a living being, growth and self-replication can be achieved.
The defect of such a living being is that evolution is extremely difficult. any mutation in one of the catalysts used in the chain of reactions is more likely to break the positive feedback and lead to death, instead of producing an improved living being. After the appearance of memory molecules, i.e. RNA and later DNA, which can store the recipe for making an arbitrary polymer molecule, it became possible to explore by mutations a much greater space of solutions, leading to a greatly accelerated evolution of the living beings.
I read a few times your comment and I went from "Nah" to "It makes a lot of sense". I'm adding the "ATP word" to my list of interesting ideas.
Some related stuff:
* https://www.science.org/doi/10.1126/science.adt2760 They made RNA that copies itself, but it use as a starting point activated triplets of bases. i.e, if ATP is AR-PPP, they use a mix of something compounds like AR-P-AR-P-AR-PPP that stil have the triphosphate to store energy and be easy to link, but already have tree linked bases. This is even more difficult that a soup of ATP and friends.
* https://en.wikipedia.org/wiki/PAH_world_hypothesis The idea is that before the RNA word, there was something simpler, like this. Is it possible to use ATP to build more PAH? I also remember about a version of RNA that instead of ribose it used something smaller (glicerol?), but I can't find it.
>However, any RNA-based catalyst could have appeared only at a later time after the establishment of RNA self-replication.
RNA by virtue of its biochemistry is capable of self replication already. Sequence affinity alone is sufficient to drive structure formation. But without a template, structure can also form on its own (example of an open access paper exploring one such mechanism under certain conditions, 1).
This would be enough to kick start things.
1. https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002...
Nope.
RNA is not capable of self replication. RNA by virtue of its biochemistry is only capable to be used as a template for replication, but the copying of the template must be done by a different molecular machinery.
If you put almost any RNA molecule in a jar together with monomers, you can wait until the end of time to see its replication.
Normally, RNA can be replicated only by a special enzyme, a RNA-dependent RNA polymerase. This kind of protein is used by many viruses.
It is hypothesized that a RNA molecule with a very special structure might have been used in the beginning as the catalyst for template-controlled polymerization, instead of a RNA-dependent RNA polymerase, to ensure self-replication. Some experiments have suggested that this is indeed possible.
Only after a self-replicating RNA molecule already existed, or if a RNA molecule existed in combination with a RNA polymerase that was produced by other means than by using a RNA template, other RNA molecules with various other functions could appear, and they would have been replicated by the already existing mechanisms, so they would be inherited by the descendants of a living being.
The link provided by you has nothing to do with RNA replication.
It describes a mechanism for the polymerization of nucleotides, which produces random nucleic acid molecules, not molecules that replicate an existing template.
A chemical reaction of this kind is what must have existed before the appearance of a self-replicating RNA molecule. Among the many random polymers produced before that, there was eventually one capable of self-replication, which started the evolution of genetic information.
This kind of reaction is what I have referred to as "side reactions" that happened during the use of ATP and of the other nucleotides as energy sources for the polycondensation reactions used in living beings to make macromolecules.
> RNA is not capable of self replication. RNA by virtue of its biochemistry is only capable to be used as a template for replication
RNA molecules which can synthesize others have been produced in a lab.[1,2] Your claim is not only totally unsupported, it's been experimentally disproven.
Laboratory RNA production can be done with regular batch chemistry - no enzymes involved, so on a long enough time span heat and mixing would be able to polymerase candidates out of the primordial soup.
RNA self-affinity is well documented, double-stranded RNA viruses exist[2] so stable conformational arrangements of RNA are not only experimentally proven but so viable they exist in todays much more enzymatically hostile world.
The relative difficulty of the structure persisting is a point in favor it is as a replication medium, since if RNA could tightly bind RNA then templating new strands would inactivate it.
[1] https://www.science.org/doi/10.1126/science.1060786
[2] https://www.pnas.org/doi/full/10.1073/pnas.1610103113
[3] https://en.wikipedia.org/wiki/Double-stranded_RNA
You sound awfully confident about this, given we have no direct evidence for most of your claims. I would find your writing more convincing if you didn't make absolute statements.
This theory is called panspermia [1] and it has several alternatives. One of the most extreme is that in the very early Universe, these building blocks could spread easily because the ambient temperature of the Universe was significantly higher than it is now. This isn't the most popular version.
The most popular is that asteroids and other interstellar bodies spread the building blocks, be it anywhere from amino acids to more complex building blocks. As evidence of this, there are hundreds of surviving asteroids on Earth that have been positively identified as having coming from Mars, which is pretty crazy because that basically takes a violent impact throwing debris into space and it making it to us many times over.
Part of the evidence for all this is how soon after the Earth formed that life appeared. We have positive evidence that this only took a few hundred million years. That's kinda crazy if you think about it. Also consider that the oceans likely came after the EArth formed.
Our galaxy is over 10 billion years old. The Sun is less than 5 billion years old. So that's 5+ billion years for stars and Solar Systems to form, evolve and die before the first fusion reaction in the Sun. Some of this needed to happen just to form heavy elements that are relatively abundant. Even that's kind of crazy. Heavy elements like lead, uranium and gold take relatively rare and violent events to eject material into space and make it to us. So what else made it to us?
[1]: https://en.wikipedia.org/wiki/Panspermia
Paints the picture of an early solar system that was a fairly connected system. Perhaps life didn’t form anywhere but Porto-life formed everywhere and earth is the only place that hasn’t died yet
The major flaw in Panspermia is that it all had to start somewhere without Panspermia. If it did that there, why not here?
We know 2 things that are apparently incoherent:
1 - Abiogenesis is incredibly rare. We don't know how much exactly, but it's a lot.
2 - Abiogenesis happened on Earth about as soon as it became possible. Where "as soon as" means within half a billion years, but it's still way quicker than its rarity implies.
A lot of people think panspermia is what made those two happen. Life had about a full billion years to appear in meteors before they could appear here.
There are some problems, e.g. that each meteor only stayed chemically active for less than that half-a-billion years Earth had. Or that all the meteors that fell on Earth had only a fraction of the material that was later available here. But IMO, the largest issue is that just doubling the time is absolutely unsatisfying.
Life cannot appear in any of the small bodies that become meteors, because there is no source of energy for it.
Life can appear only on big planets or on big satellites, like the big satellites of Jupiter and Saturn, if they have a hot interior and volcanism.
Volcanism brings at the surface substances that are in chemical equilibrium at the high temperatures of the interior, but which are no longer at chemical equilibrium at the low temperatures of the surface, providing chemical energy that can be used to synthesize macromolecules.
Solar energy cannot be used for the appearance of life. Capturing light requires very complex structures that can be developed only after a very long evolution and which cannot form spontaneously in the absence of already existing living beings.
The only theory of panspermia that is somewhat plausible is that life could have appeared on Mars, which had habitable conditions earlier than Earth. Then, some impacts on Mars have ejected fragments that have fallen as meteorites on Earth and some remote ancestors of bacteria have survived this interplanetary trip.
There are many meteorites on Earth that have their origin in impacts from Mars, so at least this part is known as being possible.
>Solar energy cannot be used for the appearance of life. Capturing light requires very complex structures that can be developed only after a very long evolution and which cannot form spontaneously in the absence of already existing living beings.
I think that is putting the cart well before the horse. Earliest "life" I would say looks something like a short sequence of random RNA, in some structure (as in secondary), in some solution, among some nucleotides, where brownian motion lead to collision with nucleotides in the chain that grow the chain and/or template off the chain and make a copy. The energy requirements for this sort of pre cell life are far less than cell based life which has to spend energy on cell membrane or wall building. Energy could be quite low, it would just reduce the number of interactions over time. Likely also that this pre cell "life" would not die either so long as it is protected somewhat by cosmic radiation bombarding the chain (although to an extent this is also a ripe source of mutagenic potential).
Not true.
What you describe is a perpetuum mobile.
No kind of life can exist without a continuous flux of energy. The formation of any organic polymers requires energy, it cannot happen spontaneously.
Nucleotides that collide do not form polymers in water. The polymerization of nucleotides and of amino-acids and of most other organic macromolecules is done by water extraction (a.k.a. polycondensation).
Water extraction inside water requires considerable energy (i.e. you must dry some thing while it is still submerged in water). This is provided by certain dehydrated molecules, like ATP, from which water must have been extracted as a result of capturing some energy from the environment.
The common ancestor of all living beings known on Earth obtained energy by the reaction between free hydrogen (dihydrogen) and either carbon monoxide or carbon dioxide. It is likely that the capability to use carbon dioxide has appeared later and the very first living beings were powered by the conversion of dihydrogen and carbon monoxide into acetic acid. The energy from this reaction was captured because the first result of the reaction was not free acetic acid, but acetic acid condensed with another molecule, like in the acetyl-CoA that is used today by all living beings. Than that condensed molecule could be used to extract water from other molecules, producing dehydrated molecules like ATP, which can be used for the polymerization of nucleic acids.
There is no way to circumvent the need for a continuous source of energy for the appearance of life. Besides the H2 and CO gases, there was an alternative source of energy that was used very early, but it is not known if it was already needed for the initial appearance of life or it began to be harvested at a later stage. This second source of energy is the difference in ionic concentration between the acidic water of the primitive ocean and the alkaline water that is produced by dissolving volcanic rocks in places like hydrothermal vents, where H2 and other gases are also produced. The ionic concentration gradients produce ionic currents, which can power certain chemical reactions, like they also do in all present living beings.
> no source of energy
Asteroids early in the solar system would be very radioactive due to short lived isotopes formed during the formation of the solar system. The existence of these isotopes is known from the patterns of decay products found in asteroids. The current guess is the early protoplanetary disk was bombarded by intense GeV-scale protons accelerated in the shock of a nearby supernova, causing large scale transmutation in the disk.
There is no known way in which nuclear radiation could have been the source of energy for the first living beings.
While a little radiation might have been beneficial at a later stage in the evolution of living beings, by increasing the frequency of random mutations, for a faster evolution, for the early living beings the only effect of radiation would have been to destroy them and prevent them for having descendants.
The only positive effect of the increased radioactivity in the early Solar System is that it is possible that not only the planets but also some smaller asteroids might have had warm interiors and volcanism.
So in none of the huge number of small bodies that exist in the Solar System there have ever been conditions for the appearance of life, but perhaps on some of the bigger asteroids there might have been such conditions, if they also had water and volatile chemical elements, besides a warm interior.
If life has ever appeared in such a place it must have used the same sources of energy that are known to have been used by the ancestors of life on Earth, i.e. gases and ionic gradients produced by chemical reactions between water and volcanic rocks.
> There is no known way in which nuclear radiation could have been the source of energy for the first living beings.
Nuclear energy is a source of energy for some current living beings, though. Underground ecosystems live on hydrogen produced by radiolysis.
> because there is no source of energy for it.
Couldn't it have started in the accretion disk?
There not only there was no known source of energy for the synthesis of organic polymers, but also everything, with the exception of interstellar dust particles, was in a gaseous state, not suitable for forming the structure of a living being.
It appears all the "disk" labels are categorical. The concept I'm trying to find the name for is the continuous, slow, asymptotic reduction in the number of disjoint particles/collections spinning around a star. All the relevant "disk" labels would probably be all those on the right side of this curve, where water is present.
I would think the Sun, with its photons and charged particles, and the various electrostatics (like triboelectric) involved, would be the energy source. The disk starts, somewhat evenly distributed, with a whole annulus of surfaces in the Goldilockz zone, with water, etc present. Through time, these bounce off one another, eject bits, stick on others, preserve bits in ice, etc, smearing/spreading whatever allowed their synthesis.
Looks like this maybe has merit, with organic molecules found [1].
(I'm far outside by expertise here.)
[1] https://www.eurekalert.org/news-releases/1091674
People make the inference that "early occurence of life" implies "life must be easy to start". But that inference requires the assumption that the chance of OoL (origin of life) remains mostly constant with time. An alternative would be that the conditions under which life could arise are transient, so life either starts early or not at all. We don't know enough about OoL to rule this out. Some chemicals that might be needed for OoL, like ammonia, are not stable for long. And if life originated in small asteroids, this might have only a few million years for it to occur while they are still warm enough from early short lived radioisotopes like Al-26.
It is indeed possible that in the early Solar System, before the short-lived radioactive elements completely decayed, there were some asteroids with good conditions for the appearance of life.
However, I would not describe those as small. The majority of the interplanetary bodies that orbit the Sun and which fall from time to time on Earth as meteorites are far too small to have ever had conditions for the appearance of life.
Even an asteroid like that which has wiped out the dinosaurs, with a diameter of a few km could not ever have suitable conditions.
Only relatively large asteroids, presumably with diameters from tens of km to hundreds of km, might have had warm interiors and volcanism for enough time to allow the appearance of life.
Such asteroids must also have been among those distant from the Sun, in order to contain enough water and volatile chemical elements.
The fact that the most volatile chemical elements are those most important for life is not due to chance, but due to the necessity. The volatile elements are those prone to forming covalent chemical bonds. Unlike the metallic or the ionic chemical bonds, the covalent bonds are strictly required for forming the complex molecular structures that may lead to living beings.
> However, I would not describe those as small. The majority of the interplanetary bodies that orbit the Sun and which fall from time to time on Earth as meteorites are far too small to have ever had conditions for the appearance of life.
So what? The meteorites that fall to Earth were not that size for their entire existence. They are fragments of larger bodies that have collided over the billions of years. Iron meteorites, for example, are remnants of the cores of larger bodies that were big enough to undergo melting and differentiation in the early solar system.
Moreover, "not all places are suitable for OoL, therefore no places are suitable for OoL" would be a non sequitur, so I don't see how what you're trying to say there leads anywhere useful.
One way to think about that is time required:
If earth is about 4 billion years old, but it takes say 400 trillion years for natural processes to produce this chemistry, then it happened out there not here.
This was a key reason why Hoyle preferred a steady state model of the universe — the part of the universe we inhabit needs to be very, very old for this stuff to work out, according to his thinking. A minority opinion, for sure, his rejection of the Big Bang model and timelines lost him a lot of respect among his peers. And his ideas could be wrong, I’m just pointing out that historically panspermia proponents have taken this position as to “why not here”.
One theory is that the early plasma shortly after big bang had the right conditions to set the life building block chemistry.
Imagine the entire universe contains those buildings block.
It had to start somewhere which is favourable to preserve the necessary molecules. Early Earth was not such place.
Admittedly, am layman, have only heard numerous sciencey folks talk about it, but we've found all these basic components in space already, naturally occurring, and while we've never to my knowledge recreated actual, genuine abiogenesis, we have observed every process required for abiogenesis to be a reasonable explanation for the origin of life.
As to your question on we should see the formation of new life everywhere, well, if we looked hard enough we might? The answer is competitive exclusion. Abiogenesis would've occurred on a remarkably clean earth: any life now emerging from the proverbial space dust is both almost certainly not preconfigured for this biosphere, and is instantly drowning in competing microorganisms that are. Anything that does form is likely quickly killed either by natural forces or competing organisms. Meanwhile, our life goes everywhere: We've found living bacteria on the outside of the ISS!
> Wouldn't a couple asteroids be the literal drop in the ocean in comparison?
Actually most water on earth probably came from asteroids, so they are the entire ocean! They would also have brought a lot of frozen methane and ammonia, so most of the chemicals necessary for terrestial life.
When the solar system was forming, the protoplanetary ring of cosmic dust would have consisted of heavy elements (some essential for life, such as phosphorus) closer to the sun and frozen lighter elements further away. The heavy elements would have combined into the early rocky earth, and as the other planets formed and orbits stabilized the icy asteroids from further out would have been flung around and impacted the planets.
https://en.wikipedia.org/wiki/Late_Heavy_Bombardment - possibly?
There is some skepticism now that the LHB was real.
https://www.youtube.com/watch?v=IZfzbEtKF9o
My layman guess would be that shortly after formation Earth was just a ball of lava that destroyed every organic component so when the surface solidified it was sterile.
It was probably a ball of lava again when the moon formed after the impact too
Yep, you are 100% correct. In fact, it is much more likely they were originating on Earth itself than a random hobo asteroid.
> The missing part is how do they form self-replicating mechanisms capable of evolution.
Well, there are some missing parts, yes, but RNA can self-replicate already; at the least some RNA can. Ribosomes also contain RNA so its is a ribozyme.
RNA can replicate in highly artificial conditions that would seem to already require life to occur.
https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002...
That's not replication, that's polymerization. There's nothing template-directed about it, and as far as I can tell the experiment depends on pure initial conditions (the guanosine monophosphate is not mixed with a plethora of other chemicals that could copolymerize with it.)
That purity is the kind of artificiality I was talking about. A bad habit of OoL research is to show that some chemical shows up in trace amounts, then starting the next stage of experiments with a pure batch of that chemical. Robert Shapiro in his 1986 book "Origins" had some very biting things to say about this (the book is not nice to creationists either, btw.)
Once you have that initial polymerization, thats it, game over, now you can template right off that.
https://pmc.ncbi.nlm.nih.gov/articles/PMC7496532/
Again, implausible purity there. I'll add the tetramers used as the components are also much larger than the nucleotides in the Ryugu paper, so would be present in much lower concentrations.
I agree. If we knew the mechanism for how life started we'd probably be doing the experiments to prove it. There are theories and experiments that suggest some life-like processes can happen with inorganic compounds, but they require a lot of squinting and a bit of imagination to connect with our own origins. And there's a big difference between experiment and nature. On the one hand, we have people trying to make it happen, while on the other hand, it apparently already happened once, without anyone even needing to be around.
Which is underplaying what "trying" means in this context: we live on a planet with a lot of life - life which by definition was a superior competitor to the much simpler life it supplanted. The world, even enzymes from our skin, are unimaginably hostile to most candidates for simpler primordial lifeforms.
The reason showing abiogenesis is hard is because (1) everything in the biosphere would kill and eat the result and (2) the one thing it had going for it was time - millions of years of random diffusion with nothing else busy executing a grey goo type attack on all the available resources.
Frankly if someone gets abiogenesis to work in a lab environment within a single human lifetime, it wouldn't just be evidence for how it might've happened in Earth's past it would more or less set the parameters for how much life there must be in the universe everywhere because a mere 50 to 100 years to kickstart anything would be insane.
> One longstanding theory is that life first began on Earth when asteroids carrying fundamental elements crashed into our planet long ago.
That theory is bullocks. When an asteroid enters the atmosphere and crashes as high speed on the surface, you get a huge amount of energy that creates an explosion and a destruction of most complex chemical material in the process. It's no mistake that these kind of impacts are counted in the same range as multiple atomic or hydrogen bombs.
[dead]
Comets is where many astronomers have long thought the ocean came from. Comets are literal drops in our ocean. LOTS of comets. The atmosphere and the Earth at large would have been very different, and being bombarded by many giant space snowballs (along with asteroids) would have contributed materials. The missing part is, um, missing. We still do not know. However, these samples contained building blocks, not actual self-replicating RNA. That might seem like nothing, but before this discovery, we thought they only contained one ingredient.
One thing that is beginning to be appreciated is, if you have building blocks, under the right conditions, you also have self replicating RNA.
https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002...
That is not about the replication or self-replication of RNA.
The article is about a mechanism that may produce random nucleic acid molecules, i.e. molecules that do not replicate any template.
Reactions of this kind, producing random nucleic acids, must have existed long before the appearance of the first self-replicating RNA, thus before the appearance of any nucleic acid that could be inherited by the descendants of a living being and that could provide any useful feature for that living being.
Once you have one RNA it can serve as a template for others.
https://pmc.ncbi.nlm.nih.gov/articles/PMC7496532/
Meteorites
Well the competition might be too fierce for any new life to develop
We could artificially create a sterile, large pool of the ingredients and see what happens.
I've read about experiments like this but only at lab beaker scale.
I don't think you'd want a single homogeneous "large pool", but rather a large variety of different types of micro-environment, including all those that have been suggested as possible environments for the emergence of life - the chemical and physical environments of hydrothermal vents, volcanic hot springs, shorelines, different types of rocks, clays, etc. You'd want to have environments that included all energy sources present on earth (solar, lightening, geothermal), all forms of mechanical agitation/mixing (hydrothermal, waves), etc, etc.
The bigger the pool the harder to create it here on Earth without introducing problems. For example, take a prion. Hard as hell to actually get rid of, how do you know you've not actually introduced something like this to your sterile pool that's going to make it do things you don't expect.
Yeah, but it seems impossible to experiment on the scale that would have happened in nature where there would have been millions of localized "test tube experiments" ongoing for millions of years.
Of course people can, and do, try to replicate early earth environments and self-assembling proto-cells, but I'm not sure how intellectually satisfying any self-replication success from these "designer experiments" would be, unless perhaps done on such a large scale (simulation vs test tube?) that any conclusions could be made about what likely happened in nature - just how specific do the conditions need to be?
My personal theory is that the conditions for life are plentiful in the universe but it probably took an unbelieavable number of random chemical/mechanical events to form the first proto-lifeform.
Yet actual life remains to be discovered...> Yet actual life remains to be discovered...
We've barely started to look, other than on Mars, and notably we are seeing possible signs there. There may even still be primitive life there.
If we do find life of Mars, or say Europa, i.e. in the very first places we look for it, that that would be highly suggestive that it is extremely common (at least in primitive form).
Also it seems that finding a balance where an ecosystem doesn’t kill itself with its own waste is probably harder than we assume. Earth life has totally changed the atmosphere of the planet, I would many it many cases even when life does for it kills itself early on
It's funny talking about non software stuff on HN. I'm sure there's hundreds of papers on simulations and expert analysis of this.
Surely in a minority, but I do see posts from people on HN that are scientists, researchers, even mechanics and such. We definitely get a lot of speculation, but I've learned never to underestimate the level of expertise of people in our community.
Then please link the best ones? Or write some of your high-level thoughts about it.
You don't need to be an expert to be curious. Many here would surely like to know more. That's why non-IT stories are upvoted in the first place.
The biology equivalent of "infinite monkeys at a typewriter"
Does 'we' include 'you'?
The missing part has been conducted in other experiments. I don’t have time to give you some papers, but nucleic acids can self assemble into long chains under the right condutions. No polymerase enzyme is needed.
The conditions, while not requiring enzymes, are still highly artificial.
Why are you assuming couple of asteroids? Life first appeared 3.5 billion years ago. The frequency of an asteroid impact on Earth is ~500,000 years.
> The frequency of an asteroid impact on Earth is ~500,000 years.
Surely you could make this figure be anything you want just by scaling up or down the size of an object you call an asteroid. So as stated it's meaningless.
Fair. That number is for a rock of size 1 km.
https://catalina.lpl.arizona.edu/faq/how-often-do-asteroids-...
> I'm no expert but this sounds strange.
A cynic might suggest the theory might exist because nobody could figure out how life got started on its own on earth.
The thing is I've never found the asteroid theory particularly satisfying either because it simply inserts another abstraction layer, explaining the problem away rather than explaining it.
That's not to say it's wrong but, in its current incarnation, it's just a bit meh.
I suppose perhaps that's part and parcel of it being a very hard problem to solve.
[dead]
There are 2 distinct kinds of claims made about the role of meteorites fallen on Earth whose origin is in such bodies like the Ryugu asteroid.
One claim, which is likely to be true, is that in the beginning the Earth had a lower content of volatile elements, e.g. hydrogen, nitrogen, carbon, oxygen and sulfur, than today. The reason is that Earth has condensed at a high temperature, being close to the Sun, and those elements would not have condensed.
Later, the Earth has been bombarded by a great number of asteroids formed far from the Sun, which were much richer in H, C, N, O and S, and this bombardment has provided a major part of the chemical elements required for water and for organic substances.
A second, different claim, which is almost certainly false, is that this bombardment of the Earth has provided not only the raw chemical elements, but also pre-synthesized organic substances, like amino-acids and nucleobases, which have taken part directly in the origin of life.
This second claim does not make sense. The meteorites rich in water and organic substances are extremely easily vaporized during atmospheric entry or during the impact with the surface and their content of organic substances would decompose.
Even if we suppose that some falling bodies were so big that parts of them survived until the surface, any organic substances thus brought on Earth could not help in any way the appearance of life.
Any form of life would need a continuous supply of such substances, otherwise immediately after consuming the few molecules adjacent to it the life form would die without descendants.
Life can appear only in a place where there is a continuous supply of energy and it can use only chemical substances that are continuously synthesized in abiotic conditions. It cannot appear based on sporadic events, like the fall of a meteorite, which would also destroy anything at its place of impact.
Such places where energy is available continuously and there are also the substances from which complex organic substances can be synthesized through catalysis by various minerals, mostly metallic sulfides, exist both on Earth and in other places in the Solar System. These are the places where either volcanic gases are released or similar gases are produced by the reaction of water with volcanic rocks, in hydrothermal vents. As far as we know, those are the places where life must have appeared, because all the necessary ingredients exist. The only mysterious part is how it has happened that a correct combination of the mineral catalysts required to synthesize all the needed organic molecules happened to be located in close proximity and in the right sequence.
Today, even if such places still exist on Earth, life could not appear again. First, the oxygen from air would destroy any substances thus formed, and even where oxygen is missing the ubiquitous bacteria would consume any organic substances that could form abiotically, preventing their accumulation and the formation of any kind of structure from them.
> This second claim does not make sense. The meteorites rich in water and organic substances are extremely easily vaporized during atmospheric entry or during the impact with the surface and their content of organic substances would decompose.
Such meteorites fall to Earth even today. Their interiors are often ice cold.
I'm in the middle of reading Peter Brannen's The Story of CO2 Is the Story of Everything—it's excellent and goes deep into the (bio)geochemistry of Earth—and he presents a good case for a metabolism-first development of life, taking advantage of "a disequilibrium that needed to be relieved at the vents, an unending stream d free energy to dissipate," rather than the RNA information-first theories.
It fits his overall narrative but it was an interesting way to think about life "as a thermodynamically necessary mechanism to relieve the continuous production of free geochemical energy on Earth... more efficiently than abiotic processes could." (Brannen quoting complex-systems scientist Anne-Marie Grisogono) I highly recommend the book.
This is similar to Nick Lane's books, and the research he references as well. The necessity for disequilibrium, the emphasis on life as the movement of energy across a barrier, etc.
I'm no expert but it seems most reasonable to me. The continual talk about pre-biotic soups of ingredients seems profoundly misplaced.
It contains nucleobases. But does it contain ribose, or ribose linked to the nucleobases, or to phosphates? And more generally, does it also contain a grab bag of related chemicals that are not building blocks? The existence of such blocks as minor constituents of a soup of random chemicals doesn't mean much, especially as the concentration of any such constituent declines exponentially with its complexity.
https://www.nasa.gov/missions/osiris-rex/sugars-gum-stardust...
> The five-carbon sugar ribose and, for the first time in an extraterrestrial sample, six-carbon glucose were found.
The soup does matter, as does finding that the ingredients are everywhere.
Finding exponentially decreasing amounts of specific chemicals is about as informative as finding short words in strings of random letters.
Finding short words in strings of random letters at least establishes the existence of letters and words.
It doesn't demonstrate the existence of Shakespeare's works, but it's a building block that's good to know exists.
All it means is you can say "if life is rare, it's not because these specific small chemicals can't be produced". Which is a rather weak thing to say. It doesn't imply life isn't rare, or that further advancement the existence of these small building blocks is easy or inevitable.
> All it means is you can say "if life is rare, it's not because these specific small chemicals can't be produced".
This is absolutely a good finding to have in your pocket.
"Good"? Ok, if it makes you feel better. But scientifically, it doesn't do much.
Whats your problem with this topic? Highly confronting posts about nothing. Iterative approach to science seems foreign here.
There's a tremendous amount of confidently stated bullshit on the issue of OoL that I have long since lost all patience with.
What's your problem with the debunking of falsehood?
You asked "does it contain ribose"; I answered (with a reputable source) in the affirmative.
Where's the falsehood?
I also asked about other things you have conveniently forgotten to mention there.
The overarching falsehood is that identification of biologically relevant molecules at 200 ppb levels, in a soup of tens of thousands of other chemicals, moves the needle any in figuring out OoL.
Finding strong things here is going to be difficult. Sometimes you have to take a bunch of weak things to figure out where they lie for guidance.
It's a sample of one, but I think the takeaway is just that if the nucleobases are present on a random asteroid then they probably commonly occur. Of course as you note it takes a lot more than that to form these into nucleic acids.
I would guess there is a more primitive stage in the emergence of life where self-replicating soups (Kaufmann: metabolisms), including things like nucleobases and amino acids, capable of collective replication/expansion exist, before we get anything as sophisticated as nucleic acids and structural encoding.
The nucleobases can self polymerize into nucleic acids
Since nucleobases contain neither sugars nor phosphates, no they can't.
Nucleotides*
They didn't discover nucleotides on this asteroid.
I wonder how they prevent contamination of the containers used to collect and store samples.
I assume they have to be ultra clean in every sense of the word 'clean' with the cavity pulled to a vacuum. And also the equipment that collects the sample and puts it into the canister has to be clean as well.
The logistics aren't obvious to me at all
They seem pretty confident. There's been some conflicting reporting on contamination of the Ryugu samples over time.
https://phys.org/news/2024-11-ryugu-asteroid-sample-rapidly-...
> Researchers from Imperial College London have discovered that a space-returned sample from asteroid Ryugu was rapidly colonized by terrestrial microorganisms, even under stringent contamination control measures.
https://www.isas.jaxa.jp/en/topics/003899.html
> As described in the discussion of the journal paper, all samples received from JAXA have undergone the initial description, storage, and sealing in dedicated containers under a nitrogen atmosphere. The samples are distributed to researchers without exposure to the Earth's atmosphere. The possibility of microbial contamination is therefore considered extremely low. In addition, organic and microbial contamination assessment of the environment at the curation facilities within JAXA (clean chamber) in which the Ryugu sample grains undergo the initial description are conducted 1 ~ 2 times a year. It has been confirmed and reported that the concentration of organic matter is at or below the same level as that of the OSIRIS-REx asteroid return sample glove box at the NASA Johnson Space Center, and that no microbial colonies have been detected in the microbial contamination assessment conducted with swabbing and culture medium (Yada et al., 2023). Based on these facts, we agree that the microbial contamination described in the paper did not occur during a process within JAXA, but under the laboratory environment of the allocated researchers.
ty ty! I usually just give a quick chatgpt buy my work blocked every ai but copilot
Please don't just post slop anyone else could have gotten from AI. It undermines the entire purpose of this site, and reduces the quality of discourse drastically.
GP probably meant he would've relied on chatgpt instead of the help of a kind user to get the same info, not that he would actually post it here.
[dead]
https://science.gsfc.nasa.gov/sed/content/uploadFiles/public...
you're the reason why I love HN.
Thank you. Very kind of you to take the time and trouble...
Ummm ... the "Victoria University of Wellington in Australia"? Please. Victoria University is located in Wellington, New Zealand [1]. Nothing to do with Australia. Dr. Morgan Cable is a Senior Lecturer in Space Science at Te Herenga Waka, Victoria University of Wellington in New Zealand [2]. Can't believe that phys.org would publish such an error.
[1] https://www.wgtn.ac.nz/
[2] https://www.psi.edu/staff/profile/morgan-cable/
First time I’ve seen my university mentioned online and it’s the wrong country!
That's not really new. It seems as if some people try to project "there is life outside of planet Earth". Well, the thing is ... is this question important? You already have life here. Synthetic biology will also progress. So why is it important if life is anywhere else? I don't understand it.
There is nothing magic in RNA or DNA. Granted, right now we can not easily explain how life gets "bootstrapped", but recently there was a paper of self-propagating RNA even of a kind of semi-random sequence; this RNA can just amplify itself. I am sure you can find many more similar examples eventually as well as biochemical reaction processes that can be "bootstrapped" - and I am also sure none of these work on an asteroid. So why is there this strange focus on "life outside of planet Earth"? Some people want research money, that is clear now.
Why study anything new? You survived this far without it, after all :)
> It seems as if some people try to project "there is life outside of planet Earth". Well, the thing is ... is this question important? You already have life here.
How common the building blocks of life are out in the universe has important implications for open questions like the intersection of the Drake Equation and the Fermi paradox which has likely relevance to our own future here on Earth.
...though I happen to think what we know so far isn't comforting in the sense that the building blocks of life do appear to be very common and the most likely reason that we have to ask "Where is everybody?" in spite of that is that the Great Filter is probably expansionist self-destruction of the sort we are currently speed-running as a society.
The most important question we all want answered is just how rare life is in the Universe. The fact that the building blocks are there just floating around on asteroids makes it that much more likely that its quite common.
If you look at the paper, the nucleobases were present at concentrations of about 1 nanomole per gram. So, maybe 200 ppb by mass for each. They are in a sea of other random organic stuff that is at best tangentially relevant to life as we know it.
I’ve wondered before if the idea that life originated on Earth might be the last geocentrism to fall.
Speculation of course, but it would fit a certain historical pattern.
Maybe life is all over the damn place, just a thing that happens under certain thermodynamic constraints, and it arrived on board comets or some similar mechanism.
Maybe space contains spores of minimal super simple organisms that can survive being vacuum freeze dried for incredibly long periods of time. When they land somewhere suitable they do stuff.
Maybe life originated long, long ago. The wildest speculation I have is that it originated shortly after the big bang during a brief period when the temperature of the universe was temperate, but that’s very far fetched for numerous reasons. More likely that it pops up from time to time and spreads over cosmic time scales.
But it only evolves to high levels of complexity in environments that are very friendly to a lot of life, have abundant energy, and are stable enough for a very long time. That may be the rare thing.
Are these building blocks not evaporated on impact?
Only the outer surface of asteroids gets hot. Atmospheric entry isn’t long enough to thoroughly cook a rock.
What about the immense energy that is released when it slams into the earth at supersonic speeds?
A asteroid has to be absolutely huge to make it all the way down to the surface without slowing down to terminal velocity. Your typical 1kg asteroid will have slowed to terminal velocity dozens of km above the surface. The smaller an object the lower the ratio of its mass to surface area and the more easily it slows down.
How are samples collected? In space or as debris?
From near the start of the article: "In 2014, the Japanese spacecraft Hayabusa-2 blasted off on a 300-million-kilometer (185-million-mile) mission to land on Ryugu, a 900-meter-wide (2,950-feet-wide) asteroid. It successfully managed to collect two samples of rocks weighing 5.4 grams (under a fifth of an ounce) each and bring them back to Earth in 2020."
Surface sample: Hayabusa2's sampling device is based on Hayabusa's. The first surface sample retrieval was conducted on 21 February 2019, which began with the spacecraft's descent, approaching the surface of the asteroid. When the sampler horn attached to Hayabusa2's underside touched the surface, a 5 g (0.18 oz) tantalum projectile (bullet) was fired at 300 m/s (980 ft/s) into the surface.[72] The resulting ejected materials were collected by a "catcher" at the top of the horn, which the ejecta reached under their own momentum under microgravity conditions.
Sub-Surface Sample: The sub-surface sample collection required an impactor to create a crater in order to retrieve material under the surface, not subjected to space weathering. This required removing a large volume of surface material with a powerful impactor. For this purpose, Hayabusa2 deployed on 5 April 2019 a free-flying gun with one "bullet", called the Small Carry-on Impactor (SCI); the system contained a 2.5 kg (5.5 lb) copper projectile, shot onto the surface with an explosive propellant charge. Following SCI deployment, Hayabusa2 also left behind a deployable camera (DCAM3)[Note 1] to observe and map the precise location of the SCI impact, while the orbiter maneuvered to the far side of the asteroid to avoid being hit by debris from the impact.
It was expected that the SCI deployment would induce seismic shaking of the asteroid, a process considered important in the resurfacing of small airless bodies. However, post-impact images from the spacecraft revealed that little shaking had occurred, indicating the asteroid was significantly less cohesive than was expected.[76]
Duration: 36 seconds.0:36 The touchdown on and sampling of Ryugu on 11 July Approximately 40 minutes after separation, when the spacecraft was at a safe distance, the impactor was fired into the asteroid surface by detonating a 4.5 kg (9.9 lb) shaped charge of plasticized HMX for acceleration.[56][77] The copper impactor was shot onto the surface from an altitude of about 500 m (1,600 ft) and it excavated a crater of about 10 m (33 ft) in diameter, exposing pristine material.[15][32] The next step was the deployment on 4 June 2019 of a reflective target marker in the area near the crater to assist with navigation and descent.[33] The touchdown and sampling took place on 11 July 2019.[34]
https://en.wikipedia.org/wiki/Hayabusa2#Sampling
Anyone else think a universal intelligence is behind seeding planets with these rocks?
Like a god? No.
Or like some ancient alien species that travelled the stars but found it was alone, like in the ST:TNG episode[0]? No too.
Even if these ancient aliens thought it would be fun to spread their sperm all over asteroids and fling them out into the universe, there wouldn't be enough time for those rocks to get anywhere.
The more logical conclusion is that abiogenesis happens everywhere in the universe under the right conditions.
[0]: https://en.wikipedia.org/wiki/The_Chase_(Star_Trek:_The_Next...
No one with any sense.
So what?! This does not prove anything! There are stones all around us, but they don't assemble themselves into beautiful, majestic stone buildings! All ingredients of concrete are around us, but we don't see them turning into concrete and pouring themselves into freeways, bridges, and all kinds of much less complex than living organisms!
I just walked into a room and everywhere I look, everything I see is made up of the same basic building blocks.
The only thing left to figure out is how did these legos learn to assemble themselves.
So what? We are not really experienced in judging how chemical processes work across (a half of) billion year timespan. Or how can intense lighting and volcanic activity across similar timespans affect the probabilities of outcomes. And so on
Why is this process not ongoing now, then, when there are tons of prefab elements of life, i.e., it should be easier today than it was a billion years ago? A billion years is not as long as you think!
Fred Hoyle suggested this back in the seventies and eighties and was berated for it.
Doesn't multi-world interpretation pretty much answer how life originated?
I mean, even if the starting state require to bootstrap life have impossibly low chance to happen random, multi-world interpretation implies that there will be some worlds where it happened, and observation of life is only possible in such worlds..
Multi-worlds is not really relevant here. You are just asking the question how the building blocks of life form in the Universe and how can they reach a planet like ours.
I mean, Multi worlds is the only way this impossibly random event can occur on its own.
That's not true. If life has the odds of one in a quadrillion of happening, and we're here to discuss it, then we're that one in a quadrillion. If we weren't, we wouldn't be alive. By definition, we were the lucky ones with the perfect conditions that resulted in us.
That is what I meant.
But I don't think we are "lucky", because we are part of the world, not something that was placed inside it by choice. It is like asking why is Nile in Egypt and not in some other place. If Nile is in some other place, it would not be Nile...So does it make sense to say that Nile is lucky to be in Egypt? No, I think it does not make sense...
Sorry, but nothing you have said here is true or makes sense. Multi worlds are universes, not worlds within our universe. The multiworld interpretation is one of several interpretations of quantum mechanics of the exact same evidence--one or the other interpretation being "true" has no empirical implications. And it is an interpretation of quantum mechanics, which has nothing to do with the distribution of nucleotides. And it's incoherent to call an observed event "impossible". You seem to mean that you think that it is highly unlikely, but offer no reason to think so ... nor for the bizarre claim that "Multi worlds is the only way". I suspect that you are mixing up a very confused understanding of "Multi worlds" with some version of the anthropic principle. But the anthropic principle is an a posteriori explanation of an a priori unlikely occurrence, it's not a "way" for something to happen.
I won't comment further unless you offer a convincing proof of your assertion.
Ok, what is the mystery in the origin of life? As I understand, it is how all the required molecules came together in the right configuration spontaneously? Is that the question that we are trying to answer?
If this is the question, I think the Multi Worlds Interpretation provides the answer. Because it says that there is some worlds where any given random event will manifest.
So it follows that there is some worlds, where this random event that we call the "origin of life" manifested. And it is just that we are part of one such world.
>multiworld interpretation is one of several interpretations of quantum mechanics of the exact same evidence
I think we might think the other way around. That the origin of life, as well as the fact that we seem to be alone in the universe, as a proof of the MWI..
About the latter, I think we have an overwhelming chance to be alone, because while it is true that there can be universes where random events have lead to origin of life in multiple places, the universes where there is only a single "origin of life" event will vastly outnumber such universes that the chances of us finding oursleves in one such universe (where life has originated independently more than once) is vanishingly small.
Fascinating that all five nucleobases were found in Ryugu samples. The fact that these formed abiotically in an asteroid environment strengthens the case that the building blocks of life are common throughout the solar system. The amino acid findings from the same samples were already compelling, but having the complete nucleobase set is a different level of evidence.
Ryugu showed an estimated ~20,000 different organic molecules. It's not that surprising that the nucleobases would be among them, along with all sorts of chemicals not relevant to life.
https://www.science.org/doi/10.1126/science.abn9033
In the reference from the link for this HN entry, we see the nucleobases were present at concentrations of about 1 nano-mole per gram (< 1 ppm). They are minor constituents present in a sea of mostly non-biologically relevant compounds.
[dead]