Radical Study Suggests Life on Earth Arose Twice
sciencealert.com
sciencealert.com
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.
* https://en.wikipedia.org/wiki/Great_Oxidation_Event
one of my absolute favorite PBS Space Time on the subject
The fact that it doesn't is a pretty simple solution to the Fermi Paradox.
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.
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.
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.
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.
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.
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.
We don't know where exactly viruses came from, but one of the leading theories is actually that they are the descendants of bacteria which outcompeted other bacteria. When a parasitic bacterium sheds more and more of its own metabolic capabilities, because it's more efficient to steal those abilities from its host cell, it evolves in a way that looks more and more like a virus.
"More evolved" or "more advanced" in this case doesn't mean "bigger" or "more complex". You can say viruses are equally evolved as bacteria, meaning they've spent equally long being optimized for their ecological niche.
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.
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.
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.
> Just curious, are there lifeforms today that rely on these metals to live in anaerobic environments? Maybe the hydrothermal vents that are talked about?
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
Life in the cave has been separated from the outside for the past 5.5 million years and it is based completely on chemosynthesis. Due to its extreme environment, access to Movile Cave is strictly controlled, and a limited number of researchers have permission to study its conditions.
[1] https://en.wikipedia.org/wiki/Dissimilatory_metal-reducing_m...
[2] https://en.wikipedia.org/wiki/Sulfate-reducing_microorganism
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.
That wouldn’t have been the case in these early beings, that were simply not capable of doing anything without these metals.
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!
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?
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"?
Somewhere in there is a transition. But it’s poorly defined, and so the argument can be there was a bifurcation of sorts.
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.
Presence of metallic catalysts is just an environmental factor. Not counting the organisms that can't live without them as life would be as not counting as life something that can't do metabolism without liquid water.
Life at time of LUCA just had a bit stricter environment requirements, but it should still be counted as life.
So I wouldn't read this as discovering that life evolved twice. Life just evolved a hack for dealing with environments without metallic catalysts twice.
No, it isn’t quite that. For it to count as “environment” the organism must be able to survive for at least a time without it.
The issue here is, the metal wasn’t a nutrient. That would be fine and exactly like it is for all life now.
Instead the metal was the anchor. If an organism needed to grow on it to enable half its metabolism, it is at the least very distinct from current life.
The only issue with the “two origins” claim is both lineages, bacteria and archea, come from this, and even with an open metabolic chain, you already had the nucleic acid function etc all sorted out, and common between both kingdoms.
So it’s a stretch to say there were two origins to life, but not that this proto life is distinct from modern life. That we need things from our environment is not the same as what they found about proto life in the vents.
How long can a cell survive without liquid water? It literally enables almost all of the chemistry inside the cell.
Cell requiring a specific metal to be present is not very different from cell requiring for liquid water to be present.
Initially life started in favorable conditions, then spread to less favorable ones. Lack of metal catalyst around was the initial less favorable condition. At some point lack of liquid water was one. But eventually life spread to various very dry or cold places because it found workarounds for environment infeasibilities.
Maybe in 5 billion years life that can't survive without liquid water around and can't substitute it with self-made polar solvents and thus is stuck to surfaces of very few, very particular planets is going to be considered proto-life.
Depends on the cell, but it’s not instant death. By definition, a cell is a membrane with some water inside it.
Sure, move that cell to totally dry conditions and most will die. But not all, by any means. Bacterial endospores last millenia without water. Tardigrades can do years.
This isn’t quite the gotcha you think it is.
The metal use for multiple catalytic steps is distinct. The paper isn’t wrong about that at all. Trying to prove the closed loop metabolism of modern life is secretly open loop isn’t going to work because it isn’t open like that. An organism can survive without constant contact with any of its components. Sometimes not for very long, but nothing alive today is as dependent on something external as these proto cells were on reduced metal.
The origin of life is as romantic as I’d hoped.
Should be "Life left mineral substrate at least twice" or some such. The research is interesting, but they're playing word games in the telling of it by saying the most recent common ancestor of all life wasn't alive (because it was dependent on a mineral surface), but two of it's children gave rise to lineages that were.
> “When we react phosphite, a form of phosphorus that naturally occurs in hydrothermal vents, with organic compounds, we get metabolic phosphorylation reactions overnight in water. Phosphite and palladium replace ATP and enzymes; it’s amazing, and it makes early evolution a lot easier to grasp” says Schlikker.
As far as I know, there are no palladium enzymes ... checks ... ok, no _natural_ ones (that we know of). Which is interesting, as other enzymes in metabolism that use metals seem to have 'adopted' the metal(s) as a cofactor - like nickel, iron, molybdenum, even vanadium in at least one case.
Anyway, it does provide a nice reason that bacterial and archaeal cell membranes are different.
Free-living cells arose twice would be more accurate.
I heard a good way to describe LUCA is "half-alive", with about 40% of its metabolic reactions driven by the mineral substrates in the pores it lived in, and lacking a complete cell membrane.
I can't help but speculate LUCA would have some simple membranes to cover the "windows" of the mineral pores and keep vital molecules inside - a tiny pore-dwelling metabolic network.
The question of "how much independent metabolism counts as life" is looking a lot more like the question of "how many facial hairs make a beard"
I wonder if LUCA was not a single cell, but many different populations in different hydrothermal vents, exchanging genetic material wrapped by accident in the remains of the cell membranes as the host cells die and are ejected from their vents.
Perhaps the missing post-LUCA metabolic enzymes evolved by accident from proteins recruited simply to concentrate the required metal ions that are scarcer and ever more diluted the farther from the black smokers you get. Free living was merely a happy bonus effect.
* https://en.wikipedia.org/wiki/Formation_and_evolution_of_the...
I assume that the difference here, is that it went completely to zero, before restarting. The other times, there was a bit clinging on, that seeded the restart.
The reality we will never be able to replicate creation of life nor find life on other planets (except via contamination). it's why we've never gotten any closer. and i'm not even religious
So, either there's a filter that's blocked interstellar colonization... or it has occurred already, and we just aren't aware of it (some sort of dark forest thing / we are being secretly watched by an extraterrestrial civilization).
(This is a haunted galaxy either way!)
There's no reason to believe a civilization is capable of million year projects.
Saying "I have a bad model but there's some unknown Great Factor which would make it a good model" isn't very convincing.
There are myriad factors: the biological challenges of space travel constitute a long list in itself; the economics and politics involved (ROI on any useful timeframe for interstellar travel is zero); the engineering challenges (the vast majority of interstellar travel attempts will result in the death of all crew somewhere in interstellar space); the fact that over million-year timescales, species evolve and change - humans are only around 30% of a million years old.
We seem to make gradual progress in investigating like this article and recently there was stuff on how RNA could self replicate https://youtu.be/EhPgu0I8yaY
I'm your distant ancestooor
I have some news for you
Yes, they think life came once before
https://en.wikipedia.org/wiki/WASP-39b
There are astronomers actively working on minor component, more biologically interesting spectrographs like chlorophyll rather than spectrograms of carbon dioxide. That'll be harder to detect and limited to shorter ranges.
At some point, probably very soon, like less than a decade, we'll be able to definitively state that we have atmospheric data in an onion layer shaped shell where we have unequivocable proof that out to X lightyears from Earth there's no planetary scale chlorophyll higher than a minimal level aka there's no earth-like plants on that planet. That shell will likely expand over time. Or, perhaps we will find a forested, or at least algae covered, planet, some light years away, which would be very interesting indeed.
The question is rapidly changing from a purely philosophical belief to scientific observation, like right now, in real time, in the 2020s. What a cool time to be alive!
This follows old, old stuff from radio astronomy along the lines of how far away could a 1960s radio telescope realistically detect life on earth. The answer IIRC was not very far LOL. But there's been a lot of progress in radio astronomy, etc.
With respect to fermi filters etc people need to pay attention to how far away the Earth can be detected using radio telescopes. That distance has imploded since the end of analog UHF TV broadcasts. We still broadcast absolute swill, in fact more than ever, but digital detection range is much lower than analog AM carrier detection range from analog TV. The Earth has, to some extent, recently gone radio-quiet, which is interesting because we are still here, in fact more of us than ever. So WRT fermi filters of not being able to detect civilizations, disappearance of 1950s/1960s signals does not necessarily imply disappearance of civilization. Another example, if any aliens are watching the high altitude freon contamination of our atmosphere they're likely really confused right about now.
But high level life was likely a series of complex accidents that is not reproducible or would be radically different than us
One of my absolute favorite PBS Space Time on the subject
What is the basis for this assertion?
* https://www.science.org/content/article/lab-created-spudcell...
somewhere among 2 TRILLION planets in our galaxy there is a planet with enough atmosphere and magnetosphere to protect it from space radiation so there is likely bacteria
but complex life far more difficult and unlikely, very rare, as explained in the PBS Space Time I linked above, the "Cambrian Explosion"
* https://en.wikipedia.org/wiki/Cambrian_explosion
if there are viruses and fungi out there however, they could mutate eventually with enough permutations and outside stressors
that video explains the huge leap forward with DNA vs simple protein patterns
> somewhere among 2 TRILLION planets in our galaxy there is a planet with enough atmosphere and magnetosphere to protect it from space radiation so there is likely bacteria
I reject this conclusion; it certainly isn't justified by the links you provided.
why would Earth be that incredibly unique?
it's even plausible Earth was accidentally seeded by panspermia (bacteria on comets)
Your reversal of burden of proof is a red flag that you don't have a good argument.
IMO, it is quite plausible that OoL is extremely unlikely and that our solar system is the only place where life occurs in the visible universe. Not proved, of course, but the possibility is by no means unreasonable.
but it's pointless to go any further I guess as it's getting outside science
the weak anthropic principle can't be falsified so it cannot be argued
I don't think we'll ever hear from "ET" but I do think it's perfectly plausible to find single-celled or simple bacteria elsewhere someday (ie. Europa, comet or asteroid)
But I'm not doing that -- I'm saying it's a possibility that is consistent with evidence.
The claim that life is common is different. For that, you really need to present an argument that life being uncommon is ruled out.
In your last sentence there you've retreated from "life is common" to "it's plausible life is common". Sure (within the constraints of the Fermi Argument, but that has uncertainties.)
I think the answer to the question is easy if we consider quantum mechanics. It says every possible random event manifests in some universe. This means that an event or combination of events, no matter how incredibly unique, manifests in some universe.
Imagine the very first cell. Imagine that all the particles of that cell coming into the exact spatial location by pure random chance. It is a chain of incredibly random events. But it does not matter. QM says that it manifests in some universe.
So, We are just in one such universe. Of course, there might be universes where this incredibly random event have manifested more than once. But since then number of such universes are minuscule when compared to the number of universes where it happened only once, there is an overwhelming chance that we, as one conscious species, finds ourselves in a universe where life originated only once.
In the same manner, there could be universes where an entire brain assembled itself purely randomly. But the number of such worlds are a small fraction of the worlds where a single cell formed, and followed the relatively simple procedure of natural selection and end up as beings who can ask such kinds of questions.