2 ms·

Would love to see some sources for #1. #2 sounds plausible but speculative?

by bavell 11mo ago

smallmancontrov 11mo ago
RNA World is really cooking: https://pubmed.ncbi.nlm.nih.gov/39358873/ https://pubmed.ncbi.nlm.nih.gov/39358873/ Ejection: https://link.springer.com/chapter/10.1007/3-540-25736-5_3 https://link.springer.com/chapter/10.1007/3-540-25736-5_3 Reentry: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0132611 https://journals.plos.org/plosone/article?id=10.1371/journal... Not to mention the constant trickle of "X survived in space" stories that we get every time someone bothers to collect and culture a sample. The amount of success at every stage with, frankly, very little effort spent tuning the conditions, multiplied by "bacteria are everywhere" makes hitchhiking less crazy than it sounds. Our intuition misleads us because bacteria are so much better at handling acceleration (easy if you're small) and dessiccation (everywhere is a desert if you're small) than anything we are used to thinking about.
- Egret 11mo ago
  https://pmc.ncbi.nlm.nih.gov/articles/PMC1892545/ https://pmc.ncbi.nlm.nih.gov/articles/PMC1892545/ An upper bound probability for the RNA world hypothesis is 10^-1018. A reasonable interpretation is that the RNA world hypothesis is impossible in the real world.
  - avadodin 11mo ago
    A superficial reading doesn't inspire much confidence in this peer-reviewed article but I agree that RNA-world is a thought experiment at best. There is no evidence of these RNA structures in actual lifeforms. RNA encodes proteins. The most parsimonious explanation is that proteins(likely incapable of true replication by themselves) preceded RNA even if an RNA-based system can be designed in theory. I won't make claims of probability of unknown processes but proteins exist that can assemble spare nucleotides and proteins exist that can assemble proteins out of nucleotide chains. All you need is a pair of them to come in the vicinity of each other and wait until RNA comes along that encodes a similar-enough pair.
    - Egret 11mo ago
      The probability of assembling two proteins randomly close by in spatial and temporal terms runs into Chadwick's proximity problem.
9dev 11mo ago
Panspermia is pretty much irrelevant to the actual question though; even assuming life got to Earth the hitchhiker way, it would have to have developed on another planet, and we’re back to square one.
- actionfromafar 11mo ago
  Panspermia is kind of weird to think about IMHO. Because, it likely took a long time to develop and a long time to travel here. So it must have started a long time ago. Before the Solar system was created. But Sol is pretty old. How early could life have started really?
  - jiggawatts 11mo ago
    The earliest galaxies formed when the universe was just a few hundred million years old, which means there may have been planets that are 3x times older than Earth. Several caveats apply, chiefly that heavy elements weren't produced for a while in significant quantity, but were produced fairly early on due to large stars exploding relatively quickly, when they were merely tens of millions of years old, if that.
  - lioeters 11mo ago
    That gets into astrobiology. Theoretically life could have started as soon as its basic ingredients were ready. So not until things had cooled down a bit after the Bang, when there were heavier elements than hydrogen and helium; and some kind of land and water. > In the redshift range 100 . (1 + z) . 137, the cosmic microwave background (CMB) had a temperature of 273–373 K (0-100◦C), allowing early rocky planets (if any existed) to have liquid water chemistry on their surface and be habitable, irrespective of their distance from a star. > In the standard ΛCDM cosmology, the first star-forming halos within our Hubble volume started collapsing at these redshifts,allowing the chemistry of life to possibly begin when the Universe was merely 10–17 million years old. From: The Habitable Epoch of the Early Universe - https://arxiv.org/abs/1312.0613 https://arxiv.org/abs/1312.0613 In comparison, our beloved sun is estimated to have been born 9.2 billion years after the Big Bang, a third of the way into the universe's history so far. > The Sun is approximately 4.6 billion years old, while the age of the universe, based on current estimates, is about 13.8 billion years. So our solar system is not that old, relatively speaking. We're among elders, some stars are three times older than the sun. > In the future, however, life might continue to emerge on planets orbiting dwarf stars, like our nearest neighbor, Proxima Centauri, which will endure hundreds of times longer than the sun’s. > Ultimately, it would be desirable for humanity to relocate to a habitable planet around a dwarf star like Proxima Centauri b, where it could keep itself warm near a natural nuclear furnace for up to 10 trillion years into the future.

Would love to see some sources for #1. #2 sounds plausible but speculative?

by bavell 11mo ago

Would love to see some sources for #1. #2 sounds plausible but speculative?

RNA World is really cooking: https://pubmed.ncbi.nlm.nih.gov/39358873/ https://pubmed.ncbi.nlm.nih.gov/39358873/ Ejection: https://link.springer.com/chapter/10.1007/3-540-25736-5_3 https://link.springer.com/chapter/10.1007/3-540-25736-5_3 Reentry: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0132611 https://journals.plos.org/plosone/article?id=10.1371/journal... Not to mention the constant trickle of "X survived in space" stories that we get every time someone bothers to collect and culture a sample. The amount of success at every stage with, frankly, very little effort spent tuning the conditions, multiplied by "bacteria are everywhere" makes hitchhiking less crazy than it sounds. Our intuition misleads us because bacteria are so much better at handling acceleration (easy if you're small) and dessiccation (everywhere is a desert if you're small) than anything we are used to thinking about.

Egret 11mo ago
https://pmc.ncbi.nlm.nih.gov/articles/PMC1892545/ https://pmc.ncbi.nlm.nih.gov/articles/PMC1892545/ An upper bound probability for the RNA world hypothesis is 10^-1018. A reasonable interpretation is that the RNA world hypothesis is impossible in the real world.
- avadodin 11mo ago
  A superficial reading doesn't inspire much confidence in this peer-reviewed article but I agree that RNA-world is a thought experiment at best. There is no evidence of these RNA structures in actual lifeforms. RNA encodes proteins. The most parsimonious explanation is that proteins(likely incapable of true replication by themselves) preceded RNA even if an RNA-based system can be designed in theory. I won't make claims of probability of unknown processes but proteins exist that can assemble spare nucleotides and proteins exist that can assemble proteins out of nucleotide chains. All you need is a pair of them to come in the vicinity of each other and wait until RNA comes along that encodes a similar-enough pair.
  - Egret 11mo ago
    The probability of assembling two proteins randomly close by in spatial and temporal terms runs into Chadwick's proximity problem.

9dev 11mo ago

Panspermia is pretty much irrelevant to the actual question though; even assuming life got to Earth the hitchhiker way, it would have to have developed on another planet, and we’re back to square one.

actionfromafar 11mo ago
Panspermia is kind of weird to think about IMHO. Because, it likely took a long time to develop and a long time to travel here. So it must have started a long time ago. Before the Solar system was created. But Sol is pretty old. How early could life have started really?
- jiggawatts 11mo ago
  The earliest galaxies formed when the universe was just a few hundred million years old, which means there may have been planets that are 3x times older than Earth. Several caveats apply, chiefly that heavy elements weren't produced for a while in significant quantity, but were produced fairly early on due to large stars exploding relatively quickly, when they were merely tens of millions of years old, if that.
- lioeters 11mo ago
  That gets into astrobiology. Theoretically life could have started as soon as its basic ingredients were ready. So not until things had cooled down a bit after the Bang, when there were heavier elements than hydrogen and helium; and some kind of land and water. > In the redshift range 100 . (1 + z) . 137, the cosmic microwave background (CMB) had a temperature of 273–373 K (0-100◦C), allowing early rocky planets (if any existed) to have liquid water chemistry on their surface and be habitable, irrespective of their distance from a star. > In the standard ΛCDM cosmology, the first star-forming halos within our Hubble volume started collapsing at these redshifts,allowing the chemistry of life to possibly begin when the Universe was merely 10–17 million years old. From: The Habitable Epoch of the Early Universe - https://arxiv.org/abs/1312.0613 https://arxiv.org/abs/1312.0613 In comparison, our beloved sun is estimated to have been born 9.2 billion years after the Big Bang, a third of the way into the universe's history so far. > The Sun is approximately 4.6 billion years old, while the age of the universe, based on current estimates, is about 13.8 billion years. So our solar system is not that old, relatively speaking. We're among elders, some stars are three times older than the sun. > In the future, however, life might continue to emerge on planets orbiting dwarf stars, like our nearest neighbor, Proxima Centauri, which will endure hundreds of times longer than the sun’s. > Ultimately, it would be desirable for humanity to relocate to a habitable planet around a dwarf star like Proxima Centauri b, where it could keep itself warm near a natural nuclear furnace for up to 10 trillion years into the future.