3 ms·

I'm more partial to the idea that RNA based life developed outside earth. (panspermia theory)

by singularity2001 6y ago

jonathanlydall 6y ago
I don’t dispute the possibility, but it does beg the question of why that’s more likely than life developing on Earth?
- skohan 6y ago
  In a lot of ways it's just punting the problem isn't it?
  - hcarvalhoalves 6y ago
    I think Panspermia could explain why it's so hard to reproduce the first organisms in a lab by mimicking Earth's early conditions - we could be using the wrong conditions altogether. E.g. we could be ignoring the effect of solar radiation from another atmosphere, or very high/low atmospheric pressure, etc.
    - skohan 6y ago
      I mean it could also have taken a really long time, right? like the correct conditions could have existed for tens of thousands of years or more before the chance collisions occurred which resulted in self-replicating life.
- jcims 6y ago
  I'm of the same notion, just because the basic combinatorics of various features of even the simplest self-replicating life forms are so exceedingly unlikely that to me the idea that they were developed stochastically in relatively rapid succession in the first billion years on earth just doesn't add up. It will become clear that I'm no expert, but this has fascinated me a bit and I've seen a few articles about simplest self-replicators. In a lab they've constructed enzymes [1] that are able to do some replication with as few as 160-190 bases of RNA, but they aren't self-replicating, they spew out some subset of themselves. RNA is just half of DNA with each base in a particular sequence being one of four possible nucleotides (A, C, G and U). In the smallest case above, you have 160 nucleotides giving the entire string of RNA a molar mass of ~ ~50kDa [2] (approximately 50kg per mole of that RNA string). There are ~4^160 combinations of just this extremely short and as far as we know insufficient string of RNA to build even the simplest self-replicator. 4^160 is approximately 2e96 combinations. If you wanted to try every one of those combinations, you would be assembling (2e96 / 6e23) approximately 3e72 moles of RNA. To do it in one shot you would need more mass than in the observable universe (closer to a billion universes). To do it with just the mass of the earth (forget surface/hydrocarbons/biomass) in four billion years you'd have to recycle at relativistic speeds. Obviously it happened, and the above 'needle in a haystack' assessment has many problems as well. But the numbers are so big that no matter how you slice it I can see a scenario where it plausibly only happened once in the history of the universe. Either that or the stochastic parts of the explanation of abiogenesis are incomplete. 1 - https://doi.org/10.1126/science.1200752 https://doi.org/10.1126/science.1200752 2 - https://bionumbers.hms.harvard.edu/files/Nucleic%20Acids_Sizes_and_Molecular_Weights_2pgs.pdf https://bionumbers.hms.harvard.edu/files/Nucleic%20Acids_Siz...
- mr_toad 6y ago
  > why that’s more likely than life developing on Earth? Possibly because the Universe is much older than our planet, and life could have been evolving out there for billions of years before Earth even existed.
fsloth 6y ago
The RNA had still to originally come from somewhere. Big bang produced hydrogen and helium. Primordial stars converted those to heavier elements - carbon, nitrogen... and at some point in time between the first stars exploding and spreading the heavier elements into the universe, and now, the first RNA molecules were formed. What was the chemical process that produced them is the specific question here. Not where in universe this happened. Although that question is exciting as well. Nothing stops from using Darwin's idea here as well - there was a puddle on a planet, somehwere else, long ago and far away... Panspermia makes the argument actually more complex, not simpler. But it's not unlikely - space is apparently full of rocks from far away places.

I'm more partial to the idea that RNA based life developed outside earth. (panspermia theory)

jonathanlydall 6y ago

I don’t dispute the possibility, but it does beg the question of why that’s more likely than life developing on Earth?

skohan 6y ago
In a lot of ways it's just punting the problem isn't it?
- hcarvalhoalves 6y ago
  I think Panspermia could explain why it's so hard to reproduce the first organisms in a lab by mimicking Earth's early conditions - we could be using the wrong conditions altogether. E.g. we could be ignoring the effect of solar radiation from another atmosphere, or very high/low atmospheric pressure, etc.
  - skohan 6y ago
    I mean it could also have taken a really long time, right? like the correct conditions could have existed for tens of thousands of years or more before the chance collisions occurred which resulted in self-replicating life.
jcims 6y ago
I'm of the same notion, just because the basic combinatorics of various features of even the simplest self-replicating life forms are so exceedingly unlikely that to me the idea that they were developed stochastically in relatively rapid succession in the first billion years on earth just doesn't add up. It will become clear that I'm no expert, but this has fascinated me a bit and I've seen a few articles about simplest self-replicators. In a lab they've constructed enzymes [1] that are able to do some replication with as few as 160-190 bases of RNA, but they aren't self-replicating, they spew out some subset of themselves. RNA is just half of DNA with each base in a particular sequence being one of four possible nucleotides (A, C, G and U). In the smallest case above, you have 160 nucleotides giving the entire string of RNA a molar mass of ~ ~50kDa [2] (approximately 50kg per mole of that RNA string). There are ~4^160 combinations of just this extremely short and as far as we know insufficient string of RNA to build even the simplest self-replicator. 4^160 is approximately 2e96 combinations. If you wanted to try every one of those combinations, you would be assembling (2e96 / 6e23) approximately 3e72 moles of RNA. To do it in one shot you would need more mass than in the observable universe (closer to a billion universes). To do it with just the mass of the earth (forget surface/hydrocarbons/biomass) in four billion years you'd have to recycle at relativistic speeds. Obviously it happened, and the above 'needle in a haystack' assessment has many problems as well. But the numbers are so big that no matter how you slice it I can see a scenario where it plausibly only happened once in the history of the universe. Either that or the stochastic parts of the explanation of abiogenesis are incomplete. 1 - https://doi.org/10.1126/science.1200752 https://doi.org/10.1126/science.1200752 2 - https://bionumbers.hms.harvard.edu/files/Nucleic%20Acids_Sizes_and_Molecular_Weights_2pgs.pdf https://bionumbers.hms.harvard.edu/files/Nucleic%20Acids_Siz...
mr_toad 6y ago
> why that’s more likely than life developing on Earth? Possibly because the Universe is much older than our planet, and life could have been evolving out there for billions of years before Earth even existed.

fsloth 6y ago

The RNA had still to originally come from somewhere. Big bang produced hydrogen and helium. Primordial stars converted those to heavier elements - carbon, nitrogen... and at some point in time between the first stars exploding and spreading the heavier elements into the universe, and now, the first RNA molecules were formed. What was the chemical process that produced them is the specific question here. Not where in universe this happened. Although that question is exciting as well. Nothing stops from using Darwin's idea here as well - there was a puddle on a planet, somehwere else, long ago and far away... Panspermia makes the argument actually more complex, not simpler. But it's not unlikely - space is apparently full of rocks from far away places.