I think anything novel must compete with well adapted, established organisms using a limited set of resources that the existing organisms recognize as food.

I believe there must have been more than one abiogenesis in the beginning, but only one was ultimately successful. Kinda like how there were many branches of Homo, but we are the only ones still around. I can't picture a scenario where one chance encounter leads to life as we know it. I can picture a situation where the conditions were conducive for life, many were nearly there, several would be defined as life now, and only one found success and dominated.

Not my area of expertise so someone may correct me later on, but the prevailing theory is that all life is descended from a single abiogenesis event, mainly because any life we have found evidence of has functioned exactly the same (well, basically) as things alive today. No one sticks out enough to say "yeah, that's funky, that doesn't work the same as everyone else"

I highly recommend Life's Edge by Carl Zimmer for an interesting read on this topic, because a lot of the questions you're asking depend on the very-much-disagreed-upon definition of "life." There are still scientists looking for signs of abiogenesis, in labs and in the field (particularly around volcanos, hot springs, thermal vents, etc, because that's what Earth used to be like).

No. 2 reasons.

1. Life is a winner take all phenomenon. Once life has overtaken and adapted to an ecological niche, it would be very hard for something new to evolve there that was better adapted

2. There is a hypothesis that the first chemical steps in abiogenesis required an earth with no or low oxygen. Nick Lane talks about this in some of his books (highly recommend)

what about hydrothermal vents?

This is what Nick Lane talks about in his books. Hydrothermal vents were very likely important in abiogenesis but only in an ocean with a different chemical makeup than today

It isn't clear that there was a specific entity that could be widely considered alive that suddenly appeared one day at all.

There could have been millions of years of complex processes going on which was sort of a gradient from "definitely not alive" to "definitely alive".

Microbes can accept genetic information much more readily than animals do with unrelated forms, and all sorts of genes have probably disappeared in the last billion years. How would one define not ancestral to modern life vs ancestral.

Even if all the genes of some creature are no longer extant, they could arguably have shaped the evolution of genes that still are,so there is still some remaining influence.

This was Lamarck’s thesis. That the reason we see life at different levels of complexity is that life originates continually, then evolves, so lower life forms of life are members of younger lineages. Bacteria would be only slightly removed from the latest origination, for example. That said, no, it is not a current hypothesis of Biology that life is continually emerging from non living precursors. We haven’t observed any extant natural ecosystems that contain “proto-life,” nor something transitional between life and non-living potential precursors, nor chemical environmental conditions similar to those surmised to have existed 3.5 billion years ago on earth.

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Can't it be that this happened multiple times, but that the resulting biochemistry was so similar that we can't tell? If the ocean was filled with particular building bricks, the optimal results would all look similar right?

Viruses require, by definition, host replication machinery to reproduce. They are completely inert otherwise. So... they could not have come first... or at least, not vira as we currently understand them.

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Did it happen more than once? Probably, however, it would have been very similar in composition. There would also be practically no evidence of any additional lines as only the dominant line remained.

Is it still going on today? Most likely not. There's too much life around, and to a lot of organisms, the components required for abiogenesis look tasty.

It’s possible in some extreme environment that could have been the norm billions of years ago here on Earth—but a life form from scratch would have to compete with evolved organisms soon enough and would likely end up as food for some other organisms.

Hard to imagine how that might work in the overall landscape of evolution. Let's assume there were two successful evolutionary lineages that began from two separate abiogenesis events. Do you expect both lines to produce their own, say, bacteria? Plants? Animals? I think what you would expect, hypothetically, is that one line produced its own kingdoms of life, and the other produced its own kingdoms of life, and they'd be unrelated.

So, like, you'd have fungus over here and plants over there, but they'd be entirely unrelated. And that's not what we see. They are related.

The other alternative is that these simple forms of life can intermix. In which case, it makes less sense to think of it as happening multiple times, and more sense to say they were so undifferentiated as to be the same thing. This is sort of a chicken and egg problem. If the conditions necessary to spawn life essentially produced a population, rather than an individual, then I don't know that we'd be able to tell the difference without seeing it in action. And the result would be that we're descendents of all of that life, rather than a single moment of abiogenesis.

Intuitively, it would be surprising for two separate abiogenesis events to produce two forms of life that are that compatible, but perhaps such life is so simple that there's not enough complexity to actually differentiate them.

It's completely possible that abiogenesis (or Panspermia) did occur many times, but whatever organisms emerged as a result became extinct early on or are not preserved in the fossil record.

The places on earth right now (that we know about) where sterile but minimal materials for self replication machinery are available are very rare, and only on very specific parts of the Earth. Given that, whatever primordial soup pocket that does pop up now has to compete with any loose complex organic matter around it, so good luck to my little progenitors....

When I was a kid, I learned that any instances after the one that took would not survive because such instance would be the perfect food, so it would be gobbled up by the life already here.

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Not likely, it was a very very complex event that was highly unlikely but still probable. The event require a very specific set of circumstances and environmental conditions. Unless of course panspermia was the beginning of life on earth. Also highly unlikely but equally probable.

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Well i think he's asking about the possibility that ancestral biological structures might have been very similar. Like say ancient vacuoles maybe existing on their own and using RNA as a means of building other vacuoles. The RNA strands might have been extremely simplistic by today's biological standards.

Then you have other extremely simplistic structures that originated somewhere else, using RNA as means of doing extremely simple and menial tasks. Then these proliferate and eventually come into contact with each other and by coincidence form more complex relationships as single structures over time, kind of how the mitochondria is theorized to have become a part of the cell millions of years later.

When they combine maybe it would be difficult to determine that they were two distinct lines of life because they used the same means of relaying genetic information.

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This seems somewhat unlikely because of compatibility of chirality. Many molecules aren't the same as their mirror image (just like your right and left hands), and chirality is what distinguishes these molecules from their mirror image (a "right-handedness" or "left-handedness").

All life on Earth uses a set of compounds with the same chirality. Enzymes are built to catalyze reactions that exclusively produce the correct chirality of product. In fact, for some of these molecules, their mirror images are actually toxic.

In contrast, non-biological reactions generally don't have such a strict chirality preference. In general, you produce a mix of both "handednesses" in most reactions not involving something extremely selective like an enzyme.

So in abiogenesis conditions, the selection of our current chirality rather than a different one was likely due to chance. If it happened multiple times, it's unlikely that it would have given the same chirality every time.

I think number 2 is often overlooked. The oxygen catastrophe completely changed Earth’s environment. Oxidation tends to lead to a lot of water unstable molecules. It could be that for life to originally form you need longer more stable molecules and now the environment is just not conducive to the molecules being stable enough to start new life.

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As far as my knowledge goes, which is very little - earth had a reducing atmosphere early on in the development of life, which would make abiogenesis much easier by making the production of macromolecules more generally spontaneous. Instead, we now have an oxidizing atmosphere, making breakdown tend to be spontaneous.

Moreover, it’s possible that circumstances were never favorable for abiogenesis. Rare events do happen, after all, and if at some point the circumstances were truly favorable, then we might expect it to have happened more than just once in Earth’s history (or the history of all of the planets we’ve investigated for life). But we haven’t found evidence for multiple abiogenesis events.

Combining those two notes, although it certainly isn’t impossible that abiogenesis continues to happen every now and then, it was probably never likely, and may be even less likely now.

The abiogenesis "event" took billions of years to occur to get a single cell organism.

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Your first point reminds me of the Ediacaran biota, which appears to contain the earliest forms of multi-cellular life - before even the Cambrian Explosion. What's fascinating is that probably 99.9% of these species died out 600 million years ago, with that small fraction surviving into the Cambrian to establish the forms we know today.

This would seem to make some assumptions about relative proximity between the two.

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This may be the simplest answer.

We may just not have been able to observe things long enough to make the determination of how the initial event took place. Even if we ran tests in the perfect environment and were able to replicate those tests 1000 times faster, it would take us a million years to see a single success that took a billion years. What if it happens more than just once (say, a thousand times) in that time period? That's still 1000 years to observe success.

It wasn't until the late 19th century that we could even observe cellular division, so at best we've been at it for 150 years. Not to mention that we haven't been looking/testing for it for very long. We may have a long way to go.

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Do you have an area in mind that this might happen? Every environment on Earth that's suitable for organic life's survival seems to already be swarming with microbes

Clearly all the dna of eukaryotes is so related that it cannot be due to chance. But could it be that archae and bacteria formed from separate abiogenesis events?

Or could eukaryotes have formed multiple times? We know that encapsulation of bacteria to form organelles has occurred at least twice, namely for mitochondria and for chloroplasts. Could it be that different eukaryotic kingdoms have mitochondria that are not related?

>If the conditions necessary to spawn life essentially produced a population, rather than an individual, then I don't know that we'd be able to tell the difference without seeing it in action.

Yes this is essentially what I meant, the question whether all life comes from one single cell, of if at some point the conditions were such that many cells formed that were very similar, maybe even with similar dna that was being copied, floating around.

If they were close in time, sure. It's hard to imagine a biogenesis event now, for example, because existing life is so ubiquitous that it'd have a hard time competing against everything.

It is possible.

We have not observed it. If it does happen, it happens in small scale and the new liveforms don't spread (possibly because they can't compete with established lifeforms and get eaten).

We have no idea what is the probability of abiogenesis for a given environment.

There is no evidence that the ocean was ever filled with amino acid and nucleic acid. Also, there are a lot more possible amino acids and nucleic acids than the 20 amino acids and 5 nucleic acids we use. We would expect living beings coming from a different abiogenesis to use different ones.

The problem is that any source of low entropy energy will immediately get colonised by sophisticated organisms that that have billions of years of development over a bunch chemicals that have coalesced in a crack in rock or whatever. The origin of life was probably in very slow, unreliable, marginally-alive processes.

Those startups needed to be the only show in town to survive. They would now competing against modern organisms that have been through zillions of improvement cycles. It's like a F-18 versus a wooden stick.

Agreed, the Ediacaran period was a frontrunner for MCL. Shame we know so little about the transition from that period

What suggests that there was not just a single but many a-biogenesis events. What makes you favor that over a single one other than that it could be possible?

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