The metabolic science is really cool. The conclusion that life arose twice requires you to buy that proto-cells that grew on these vents and needed those metallic surfaces to survive didn’t count as “life”. Then, free living cells, bacteria and archea, could maybe be argued as having independent paths as they plugged the gaps in their metabolism independently. Same DNA/RNA, same proteins. Same broad rules of metabolism. Just some alternate paths through chemical space to plug in the metabolic gaps and get free from metal surfaces.
To me, these are clearly not independent paths, but rather the branching of proto-life into two of the great kingdoms of life. It’s a stretch to call this two origins rather than a branching.
Then a couple billion years later, one of em ate the other, and rather than destroy it, they both started a symbiotic relationship, and we were off to the eukaryotic race. This is all the same web of life. Not two independent streams.
The paper claims LUCA doesn't count as life because it still depended on its environment to metabolize.
It's kind of interesting that there's parasites that arguably don't meet this definition either. Looking it up: Chlamydia can't reproduce independently; relies on its host's metabolism. Microsporidia can't make ATP on its own. Are these "life"?
The difference is more on survival. A closed loop metabolism is indeed a good boundary marker. Viruses would fail this. But many have “closed but for a few critical dependencies”, and the argument here is that when life depended on metals like this, it’s more critical dependencies than closed loop.
Somewhere in there is a transition. But it’s poorly defined, and so the argument can be there was a bifurcation of sorts.
People love to put things into neat boxes so that we can somehow reduce them to a single concept.
Unfortunately the real world is usually a bit more messy than that. This is one example that makes it pretty obvious that our model is a little bit overly reductive, and at least to me the "Is this life?" question seems to have an answer that is on a spectrum rather than binary.
> The conclusion that life arose twice requires you to buy that proto-cells that grew on these vents and needed those metallic surfaces to survive didn’t count as “life”.
Well, sure. For it to ever be possible to say "life arose more than once," one must decide where the boundary between life and non-life is. After all, every precursor of life arose all at once, in the Big Bang!
Hardly. There are nucleic and amino acids pretty much in every star system, we now know. But not during the big bang. Theres a lot of intermediate stages before stars are young enough to have the mix of chemicals to give rise to these precursor chemicals to life.
Its stages, but it’s a bit hard to say “early stage was a single origin, then we count each bifurcated radiation as a separate start point”. Why not call it convergent evolution, which it would be, over a very long time period?
> …one of them at the other,
The origin of life is as romantic as I’d hoped.
You would think there would be some isolated places where proto-life still exists for this to be true.
No, because conditions have changed markedly. For metals to act as catalysts, and replace some metabolic enzymes, they need to be in highly reduced conditions. This was true in early Earth, but about 2.5 billion years ago, we had the great oxygenation event, and over the next billion years free oxygen has gone up enough that you won’t find the reduced conditions where metal can take over the job of metabolic enzymes in much of Earth anymore.
That is, what sustains today’s life prevents new proto-life for forming. You need to have the fancy gadgets life has today to continue to survive and replicate on Earth.
Note though, it was other life forms that contributed to the great oxygenation event, too. This is all a continuous web.
Just curious, are there lifeforms today that rely on these metals to live in anaerobic environments? Maybe the hydrothermal vents that are talked about?
Do you think complex life could develop (perhaps by moving backwards) in a way that they rely on an anaerobic metal-rich environment?
I guess the oxidation event maybe was necessary for life to develop enzymes (since there wasn't sufficient evolutionary advantage for it to develop in an anaerobic environment?) but maybe something could go backwards? I'm just curious if there might be advantages for live in that sort of environment.
There are actually quite a few environments on Earth that are time capsules / have little ship bottles of very different life inside of them. For example, the Movile cave, https://en.wikipedia.org/wiki/Movile_Cave
It's my dream to find one of these sites. I think there are quite a few locations out there yet to be discovered.[1] https://en.wikipedia.org/wiki/Dissimilatory_metal-reducing_m...
[2] https://en.wikipedia.org/wiki/Sulfate-reducing_microorganism
There could be deep subsurface microbes that are exposed to both pure metal and anoxic conditions that are similar, but note, it’s not “metal or protein” for catalysis. Many protein catalysts have metals incorporated.
What proto life did, it seems, was completely depend on metal surfaces to speed up some reactions. But that’s messy. The same metal can’t distinguish different components, so there would be competition for these surfaces, even within the same “cell”. That’s not ideal.
Enzymes are much more specific. You can actually sequester different reactions. And once you have life that’s learned to do that, it will out compete any proto life like matter that may access such environments.
Anaerobic microbes have enzymes also. So don’t think that reducing conditions mean no enzymes. It’s merely that in reduced conditions, you have metal that’s not oxidized available for early life -like goo to make use of. Over time, once this life learns to make newer and newer enzymes, the need to be metal dependent went away.
Somewhat separately, you also had some of this lineage learn to photosynthesize, and that lead to bulk oxygen in the atmosphere, and that was initially catastrophic, then highly beneficial because oxygen based chemistry is way more energetic than anaerobic chemistry.
It would be wrong to think of either condition as “better” though. They’re different. They force different tradeoffs. And both demand fine balance and dependence on the environment, eventually.
Coacervates, liposomes, acetogenic precursors, etc are all commonplace and could be considered proto-life. Some scientists have even argued that viruses are proto life. Prions (misfolded proteins that can self-replicate) and plasmids (non-chromosomal DNA strands that play a major role in horizontal gene transfer) are also candidates for proto-life that blur the line between living and non-living
For what it's worth, metals are still critical catalysts all over biology, they just tend to be encapsulated in biomolecules.
I always found it odd that there's only one single origin of life point or even just a single common ancestor considered in history. Shouldn't entirely new life develop all the time on earth? I mean the ingredients and building blocks are still there, the environmental situation still should work out, like availability of water, temperatures, etc. We should see a constant emergence of new life all the time. Why would that process stop, just because some other life already exists? Maybe we just can't detect this, because whatever new life happens to appear —more or less— resembles life that's already there.
They're pretty sure the primordial environment was a hydrothermal vent in an anoxic high phosphorus soda lake with methane, ammonia, and UV exposure. Nowadays those lakes don't have the methane and ammonia, so that environment isn't there anymore. https://www.science.org/content/article/unusual-soda-lakes-m...
The surfaces of clay particles in these lakes have been dubbed "the primordial sandwich".
The early protocells were 'alive', they were self-replicating, but they required nutrients and metabolic processes that only existed near mineral surfaces and would starve if they drifted away. They had to evolve new enzymes to become 'free-living'.
So it looks like the LUCA was one of these early protocells with an incomplete metabolism.
But the enviroments that have the easy/free energy that would give rise to life is almost always contaminated with life competing for and consuming that chemical energy.
> Shouldn't entirely new life develop all the time on earth?
It's possible OoL requires some exponentially unlikely step. We wouldn't realize that because of observer selection: had the step not occurred, we wouldn't be here to be thinking about it. There's a huge complexity gap between the stuff produced in OoL experiments and the simplest known life.
It's also possible OoL requires conditions that no longer exist on Earth, or that only existed in the early Earth (or wherever life got started in the Solar System). For example, if it depended on the existence of short lived radioactive isotopes or free ammonia.
I'd imagine the bar for becoming new life is much higher now, because it requires finding a niche that isn't already filled by an existing organism or requires being immediately competitive with existing life.
It has to survive though in the sense that it has to live long enough for us to see it. If we think of life as "spontaneously" (roughly speaking) emerging from the right conditions reasonably rarely, it has to outcompete other existing life for some time. And then there's the chance that we might not recognize it as "new" at all.
A step further "novel" life (hence still simpler) made from the same raw materials as existing life would look exactly like decomposing existing life and be routinely scavenged for material.
The ingredients and building blocks aren’t there in the same way. Because life formed, those early ingredients are now transformed, as is the environment. This blocks new life of the type that formed 4 billion years ago from forming again.
Indeed, all species branch out from that one universal common ancestor that was the first free living successful cell.
Put another way: forming life isn’t easy at all. And once it forms it changes conditions to suit its continuation, not to allow new life to form.
Life is vastly faster than random chance at producing more life. So living things go fill niches faster than random chance can use those niches to produce new life.
> Maybe we just can't detect this
Probably this. How would we know what such 'proto-life' (perhaps even just some self-replicating soup of chemicals, no cell wall) would look like? Where to find it? How rare its occurence? Etc etc.
Scientists might not even recognise it if happened right in front of them.
I'd put my money on coming up with a more general definition of "life", and then looking for short(est) pathways from "soup of random chemicals" to "something in there that replicates (parts of) itself".
Doesn't need to look like life as we know it, as long as some elements of "self-organising structures, something being replicated" are there.
> Shouldn't entirely new life develop all the time on earth?
The fact that it doesn't is a pretty simple solution to the Fermi Paradox.
The building blocks will be immediately consumed by existing life. And that's just one way in which the world is radically different from the one in which life arose.
And life may have arisen from a very low probability set of circumstances ... there's no reason to expect it to be happening all the time.
>ike availability of water, temperatures, etc. We should see a constant emergence of new life all the time. Why would that process stop,
Anything that's so agreeable to abiogenesis that life might spontaneously manifest, is actually pretty tasty for things already alive. They swoop in and eat it before it gets started. So, I suspect that even what the article says isn't that they both arose in the same place, but in different places separated by distance, time, and/or environmental barriers.
Hash competition from life might cause them to go extinct, and even if it happens again it just gets out-competed to extinction fast.
It could be happening on my kitchen counter right this very second. But my kitchen counter, despite a recent cleaning, is absolutely lousy with microorganisms. So the new proto-life is immediately starved or more likely eaten by existing life. There's very few places on Earth that has not been colonized by some sort of life so there's very few places a new form of life could form and succeed long enough to itself grow and spread without being starved or eaten.
Maybe, or maybe it was eaten into extinction.
Geology over large time-scales is profoundly unforgiving.
the Great Oxidation Event caused all kinds of crazy stress = crazy mutations/adaptations where one eventually started our path
* https://en.wikipedia.org/wiki/Great_Oxidation_Event
one of my absolute favorite PBS Space Time on the subject
* https://www.youtube.com/watch?v=abvzkSJEhKk
"proto-cells that grew on these vents and needed those metallic surfaces to survive didn’t count as “life”"
What makes that argument extremely weak is analogies with contemporary obviously living animals.
For example, humans are not alive, because we get 100% of our vitamin D ascorbic acid by scavenging from the environment, along with a handful of other animals that presumably evolved in an extremely vitamin C rich environment. If any animal, including humans, ever evolve a new ability to internally synthesize vitamin C from glucose like every other animal, then given that there were non-synthesizer animals in their ancestry who we arbitrarily define as not-alive aka dead, then we could say that life evolved twice.
Note that humans could be defined as dead because we can't synthesize our own oxygen and have to scavenge 100% of it from the environment using lungs and so forth.
If you pencil whip the English language hard enough, anything with lungs or stomachs is not alive. A similar line of argument would lead to all saprophytes not being alive, which is pretty ridiculous. Wood eating mushrooms are not alive because they rely on the environment to provide all their wood dietary needs. Yeah OK whatever.
No it’s not that simple. We don’t fall dead the moment we don’t get vitamin D. We can stay alive long enough to get more.
That wouldn’t have been the case in these early beings, that were simply not capable of doing anything without these metals.