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PopeBrendicus t1_j8gtb4h wrote

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).

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ChemicalRain5513 t1_j8hf0j5 wrote

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?

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ringobob t1_j8hwmin wrote

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.

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JohnOliverismysexgod t1_j8hzmjk wrote

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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Ok-Dog-7149 t1_j8iukfx wrote

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

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Geobits t1_j8izxui wrote

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.

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Anarchaeologist t1_j8izjp5 wrote

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

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cesarmac t1_j8i79xk wrote

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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ChemicalRain5513 t1_j8izxli wrote

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.

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d0meson t1_j8ie6x7 wrote

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.

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Any-Broccoli-3911 t1_j8jx03e wrote

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.

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Lobo_Marvilense t1_j8ijzol wrote

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

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00notmyrealname00 t1_j8iw8y8 wrote

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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