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Radical Study Suggests Life on Earth Arose Twice

sciencealert.com

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Re: Radical Study Suggests Life on Earth Arose Twice

#81

Post by Rigdanir »

I find this fascinating. LUCA clearly predates some pretty core, basic metabolic capabilities, and yet nucleotide metabolism is complete. This seems to indicate that LUCA and its progenitors were confined to their hydrothermal vents and that the cells could not survive beyond due to the missing metabolic networks.

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.

Re: Radical Study Suggests Life on Earth Arose Twice

#82

Post by fwip »

ch4s3 wrote: post #6
lanstin wrote: post #3

Earlier quoted context omitted.

They aren’t saying two totally different independent life creating event, they are saying that the earliest life depending on some external chemicals for parts of what is now covered by metabolism, and the tree of life diverged before those metabolic paths evolved inside the organism, so not totally the same emergence of life twice, but more stuff that reproduces and evolves but doesn’t meet modern standard for life.

The science alert article should make this more clear, as its easy to get that impression.

Well, it's Science Alert - not exactly a bastion of level-headed reporting.

Re: Radical Study Suggests Life on Earth Arose Twice

#83

Post by randomImmigrant »

neuralkoi wrote: post #80
randomImmigrant wrote: post #25

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 metaboli…

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.

Re: Radical Study Suggests Life on Earth Arose Twice

#84

Post by randomImmigrant »

tshaddox wrote: post #76
randomImmigrant wrote: post #25

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 metaboli…

> 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?

Re: Radical Study Suggests Life on Earth Arose Twice

#85

Post by randomImmigrant »

VLM wrote: post #74
randomImmigrant wrote: post #25

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 metaboli…

"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…

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.

Re: Radical Study Suggests Life on Earth Arose Twice

#86

Post by drdeca »

wao0uuno wrote: post #79
theodorejb wrote: post #5

[flagged]

And where did that god come from? Primordial soup full of magic and stardust? The idea of life starting by chance is completely absurd to you but somehow a god that just came out of nowhere is perfectly reasonable.

I don’t think what you are pointing at is a real issue.

Something exists. Therefore, on of the following 3 must hold: “one or more things exists or have existed which were not a consequence of another thing existing”, “an infinite regress of things existing as a consequence of other things”, “a cycles of consequences”.

The purported absurdity of life arising by chance is not about life existing, but about it arising by chance as a consequence of other non-living things.

The idea that god coming from nothing is absurd, well, that absurdity seemingly has to apply somewhere, as all 3 cases of the trichotomy above seem around as absurd? Eventually something has to be without explanation, whether it be a thing or a chain or cycle of things.

Or, were you not aware that most people who believe that God exists believe that God is the first cause?

Apparently you weren’t aware of that, because you said something about magic and stardust??

Re: Radical Study Suggests Life on Earth Arose Twice

#87

Post by randomImmigrant »

foota wrote: post #73
randomImmigrant wrote: post #57

Earlier quoted context omitted.

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…

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…

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.

Re: Radical Study Suggests Life on Earth Arose Twice

#88

Post by andrewflnr »

mycall wrote: post #34
randomImmigrant wrote: post #25

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 metaboli…

You would think there would be some isolated places where proto-life still exists for this to be true.

For what it's worth, metals are still critical catalysts all over biology, they just tend to be encapsulated in biomolecules.

Re: Radical Study Suggests Life on Earth Arose Twice

#90

Post by areoform »

foota wrote: post #73
randomImmigrant wrote: post #57

Earlier quoted context omitted.

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…

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…

     > Just curious, are there lifeforms today that rely on these metals to live in anaerobic environments? Maybe the hydrothermal vents that are talked about?
Yes! There are a few interesting variants called, "dissimilatory metal-reducing microorganisms"[1] and "sulfate-reducing microorganisms." They're a class that's being studied as a model for non-Terran life.

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.
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

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