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Then why isn’t there ANY examples of life simpler than a bacterium, which itself is insanely complex? Why does all life share the same genetic and amino acid co

Then why isn’t there ANY examples of life simpler than a bacterium, which itself is insanely complex? Why does all life share the same genetic and amino acid coding system, a relatively arbitrary choice? More likely, in all seriousness, that life originated in Mars and came here via panspermia during the early bombardment period. Mars was warm and wet while Earth was still suffering cataclysmic impacts and only relatively mature examples of Martian life (e.g. bacteria) would have survived the trip. If life originated multiple times on Earth there would be evidence for that. Heck if life originated on Earth there should be evidence for that, which there bizarrely isn’t.

fiblye 7y ago
The theory I’ve seen is that anything simpler couldn’t defend itself and would instantly be eaten by something more complex.
ajuc 7y ago
> Then why isn’t there ANY examples of life simpler than a bacterium, which itself is insanely complex? Exactly because they were outcompeted? If I understand correctly the early life would be living much slower and reproducing much less efficiently. So it would just get eaten by more efficient life that had millions years more to develop. How do you know life isn't arising every few million years somewhere on Earth and immediately being eaten by something before it could reproduce 10 times? What evidence would you expect to find that it happens?
- garmaine 7y ago
  Fossils. Micro or nano scale tracks of chemotropic entities. Unusual small geological features indicative of anything other than normal random chemistry going on. We can see all this in the rocks around us. TFA is about finding such things in mines deep underground. Remarkably we can even find such evidence in fossils more than 3 billion years old. Yet.. the oldest things we find are microbial sedentary structures indicative of remarkably complex life: with genes, ribosomes, proteins, etc. We know this because those same life forms still exist today and leave pretty much exactly the same tell tale signs. We call them simple life, but that is just by comparison. They are insanely complex compared to the random geochemistry going on alongside them. Why don’t we find ANYTHING older than this which differs from expected geological features? Where are the fossils from the origin of life? Also, the oldest fossils we have are of an organism that still exists: simple life remarkably doesn’t get competed to extinction. It turns out that simpler life forms have some advantages from their simplicity allowing them to be more adaptive to micro niches. So why don’t we have extant examples of even simpler life forms, surviving where complex life doesn’t fare as well?
  - andrewflnr 7y ago
    Possible answer: there was a hard takeoff in complexity between the first thing you can call life with a straight face and some minimal level of complexity you need to stay alive and spread in the real world. That minimal level of complexity characterizes the first organisms that show up in fossils. If it happened fast enough (maybe up to a couple million years, I dunno), there would be an infinitesimal amount of evidence that could easily be missed forever. If it only happened once, we would need to look at exactly the right rock, across the whole planet, with a microscope. Or it could already be recycled into the mantle. Ocean crust doesn't have a long lifespan, IIRC. Dunno about the rest, but I do think that rapid advancement from proto-life to something pretty sophisticated is likely, wherever it starts.
  - ajuc 7y ago
    Do we even know what we're looking for? Maybe some expected geologic features are the fossils of the first life? How do we know if the tell-tale signs produced by modern simple life couldn't be also produced by proto-life? Maybe they used some of the same processes without all the other stuff modern life does? Maybe life was bound to one location before it invented cells, and we just never checked that location? Maybe that location is now thousands meters below some ocean?
dpark 7y ago
> More likely, in all seriousness, that life originated in Mars and came here via panspermia during the early bombardment period. I am always surprised at the number of people willing to make assertions like this. Panspermia itself is a hypothesis. Panspermia from Mars specifically is a huge stretch. There is absolutely no basis for claiming that this is likely. > only relatively mature examples of Martian life (e.g. bacteria) would have survived the trip. Why do you make this assumption? Life complexity is not generally correlated with space survivability. At least not positively correlated.
- partialrecall 7y ago
  > "Panspermia itself is a hypothesis. Panspermia from Mars specifically is a huge stretch. There is absolutely no basis for claiming that this is likely." Perhaps not 'likely', but there is reason to believe it's plausible. Extremophile organisms plausibly capable of surviving in space for the requisite timespans are certainly known to exist, and there is also known to be small amounts of material transfer between earth and mars. The part I wonder about is whether any extremophile organism could survive the doubtlessly violent circumstances that are involved in ejecting rocks from either the earth or mars gravity well.
- garmaine 7y ago
  I’ve actually worked in astrobiology research :) I would point you towards the research that went into ALH-84001. Even if you don’t buy that it was an example of fossilized Martian life, analysis of the thermal stresses it suffered from ejection from Mars, time in flight, to impact on Earth showed conclusively that it was survivable. Had it been the other way around (Earth to Mars) it would have seeded Mars with life. We’ve shown that rock which could be carrying microbes can and has been exchanged between earth and Mars. Lots of such specimens land each and every year. You can quibble that we haven’t found actual life yet, but (1) lots of people think that’s exactly what ALH-84001 was. (2) we don’t have that many samples of Martian meteorites. We know lots of it falls every year, but most is either not found/collected/identified or contaminated on impact. (3) Mars meteorites falling now, ejected from a dry and sterile surface, would not be representative of what was falling in the early earth that was thrown from a wet, habitable Mars. To be clear, from an astrobiology perspective a negative result from the search for life on (or from) Mars is harder to explain than finding it. Both panspermia and second abiogenesis are simpler explanations.
chongli 7y ago
ANY examples of life simpler than a bacterium Viruses are much simpler, for one. Or perhaps you don't consider them to be life forms. Either way, if you understand how bacteria operate at even the most crude level, you'll realize that they (all bacteria, collectively; individually, they're specialized, of course) eat basically anything and everything in terms of organic molecules. What are the ramifications for this? It means any sort of abiogenesis that takes place today needs to somehow avoid being immediately eaten by bacteria and then continue to survive for potentially millions of years in order to evolve into an advanced life form. Needless to say, this seems to be vanishingly unlikely these days.
- garmaine 7y ago
  Viruses are life, but they depend on the machinery of other, more complex life to reproduce. Life doesn't start with viruses, for if it did, how would they reproduce?
  - chongli 7y ago
    You asked about examples of life simpler than bacteria. You didn't stipulate that they had to be ancestors. How would that even work, anyway? An organism would have to be extremely long-lived to be living concurrently with its direct, more complicated descendent.
    - TeMPOraL 7y ago
      > How would that even work, anyway? Think in terms of lines, not individuals. Mutations are acquired on individual level, so out of a whole family of bacteria, one individual may reproduce into something slightly different, while the rest of the family continue unchanged. (Modulo fast mutation rate in bacteria, and modulo the wide use of horizontal gene transfer. The more I learn about bacteria and archaea, the more I feel there's little point in trying to find the tree of life.)
- mirimir 7y ago
  As I vaguely understand it, both combination and separation have played important roles in evolution. Combination, for example, in that the nuclei, mitochondria and chloroplasts of modern eukaryotes derive from initially separate organisms. Many eukaryotes carry transposable elements, which are DNA sequences that exploit DNA and RNA machinery to create numerous copies of themselves in the genome. That is, they're like viruses, except that for the most part they don't get transmitted, except through cell replication. But I believe that there are examples where transposable elements do get transmitted like viruses. Or sometimes as parasites on actual viruses. So that's separation. And there are also examples, where viruses become integrated into the genome. Sometimes reversibly, as with HSV, which is why you can never really cure an HSV infection. Anyway, it seems most likely that simple stuff evolved first, and then combined into more complicated stuff. But the simple stuff has survived, to some extent, as transposable elements and viruses.
zaarn 7y ago
Mitochondria carry their own genome, which is substantially different to bacteria. Although nowadays a core part of eukaryotic cells, it's not hard to believe that they were once a separate form of life much simpler than a bacteria. Considering the age of life on this planet, panspermia from Mars is unlikely; in the early life of the solar system, the sun was much dimmer and Mars was significantly colder than today. Any liquid water on the surface, on which life as we know it could have developed, would only be present in fairly recent history (no longer than a billion years really).

fiblye 7y ago

The theory I’ve seen is that anything simpler couldn’t defend itself and would instantly be eaten by something more complex.

ajuc 7y ago

> Then why isn’t there ANY examples of life simpler than a bacterium, which itself is insanely complex? Exactly because they were outcompeted? If I understand correctly the early life would be living much slower and reproducing much less efficiently. So it would just get eaten by more efficient life that had millions years more to develop. How do you know life isn't arising every few million years somewhere on Earth and immediately being eaten by something before it could reproduce 10 times? What evidence would you expect to find that it happens?

garmaine 7y ago
Fossils. Micro or nano scale tracks of chemotropic entities. Unusual small geological features indicative of anything other than normal random chemistry going on. We can see all this in the rocks around us. TFA is about finding such things in mines deep underground. Remarkably we can even find such evidence in fossils more than 3 billion years old. Yet.. the oldest things we find are microbial sedentary structures indicative of remarkably complex life: with genes, ribosomes, proteins, etc. We know this because those same life forms still exist today and leave pretty much exactly the same tell tale signs. We call them simple life, but that is just by comparison. They are insanely complex compared to the random geochemistry going on alongside them. Why don’t we find ANYTHING older than this which differs from expected geological features? Where are the fossils from the origin of life? Also, the oldest fossils we have are of an organism that still exists: simple life remarkably doesn’t get competed to extinction. It turns out that simpler life forms have some advantages from their simplicity allowing them to be more adaptive to micro niches. So why don’t we have extant examples of even simpler life forms, surviving where complex life doesn’t fare as well?
- andrewflnr 7y ago
  Possible answer: there was a hard takeoff in complexity between the first thing you can call life with a straight face and some minimal level of complexity you need to stay alive and spread in the real world. That minimal level of complexity characterizes the first organisms that show up in fossils. If it happened fast enough (maybe up to a couple million years, I dunno), there would be an infinitesimal amount of evidence that could easily be missed forever. If it only happened once, we would need to look at exactly the right rock, across the whole planet, with a microscope. Or it could already be recycled into the mantle. Ocean crust doesn't have a long lifespan, IIRC. Dunno about the rest, but I do think that rapid advancement from proto-life to something pretty sophisticated is likely, wherever it starts.
- ajuc 7y ago
  Do we even know what we're looking for? Maybe some expected geologic features are the fossils of the first life? How do we know if the tell-tale signs produced by modern simple life couldn't be also produced by proto-life? Maybe they used some of the same processes without all the other stuff modern life does? Maybe life was bound to one location before it invented cells, and we just never checked that location? Maybe that location is now thousands meters below some ocean?

dpark 7y ago

> More likely, in all seriousness, that life originated in Mars and came here via panspermia during the early bombardment period. I am always surprised at the number of people willing to make assertions like this. Panspermia itself is a hypothesis. Panspermia from Mars specifically is a huge stretch. There is absolutely no basis for claiming that this is likely. > only relatively mature examples of Martian life (e.g. bacteria) would have survived the trip. Why do you make this assumption? Life complexity is not generally correlated with space survivability. At least not positively correlated.

partialrecall 7y ago
> "Panspermia itself is a hypothesis. Panspermia from Mars specifically is a huge stretch. There is absolutely no basis for claiming that this is likely." Perhaps not 'likely', but there is reason to believe it's plausible. Extremophile organisms plausibly capable of surviving in space for the requisite timespans are certainly known to exist, and there is also known to be small amounts of material transfer between earth and mars. The part I wonder about is whether any extremophile organism could survive the doubtlessly violent circumstances that are involved in ejecting rocks from either the earth or mars gravity well.
garmaine 7y ago
I’ve actually worked in astrobiology research :) I would point you towards the research that went into ALH-84001. Even if you don’t buy that it was an example of fossilized Martian life, analysis of the thermal stresses it suffered from ejection from Mars, time in flight, to impact on Earth showed conclusively that it was survivable. Had it been the other way around (Earth to Mars) it would have seeded Mars with life. We’ve shown that rock which could be carrying microbes can and has been exchanged between earth and Mars. Lots of such specimens land each and every year. You can quibble that we haven’t found actual life yet, but (1) lots of people think that’s exactly what ALH-84001 was. (2) we don’t have that many samples of Martian meteorites. We know lots of it falls every year, but most is either not found/collected/identified or contaminated on impact. (3) Mars meteorites falling now, ejected from a dry and sterile surface, would not be representative of what was falling in the early earth that was thrown from a wet, habitable Mars. To be clear, from an astrobiology perspective a negative result from the search for life on (or from) Mars is harder to explain than finding it. Both panspermia and second abiogenesis are simpler explanations.

chongli 7y ago

ANY examples of life simpler than a bacterium Viruses are much simpler, for one. Or perhaps you don't consider them to be life forms. Either way, if you understand how bacteria operate at even the most crude level, you'll realize that they (all bacteria, collectively; individually, they're specialized, of course) eat basically anything and everything in terms of organic molecules. What are the ramifications for this? It means any sort of abiogenesis that takes place today needs to somehow avoid being immediately eaten by bacteria and then continue to survive for potentially millions of years in order to evolve into an advanced life form. Needless to say, this seems to be vanishingly unlikely these days.

garmaine 7y ago
Viruses are life, but they depend on the machinery of other, more complex life to reproduce. Life doesn't start with viruses, for if it did, how would they reproduce?
- chongli 7y ago
  You asked about examples of life simpler than bacteria. You didn't stipulate that they had to be ancestors. How would that even work, anyway? An organism would have to be extremely long-lived to be living concurrently with its direct, more complicated descendent.
  - TeMPOraL 7y ago
    > How would that even work, anyway? Think in terms of lines, not individuals. Mutations are acquired on individual level, so out of a whole family of bacteria, one individual may reproduce into something slightly different, while the rest of the family continue unchanged. (Modulo fast mutation rate in bacteria, and modulo the wide use of horizontal gene transfer. The more I learn about bacteria and archaea, the more I feel there's little point in trying to find the tree of life.)
mirimir 7y ago
As I vaguely understand it, both combination and separation have played important roles in evolution. Combination, for example, in that the nuclei, mitochondria and chloroplasts of modern eukaryotes derive from initially separate organisms. Many eukaryotes carry transposable elements, which are DNA sequences that exploit DNA and RNA machinery to create numerous copies of themselves in the genome. That is, they're like viruses, except that for the most part they don't get transmitted, except through cell replication. But I believe that there are examples where transposable elements do get transmitted like viruses. Or sometimes as parasites on actual viruses. So that's separation. And there are also examples, where viruses become integrated into the genome. Sometimes reversibly, as with HSV, which is why you can never really cure an HSV infection. Anyway, it seems most likely that simple stuff evolved first, and then combined into more complicated stuff. But the simple stuff has survived, to some extent, as transposable elements and viruses.

zaarn 7y ago

Mitochondria carry their own genome, which is substantially different to bacteria. Although nowadays a core part of eukaryotic cells, it's not hard to believe that they were once a separate form of life much simpler than a bacteria. Considering the age of life on this planet, panspermia from Mars is unlikely; in the early life of the solar system, the sun was much dimmer and Mars was significantly colder than today. Any liquid water on the surface, on which life as we know it could have developed, would only be present in fairly recent history (no longer than a billion years really).