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?
BinaryAsteroid 8 hours ago [-]
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
lazide 8 hours ago [-]
Huh? Those smaller rocks would be even more irradiated, as they have no atmosphere?
They’d also have to contend with re-entry.
Sharlin 7 hours ago [-]
It would’ve been specifically asteroids from beyond the "frost line", where it’s cold enough for volatile substances to coalesce and stay solid.
jvanderbot 5 hours ago [-]
"volatile substances" is doing a lot of work. This means water and organics. Literal cold-storage seeds of life.
BinaryAsteroid 8 hours ago [-]
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.
adrian_b 6 hours ago [-]
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.
foxglacier 42 minutes ago [-]
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?
soco 4 hours ago [-]
So we get organic vapors in the atmosphere right. Shouldn't that matter?
adrian_b 3 hours ago [-]
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.
lazide 5 hours ago [-]
The earths poles?
naasking 7 hours ago [-]
> 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.
kmaitreys 7 hours ago [-]
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.
general_reveal 3 hours ago [-]
Exactly. The attempt to try to explain creation through science is often more absurd than the simple truth.
xandrius 2 hours ago [-]
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.
blacksmith_tb 2 hours ago [-]
"The simple truth" being Genesis, for which there can be no evidence possible?
vpribish 2 hours ago [-]
pray tell, where do we learn this simple truth?
GetTheFacts 29 minutes ago [-]
>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"
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.
majkinetor 3 hours ago [-]
> 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.
make3 8 hours ago [-]
read up on the RNA world theory, it's so cool
HarHarVeryFunny 7 hours ago [-]
Have you seen this MLST interview of Blaise Aguera ?
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.
adrian_b 4 hours ago [-]
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.
Vrondi 1 hours ago [-]
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.
dan_hawkins 6 hours ago [-]
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.
8bitsrule 7 hours ago [-]
The major flaw in Panspermia is that it all had to start somewhere without Panspermia. If it did that there, why not here?
marcosdumay 5 hours ago [-]
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.
adrian_b 4 hours ago [-]
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.
nomel 22 minutes ago [-]
> because there is no source of energy for it.
Couldn't it have started in the accretion disk?
kmaitreys 7 hours ago [-]
It had to start somewhere which is favourable to preserve the necessary molecules. Early Earth was not such place.
michaelsbradley 6 hours ago [-]
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”.
HarHarVeryFunny 6 hours ago [-]
> 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.
bartread 49 minutes ago [-]
> 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.
Well the competition might be too fierce for any new life to develop
0x000xca0xfe 9 hours ago [-]
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.
HarHarVeryFunny 8 hours ago [-]
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.
pixl97 9 hours ago [-]
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.
HarHarVeryFunny 8 hours ago [-]
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?
0x000xca0xfe 8 hours ago [-]
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.
Yet actual life remains to be discovered...
edgyquant 32 minutes ago [-]
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
HarHarVeryFunny 8 hours ago [-]
> 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).
sph 1 hours ago [-]
The biology equivalent of "infinite monkeys at a typewriter"
make3 8 hours ago [-]
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.
freedomben 6 hours ago [-]
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.
0x000xca0xfe 7 hours ago [-]
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.
moralestapia 8 hours ago [-]
Does 'we' include 'you'?
kmaitreys 7 hours ago [-]
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.
jmyeet 7 hours ago [-]
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
ToucanLoucan 8 hours ago [-]
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!
shevy-java 5 hours ago [-]
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.
pfdietz 4 hours ago [-]
RNA can replicate in highly artificial conditions that would seem to already require life to occur.
kjkjadksj 5 hours ago [-]
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.
pfdietz 4 hours ago [-]
The conditions, while not requiring enzymes, are still highly artificial.
adrian_b 5 hours ago [-]
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.
pfdietz 4 hours ago [-]
> 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.
Amorymeltzer 4 hours ago [-]
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.
pfdietz 10 hours ago [-]
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.
> 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.
pfdietz 9 hours ago [-]
Finding exponentially decreasing amounts of specific chemicals is about as informative as finding short words in strings of random letters.
ceejayoz 9 hours ago [-]
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.
pfdietz 9 hours ago [-]
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.
ceejayoz 9 hours ago [-]
> 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.
pfdietz 8 hours ago [-]
"Good"? Ok, if it makes you feel better. But scientifically, it doesn't do much.
pixl97 8 hours ago [-]
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.
HarHarVeryFunny 9 hours ago [-]
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.
kjkjadksj 5 hours ago [-]
The nucleobases can self polymerize into nucleic acids
fusslo 9 hours ago [-]
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
ceejayoz 9 hours ago [-]
They seem pretty confident. There's been some conflicting reporting on contamination of the Ryugu samples over time.
> 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.
fusslo 9 hours ago [-]
ty ty! I usually just give a quick chatgpt buy my work blocked every ai but copilot
Refreeze5224 4 hours ago [-]
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.
Thank you. Very kind of you to take the time and trouble...
stevenjgarner 5 hours ago [-]
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.
Are these building blocks not evaporated on impact?
stouset 8 hours ago [-]
Only the outer surface of asteroids gets hot. Atmospheric entry isn’t long enough to thoroughly cook a rock.
drob518 7 hours ago [-]
What about the immense energy that is released when it slams into the earth at supersonic speeds?
Symmetry 6 hours ago [-]
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.
8 hours ago [-]
hmokiguess 9 hours ago [-]
How are samples collected? In space or as debris?
mkl 47 minutes ago [-]
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."
sheikhnbake 9 hours ago [-]
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]
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.
qsera 8 hours ago [-]
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..
kmaitreys 6 hours ago [-]
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.
zenon_paradox 9 hours ago [-]
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johnsmalles 8 hours ago [-]
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.
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?
They’d also have to contend with re-entry.
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.
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.
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.
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'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.
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.
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.
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.
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 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.
Couldn't it have started in the accretion disk?
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”.
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.
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.
https://www.youtube.com/watch?v=IZfzbEtKF9o
I've read about experiments like this but only at lab beaker scale.
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?
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).
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 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
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!
> 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.
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.
Such meteorites fall to Earth even today. Their interiors are often ice cold.
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.
> 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.
It doesn't demonstrate the existence of Shakespeare's works, but it's a building block that's good to know exists.
This is absolutely a good finding to have in your pocket.
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 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
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.
[1] https://www.wgtn.ac.nz/
[2] https://www.psi.edu/staff/profile/morgan-cable/
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
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.
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..