Asteroid fragments upend theory of how life on Earth bloomed
49 comments
·March 1, 2025disqard
twothreeone
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
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.
dguest
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.
marcosdumay
> 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.
close04
> 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.
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roxolotl
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
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.
lupusreal
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.
miramba
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?
wjnc
Couldn’t there exist a chirality filter on earth?
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bloomingkales
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.
madaxe_again
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
An explanation is required for why that selection occurred here, and not in whatever biosphere from which this one was panspermically inseminated.
metalman
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
The term for this process is "racemization".
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pfdietz
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.
gunian
[flagged]
zkmon
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
The why explains itself. Cells that do not divide and reproduce disappear.
jhrmnn
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.
datadeft
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.
drbojingle
Evolution is a description of what we see happening in animals over time. That's all. This is about the formation of life.
datadeft
"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
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
I think “how did non-living matter become alive” and “how do populations of organisms change over time” are two very different questions.
8bitsrule
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.
JohnMakin
Uh, no? And I think you’re confusing abiogenesis with the process of evolution - they are different processes.
krapp
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
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
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.
> 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.