[HN Gopher] Asteroid fragments upend theory of how life on Earth...
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Asteroid fragments upend theory of how life on Earth bloomed
Author : bookofjoe
Score : 93 points
Date : 2025-03-01 12:44 UTC (4 days ago)
(HTM) web link (www.nature.com)
(TXT) w3m dump (www.nature.com)
| bookofjoe wrote:
| https://archive.is/Zw2gh
| disqard wrote:
| > Not only does Bennu contain all 5 of the nucleobases that form
| DNA and RNA on Earth and 14 of the 20 amino acids found in known
| proteins, the asteroid's amino acids hold a surprise.
|
| > On Earth, amino acids in living organisms predominantly have a
| 'left-handed' chemical structure. Bennu, however, contains nearly
| equal amounts of these structures and their 'right-handed',
| mirror-image forms, calling into question scientists' hypothesis
| that asteroids similar to this one might have seeded life on
| Earth.
| twothreeone wrote:
| Hm, why would chirality need to be a consequence of the
| panspermia hypothesis? I thought the mission defined "necessary
| ingredients for life" as any bio markers that might have seeded
| a primordial soup on Earth.
| tomohelix wrote:
| One way to interpret the results here is that all the
| building blocks of life can naturally be formed right here on
| earth or anywhere that has conditions similar to where Bennu
| came from.
|
| The fact that the components on the asteroid is racemic meant
| or heavily suggested that they were formed using non-biogenic
| means. And if so, it also means that Earth could have had the
| same thing happened a long time ago, leading to the seeds of
| life.
|
| tl,dr: this discovery weaken the panspermia hypothesis.
| lupusreal wrote:
| Abiogenic synthesis of "primordial soup" is fairly straight
| forward, see the Miller-Urey Experiment. A soup of random
| amino acids and whatnot might be created in a number of ways
| on Earth, so it's a stretch and not very interesting to
| suppose that such soups didn't exist on Earth and were
| brought in by space. The interesting panspermia hypothesis is
| that actual life came down from space. Finding amino acids in
| space could be evidence for that, but if the stuff found in
| space is mixed chirality that undermines those chemicals as
| evidence of life in space. Mixed chirality implies a mundane
| abiogenic origin.
| wjnc wrote:
| Couldn't there exist a chirality filter on earth?
| XorNot wrote:
| The question is "how?" though. The chirality filter on
| Earth is basically Earth-life: it almost ubiquitously
| creates left-handed amino acids. But all known chemical
| ways of doing this produce racemic mixtures of both
| types.
|
| If we found say, a high pressure synthesis method which
| was heavily biased chirally, then that would be good
| evidence but none has been discovered.
| nkrisc wrote:
| Is there any evidence of one or such a theory?
| wjnc wrote:
| I am a total noob in chemistry and Claude said that it
| was a great question, but the answer were quite unclear
| about the feasibility. Mainly theoretical filters on lab
| scale. So that led me to put forward the thought.
| jerf wrote:
| Nobody has found or even so much as proposed a very good
| one. There's a bare handful of reactions that can tend to
| amplify chirality, but most uncontrolled chemistry
| (including things like Miller-Urey) produce a
| biologically-useless random high-entropy mix, and it is
| fairly unclear that these handful of reactions, which
| aren't even necessarily obviously useful ones and require
| some fairly special conditions, could possibly overwhelm
| the entropy of all the other reactions blasting out
| random combinations of things.
|
| AFAIK there isn't even a known way to start with "normal
| chemicals" and produce highly-chiral reactions reliably
| in the lab. We get all our chiral molecules by extracting
| them from biology.
| miramba wrote:
| These findings show that biochemical compounds, once
| thought to be fragile and denaturate quickly in non-earth
| conditions, can apparently survive space conditions for a
| long time, even in universe metrics, so they could travel
| far. If they can, maybe cells can too. But that doesn't
| mean it's likely to find actual life on a random asteroid.
| Of course there is equal chirality in lifeless conditions.
| The ultimate question is: How did the first cell came to
| be? Everything after that seems explainable, if not
| predetermined. But that the first cell just randomly
| happened in the primordial soup - that looks extremely
| unlikely, yet it's the best explanation so far. If cells
| could travel on asteroids, it's (equally? Less? Who could
| tell?) likely that the first cell just dropped here,
| intentionally or otherwise. Which would put the question of
| creation just to a different time and place. Somewhere in
| the universe, billions of years ago, life happened. Maybe
| it spread through the galaxy. Maybe sometimes a life
| carrying planet explodes, spreading asteroids with cells.
| Maybe some of them drop on planets with the right
| conditions. Given enough time, how unlikely is that as
| compared to random creation here?
| dguest wrote:
| There's a weak connection, but to me it reads like clever
| marketing.
|
| Actually _finding_ chirality in space would be extremely cool
| in that it would mean one of two things:
|
| - the panspermia hypothisis is correct, or
|
| - some non-biological process creates chiral molecules.
|
| Physics itself has plenty of chiral processes, but they only
| show up in the weak interaction. As the name implies, the
| weak interaction is really really weak and essentially
| doesn't exist on the energy scales of molecular interactions.
| So chirality would be a bit of a smoking gun for panspermia.
|
| On the other hand, _not_ finding chirality just means we don
| 't have a smoking gun. There might be another asteroid flying
| around that is 100% chiral, or maybe 50% of them and we were
| just unlucky.
|
| The briefing joins the point about chirality with evidence
| against panspermia, but really that might miss the point.
| Chiral or not, abundant amino acids in space means that one
| of the many steps to create life is relatively simple. If we
| could show that every subsequent step is simple that would be
| a big blow against panspermia. But in that case ruling out
| panspermia would be pretty cool, since it would suggest that
| life exists everywhere.
| close04 wrote:
| > the panspermia hypothisis is correct
|
| What I don't understand is why would chirality and
| panspermia be so tightly linked.
|
| The data right now still leaves every option on the table
| just because having any ratio of chiral molecules doesn't
| _have_ to define how _life_ evolves. It can 't answer
| whether those molecules formed on Earth or hitched a ride
| on an asteroid, or life itself formed here or was brought
| here.
|
| We can assume that in a soup with balanced proportions of
| each chirality, the left handed molecules created a self
| replicating mechanism (some definition of "life") first or
| faster than right handed molecules, either accidentally or
| because some yet undiscovered advantage. Whether this
| happened on Earth, or was brought to Earth by one or more
| of the millions of asteroids is hard to prove.
| dguest wrote:
| That's a good point. You also need consistency in the
| chirality on asteroids (also with earth).
|
| If we find one asteroid with chirality that _doesn 't_
| match earth, it's good evidence that self replication
| just happens spontaneously rather than being seeded.
|
| If we find only one asteroid with one chiral molicule
| that _does_ match earth, that supports panspermia very
| weakly: it still might just be random chance. But
| multiple matching molecules, on multiple asteroids,
| starts to seem like evidence for a common source.
|
| On the other hand: If we find multiple molecules with
| matching chirality, on multiple asteroids, and _none of
| them match with earth_... well, we should probably start
| preparing for the invasion.
| marcosdumay wrote:
| > There might be another asteroid flying around that is
| 100% chiral, or maybe 50% of them and we were just unlucky.
|
| The more asteroids we look and not find any asymmetry, the
| more evidence we have that life never existed on any of
| them.
| roxolotl wrote:
| I don't know a ton about how chirality works. Couldn't it
| just be that half(or some number) the asteroids contain left
| handed and half contain right? We only have a sample of one.
| Or is there something fundamental about left handed molecules
| that gives us reason to believe that if we see right handed
| ones once we would rarely see left handed ones in similar
| disconnected systems?
| jcranmer wrote:
| Chirality means that there is a mirror image of a molecule
| that cannot be twisted into the original shape, despite
| being structurally identical. Due to the particular ways
| molecules tickle each other in living organisms to do
| interesting things, that means that the mirror image
| (racemate) of a molecule does something different.
|
| In chemical synthesis, most (but not all) processes tend to
| preserve chirality of molecules: replacing a bunch of atoms
| in a molecule with another set will tend to not cause the
| molecule to flip to a mirror image. If you start from an
| achiral molecule (one where its mirror image can be rotated
| to the original), almost all processes tend to end up with
| a 50-50 mix of the two racemates of the product.
|
| In biochemistry, you can derive all of the amino acids and
| sugars from a single chiral molecule: glyceral. It turns
| out that nearly all amino acids end up in the form derived
| from L-glyceral and nearly all sugars come from D-glyceral.
| The question of why this is the case is the question of
| homochirality.
|
| There's as yet no full answer to the question of
| homochirality. We do know that a slight excess in one
| racemate tends to amplify into a situation where only that
| racemate occurs. But we don't know if the breakdown into
| L-amino acids and D-sugars (as opposed to D-amino acids and
| L-sugars) happened by pure chance or if there is some
| specific reason that L-amino acids/D-sugars is preferred.
| westurner wrote:
| "I Applied Wavelet Transforms to AI and Found Hidden
| Structure" https://news.ycombinator.com/item?id=42956262
| re: CODES, chirality, and chiral molecules whose
| chirality results in locomotion
|
| Do any of these affect the fields that would have
| selected for molecules on Earth? The Sun's rotation,
| Earth's rotation, the direction of revolution in our by
| now almost coplanar solar system, Galactic rotation
| roxolotl wrote:
| That's definitively helpful thank you. I guess I'm still
| surprised that this finding is being taken to mean left
| handed molecules couldn't have come from asteroids. If
| anything it seems to me to increase the likelihood of the
| panspermia hypothesis.
| jcranmer wrote:
| The reason this makes panspermia less likely is that the
| panspermia hypothesis would prefer to put the point at
| which all amino acids become L-amino acids before arrival
| on Earth, whereas the evidence is that the amino acids on
| this asteroid is before that point.
| roxolotl wrote:
| That makes sense. I'm just thinking statistically though.
| All we've proven is that some asteroids have R-amino
| acids. If it's a 50/50 shot you could easily find a dozen
| R asteroids because it starts to look really bad for it
| being a 50/50 split.
|
| I guess the reason it makes things more likely is because
| homochirality happens so aggressively that finding right
| handed molecules at all drastically reduces the odds of
| left.
| divbzero wrote:
| This is a good explanation of chirality but I think the
| parent meant to say _enantiomer_ instead of _racemate_ :
|
| - _enantiomer_ refers to each mirror image of the
| molecule. https://en.wikipedia.org/wiki/Enantiomer
|
| - _racemate_ refers to a 50-50 mix of the two
| enantiomers.
| https://en.wikipedia.org/wiki/Racemic_mixture
| madaxe_again wrote:
| I don't quite see how it disproves or undermines panspermia -
| surely if earth began with a racemic mixture of the building
| blocks, life could have started with either chirality (both
| being an unlikely scenario what with it vastly increasing
| complexity and therefore decreasing probability of evolution),
| and would then select for that chirality exclusively - so it's
| no great surprise we have ended up with a single-handed
| biosphere.
| throwanem wrote:
| An explanation is required for why that selection occurred
| here, and not in whatever biosphere from which this one was
| panspermically inseminated.
| bloomingkales wrote:
| I wonder how much deep sea research we'd have to do to find all
| the possible impact craters. There's gotta be lot of evidence
| at the source.
| metalman wrote:
| given the very deep time that these fragments have existed, It
| would be best to exhaust all possible or almost impossible ways
| that perhaps left handed enantomers could convert to right handed
| becuase 1 in a billion chances round up to every time....
| japaget wrote:
| The term for this process is "racemization".
| datadeft wrote:
| The evolution theory of origin of life just got a kick in the
| wrong spot?
|
| It is kind of weird how defensive is that crew. It is very much
| possible that life on Earth has extraterrestrial origins. I do
| not see why somebody would try to discard this idea.
| JohnMakin wrote:
| Uh, no? And I think you're confusing abiogenesis with the
| process of evolution - they are different processes.
| krapp wrote:
| I don't think you understand what "very much possible" means.
| It isn't a synonym for "I very much believe."
|
| We have actual evidence of evolution as a real and active
| process and can (and have) studied and mapped that process
| across species and across time - including in humans - and we
| find absolutely no evidence of nor the necessity for
| extraterrestrial influence anywhere.
|
| And even if some flavor of is assumed true for the sake of
| argument, that still wouldn't somehow negate evolution. It's
| entirely possible for life to have an extraterrestrial origin
| _and to have evolved_ on Earth after that origin, having first
| _evolved_ somewhere else.
| datadeft wrote:
| I am not saying it would negate evolution. I am saying
| origins of life could be extraterrestial and then life goes
| on a evolutionary process.
| literalAardvark wrote:
| This finding invalidates the idea that Bennu was seeded
| with molecules by biological life: biological life would
| have created chiral molecules, but the mix on Bennu is
| racemic, which suggests that the molecules were created by
| run of the mill geological processes and simply wouldn't
| require extraterrestrial seeding.
|
| Tldr the finding is that abiogenesis may be easier to get
| to than previously thought.
| pfdietz wrote:
| > Tldr the finding is that abiogenesis may be easier to
| get to than previously thought.
|
| It doesn't really mean that, though. We already knew
| synthesis of simple amino acids was pretty easy. Urey-
| Miller did that decades ago. Making the easy part of a
| multistep process easier doesn't make the whole process
| much easier.
|
| IMO, the rate-limiting step for OoL is later, when by
| some means the enormous complexity barrier is reached
| between abiotic stuff like this and the simplest self-
| replicating system capable of evolution. Of the latter,
| the simplest we know (the most stripped down cell) still
| contains billions of atoms.
| drbojingle wrote:
| Evolution is a description of what we see happening in animals
| over time. That's all. This is about the formation of life.
| datadeft wrote:
| "Historically, ideas on the origins of life have been mingled
| with evolutionary explanations. Darwin avoided discussing the
| origin of the very first species in public although he
| acknowledged the possibility that life originated by natural
| causes. Some of his followers adopted this materialistic
| position and advocated some sort of spontaneous generation in
| the distant past. Nevertheless, Pasteur's experiments were a
| major obstacle for scientific acceptance of the sudden
| emergence of life. The scientific study of the origin of
| life, established in the 1920s, required abandoning the idea
| of a unique chance event and considering a view of life
| emerging as the result of a long evolutionary process."
|
| https://evolution-
| outreach.biomedcentral.com/articles/10.100...
| drbojingle wrote:
| That's nice but there's still no reason to talk about
| things that reproduce and the origins of the building
| blocks of things that reproduce using the same word. Might
| as well say both the grocery store and the celery you
| bought are both stew. Or that shopping is cooking.
| User23 wrote:
| I think "how did non-living matter become alive" and "how
| do populations of organisms change over time" are two very
| different questions.
| 8bitsrule wrote:
| I wouldn't discard the idea, but OTOH, life -had to happen
| somewhere first-. That first clearly happened, and without
| extraterrestrial seeding. So that life either evolved, or ...
| because of the chemical makeup of the universe ... life is
| inevitable given the necessary conditions. This latter is a
| simpler and sufficient model.
| MarkMarine wrote:
| https://archive.is/3Wf9d
| observationist wrote:
| This is just a capture of the paywall, fyi.
| pfdietz wrote:
| This is interesting because the very earliest asteroids were
| warmed by short-lived radioactive decay. So, even small ones
| could have had interiors with liquid water. Their combined volume
| would have been very large, making them all potential sites for
| origin of life. Subsequently, impacts could have led to seeding
| of this life on the inner planets, including Earth and Mars.
|
| If these truly were the sites of OoL in our solar system, then
| that means life either originated early, before these asteroids
| froze up or dried out, or it wouldn't arise at all. This would
| vitiate the argument that because life appeared early on Earth,
| OoL must occur with high probability.
| zkmon wrote:
| Darwinism explains how the biological transformations and
| adaptations lead to racial diversity. However, the very goal
| which drives the adaptation, growth, reproduction or replication
| etc is not clearly explained, in my view. Questions like, why
| should the creatures have a root goal of growth and reproduction,
| why should a cell divide etc might need more thought. Was there a
| cognitive intention behind this adaptation? How did that
| intention originate and evolve? If the intention originated from
| inorganic material, does it still happen?
| bandushrew wrote:
| The why explains itself. Cells that do not divide and reproduce
| disappear.
| jhrmnn wrote:
| There are no goals in evolution. The most fit strain reproduces
| faster, eventually dominating other less fit strains. There's
| no purpose, it just happens.
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