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Id bet that having two other planets that were habitable in the early system is why the Earth developed complex life. These planets aren’t closed systems but i

Id bet that having two other planets that were habitable in the early system is why the Earth developed complex life. These planets aren’t closed systems but instead they constantly (in astronomical terms) flung matter back and forth.

adastra22 4y ago
There's a very, very good chance that we are actually Martian life. There is absolutely no evidence whatsoever anywhere on earth for life less complex than eukaryotic cells. LUCA, the last-universal-common-ancestor of all life on Earth, is hypothesized to have been fiendishly complex with some 350 genes. Part of the difficulty of studying abiogenesis is that there is literally no evidence for or remnants of any simpler / earlier kind of life anywhere on Earth. Evidence of this kind of microbial life appears out of the blue not long after the Earth cools from the Moon-forming Thea impact. These specific genes are evidence that LUCA was a rock-boring microbe of exactly the sort that would have survived a Mars-Earth transfer event like ALH-84001. And Mars, during this time, had been warm and wet for a hundred million years or so longer than the Earth. I would bet money that we're dependents of Martian microbes.
- mtlmtlmtlmtl 4y ago
  I'm very sceptical of this. It's a distinct possibility, and it's even pretty likely, but I don't think Earth based abiogenesis is even close to being seen as unlikely. It's still the simpler explanation in my opinion. The lack of fossils is not too convincing since microbes don't fossilise well. And it's entirely possible that life from the RNA world was just outcompeted by prokaryotic, DNA-based life. There's also the question of RNA viruses and viroids, which could be descendants of the RNA world.
  - mjan22640 4y ago
    Parasites in general undergo simplification, they reduce and eventually lose the functionality that the host provides for them. In my opinion this is the case in viruses, that they are so simple not because they are remnants of ancient life, but because that they are parasites that underwent secondary simplification.
    - mtlmtlmtlmtl 4y ago
      That's one of the 3 most popular hypotheses, mine is another. But the jury is still very much out on this one.
  - adastra22 4y ago
    Microbial life doesn't fossilize well, but the earliest secondary fossils we do have are of microbial mats. They exactly match in all respects certain microbial mat living fossils we see on the ocean today, produced by relatively complex life forms. Most hypothecated pathways for abiogenesis would have left similar secondary fossils in the geologic record. Yet we don't see them. There's not a lot of rock left from that long ago, so maybe it just didn't get preserved. But it is striking and unexpected how (1) the earliest fossils are of quite complex organisms; (2) they pop into existence very soon after the Earth cools; yet (3) they don't evolve into any more complex patterns until hundreds of millions of years later. So life evolved quickly (10's of millions of years), rapidly developed complex features, then whatever evolutionary force drove that suddenly stopped and they stayed stable and unchanged for half a billion years? It is actually a simpler supposition that life evolved on Mars (or Venus, but panspermia from Mars is more likely), and a relatively complex LUCA was transferred to newly reformed Earth via an impact event. This explains all of the oddities around LUCA and the fossil record of the origin of life on Earth. Mars would have had a vibrant early-life ecosystem that provided an evolutionary push for complexity. LUCA, on the other hand, colonized a lifeless Eden and was able to spend 100's of millions of years without evolutionary pressures. And as the science surrounding ALH-84001 shows, panspermia is not an unlikely event at all. If there was life on Mars at all, it absolutely would have been transferred.
    - mtlmtlmtlmtl 4y ago
      >Microbial life fossils But since the RNA world is still poorly understood, and the nature of the lifeforms is highly speculative, there are many possible explanations for this consistent with an Earth origin. For instance it could be that RNA life didn't form microbial mats, or was geographically much more limited(perhaps only existing in deep sea vents, much more dependant on chemistry from the environment) until colonising the rest of the ocean later, leading to a much stronger signal in the fossil record. The RNA world might have been much shorter lived too for reason I'll get back to. >popping into existence and only complexifying after hundreds of My One very plausible explanation for this apparent lag is that the evolution of eukaryotes was a very unlikely event like endosymbiosis. Couple with the fact that RNA based life would be much more genetically unstable, allowing to evolve faster, and might have been much more fragile, representing a stronger selective pressure. Whereas DNA based prokaryotes are extremely versatile, which is clear from the fact that they've colonised the entire planet and lived through more drastic changes in climate than any other life form on earth. There's also no reason that I know of to think Mars was a more(or less) likely location for abiogenesis to have occured than Earth was. More and more evidence is suggesting that the building blocks for RNA are quite abundant even sans planets, and that abiogenesis itself might actually be very likely, but later complexification might not be. I think both hypotheses have a lot of merit. Although I will say if we find life on Mars and it turns out we are Martians I will be disappointed, because it would mean we still only have one sample of life. There's also a possibility that there was life on mars seeded from Earth, some of which came back to us fossilised, though I'm still undecided on whether ALH-84001 contains any fossils or not. There doesn't seem to be much consensus there.
- mjan22640 4y ago
  Life might be older than Solar system https://www.overcomingbias.com/2015/03/life-before-earth.html https://www.overcomingbias.com/2015/03/life-before-earth.htm... The core life elements (H), C, O, N were produced by the first generation of stars. A rocky planet surface is almost all just silica on the other hand.
  - adastra22 4y ago
    I don't think that post is very interesting from an origin of life perspective. The factors which limit genome growth would not have been in play at the origin of life. If the RNA origin theory of life is correct, then our oldest ancestors were replicating pieces of RNA in some sort of primordial soup. In that environment there would have been pieces of RNA everywhere whizzing about, combing, recombining, and replicating. There would have been explosive growth in "genome" size in very short amount of time, because changes would be spontaneously happening without the need for slow cycles of mutation and natural selection, which would come to dominate later.
- Mistletoe 4y ago
  What is special about Mars that makes it likely life formed there first instead of here? Just the 100 million year warm and wet headstart?
  - adastra22 4y ago
    Mars is smaller so it cooled faster after formation. Also with its thicker early atmosphere it probably was at just the right distance from the sun to be what we would consider an ideal temperature, even accounting for the dimmer sun at the time. Finally, Earth was shattered by the Moon-forming collision with Thea, which basically reset the cooldown clock for our planet. All these factors together mean that Mars had a heck of a head start.
    - Mistletoe 4y ago
      Really interesting, thanks!
      - adastra22 4y ago
        No problem!
- ProjectArcturis 4y ago
  >There is absolutely no evidence whatsoever anywhere on earth for life less complex than eukaryotic cells. I'm not sure what you meant to say here, but this is absolutely false. Prokaryotes abound.
  - adastra22 4y ago
    I brain farted. Obviously I meant prokaryotic cells, as the later context makes clear. Edit window has elapsed. Thanks for the correction.
- andrewflnr 4y ago
  Do you have a good link about LUCA genes looking like a rock-boring microbe? That still sounds vaguely consistent with earth-based abiogenesis, but interesting for sure.
  - adastra22 4y ago
    I’m having trouble finding an article to back up my claim, so I fear I must be misremembering. Current consensus seems to be that LUCA was part of the hydrothermal vent ecosystem.
    - andrewflnr 4y ago
      Right, I'm not a microbiologist, but it seemed like similar genes might be involved for chemoautotrophy(?) that we would expect in early earth-based life at a vent system as for rock-boring microbes that could survive a trip from Mars to Earth. I appreciate you replying, though. :)
      - adastra22 4y ago
        That's my understanding as well. But I'm also not an astrobiologist. Just spent a couple of years working with them.

adastra22 4y ago

There's a very, very good chance that we are actually Martian life. There is absolutely no evidence whatsoever anywhere on earth for life less complex than eukaryotic cells. LUCA, the last-universal-common-ancestor of all life on Earth, is hypothesized to have been fiendishly complex with some 350 genes. Part of the difficulty of studying abiogenesis is that there is literally no evidence for or remnants of any simpler / earlier kind of life anywhere on Earth. Evidence of this kind of microbial life appears out of the blue not long after the Earth cools from the Moon-forming Thea impact. These specific genes are evidence that LUCA was a rock-boring microbe of exactly the sort that would have survived a Mars-Earth transfer event like ALH-84001. And Mars, during this time, had been warm and wet for a hundred million years or so longer than the Earth. I would bet money that we're dependents of Martian microbes.

mtlmtlmtlmtl 4y ago
I'm very sceptical of this. It's a distinct possibility, and it's even pretty likely, but I don't think Earth based abiogenesis is even close to being seen as unlikely. It's still the simpler explanation in my opinion. The lack of fossils is not too convincing since microbes don't fossilise well. And it's entirely possible that life from the RNA world was just outcompeted by prokaryotic, DNA-based life. There's also the question of RNA viruses and viroids, which could be descendants of the RNA world.
- mjan22640 4y ago
  Parasites in general undergo simplification, they reduce and eventually lose the functionality that the host provides for them. In my opinion this is the case in viruses, that they are so simple not because they are remnants of ancient life, but because that they are parasites that underwent secondary simplification.
  - mtlmtlmtlmtl 4y ago
    That's one of the 3 most popular hypotheses, mine is another. But the jury is still very much out on this one.
- adastra22 4y ago
  Microbial life doesn't fossilize well, but the earliest secondary fossils we do have are of microbial mats. They exactly match in all respects certain microbial mat living fossils we see on the ocean today, produced by relatively complex life forms. Most hypothecated pathways for abiogenesis would have left similar secondary fossils in the geologic record. Yet we don't see them. There's not a lot of rock left from that long ago, so maybe it just didn't get preserved. But it is striking and unexpected how (1) the earliest fossils are of quite complex organisms; (2) they pop into existence very soon after the Earth cools; yet (3) they don't evolve into any more complex patterns until hundreds of millions of years later. So life evolved quickly (10's of millions of years), rapidly developed complex features, then whatever evolutionary force drove that suddenly stopped and they stayed stable and unchanged for half a billion years? It is actually a simpler supposition that life evolved on Mars (or Venus, but panspermia from Mars is more likely), and a relatively complex LUCA was transferred to newly reformed Earth via an impact event. This explains all of the oddities around LUCA and the fossil record of the origin of life on Earth. Mars would have had a vibrant early-life ecosystem that provided an evolutionary push for complexity. LUCA, on the other hand, colonized a lifeless Eden and was able to spend 100's of millions of years without evolutionary pressures. And as the science surrounding ALH-84001 shows, panspermia is not an unlikely event at all. If there was life on Mars at all, it absolutely would have been transferred.
  - mtlmtlmtlmtl 4y ago
    >Microbial life fossils But since the RNA world is still poorly understood, and the nature of the lifeforms is highly speculative, there are many possible explanations for this consistent with an Earth origin. For instance it could be that RNA life didn't form microbial mats, or was geographically much more limited(perhaps only existing in deep sea vents, much more dependant on chemistry from the environment) until colonising the rest of the ocean later, leading to a much stronger signal in the fossil record. The RNA world might have been much shorter lived too for reason I'll get back to. >popping into existence and only complexifying after hundreds of My One very plausible explanation for this apparent lag is that the evolution of eukaryotes was a very unlikely event like endosymbiosis. Couple with the fact that RNA based life would be much more genetically unstable, allowing to evolve faster, and might have been much more fragile, representing a stronger selective pressure. Whereas DNA based prokaryotes are extremely versatile, which is clear from the fact that they've colonised the entire planet and lived through more drastic changes in climate than any other life form on earth. There's also no reason that I know of to think Mars was a more(or less) likely location for abiogenesis to have occured than Earth was. More and more evidence is suggesting that the building blocks for RNA are quite abundant even sans planets, and that abiogenesis itself might actually be very likely, but later complexification might not be. I think both hypotheses have a lot of merit. Although I will say if we find life on Mars and it turns out we are Martians I will be disappointed, because it would mean we still only have one sample of life. There's also a possibility that there was life on mars seeded from Earth, some of which came back to us fossilised, though I'm still undecided on whether ALH-84001 contains any fossils or not. There doesn't seem to be much consensus there.
mjan22640 4y ago
Life might be older than Solar system https://www.overcomingbias.com/2015/03/life-before-earth.html https://www.overcomingbias.com/2015/03/life-before-earth.htm... The core life elements (H), C, O, N were produced by the first generation of stars. A rocky planet surface is almost all just silica on the other hand.
- adastra22 4y ago
  I don't think that post is very interesting from an origin of life perspective. The factors which limit genome growth would not have been in play at the origin of life. If the RNA origin theory of life is correct, then our oldest ancestors were replicating pieces of RNA in some sort of primordial soup. In that environment there would have been pieces of RNA everywhere whizzing about, combing, recombining, and replicating. There would have been explosive growth in "genome" size in very short amount of time, because changes would be spontaneously happening without the need for slow cycles of mutation and natural selection, which would come to dominate later.
Mistletoe 4y ago
What is special about Mars that makes it likely life formed there first instead of here? Just the 100 million year warm and wet headstart?
- adastra22 4y ago
  Mars is smaller so it cooled faster after formation. Also with its thicker early atmosphere it probably was at just the right distance from the sun to be what we would consider an ideal temperature, even accounting for the dimmer sun at the time. Finally, Earth was shattered by the Moon-forming collision with Thea, which basically reset the cooldown clock for our planet. All these factors together mean that Mars had a heck of a head start.
  - Mistletoe 4y ago
    Really interesting, thanks!
    - adastra22 4y ago
      No problem!
ProjectArcturis 4y ago
>There is absolutely no evidence whatsoever anywhere on earth for life less complex than eukaryotic cells. I'm not sure what you meant to say here, but this is absolutely false. Prokaryotes abound.
- adastra22 4y ago
  I brain farted. Obviously I meant prokaryotic cells, as the later context makes clear. Edit window has elapsed. Thanks for the correction.
andrewflnr 4y ago
Do you have a good link about LUCA genes looking like a rock-boring microbe? That still sounds vaguely consistent with earth-based abiogenesis, but interesting for sure.
- adastra22 4y ago
  I’m having trouble finding an article to back up my claim, so I fear I must be misremembering. Current consensus seems to be that LUCA was part of the hydrothermal vent ecosystem.
  - andrewflnr 4y ago
    Right, I'm not a microbiologist, but it seemed like similar genes might be involved for chemoautotrophy(?) that we would expect in early earth-based life at a vent system as for rock-boring microbes that could survive a trip from Mars to Earth. I appreciate you replying, though. :)
    - adastra22 4y ago
      That's my understanding as well. But I'm also not an astrobiologist. Just spent a couple of years working with them.