5 ms·

It's interesting, that we're getting down to the sizes of self-replicating RNA that realistically can form by a complete accident. Getting this sequence by ran

by cyberax 8mo ago

It's interesting, that we're getting down to the sizes of self-replicating RNA that realistically can form by a complete accident. Getting this sequence by random chance out of a pile of nucleotides is a 1 in 2^90 chance. That's around 1.2*10^27 or just around 20000 moles! Not at all an impossible number.

jjk166 8mo ago
Note that the Bennu asteroid sample had approximately 5 nanomoles of nucleotides per gram, meaning 20,000 moles of nucleotides could be delivered by a single 4 million ton asteroid, which if it were a spherical carbonaceous chondrite would be about 183 meters in diameter. An asteroid about that size impacts earth roughly every 36,000 years, and that mass of meteor material falls to earth each century. If primordial earth's oceans had nucleotide concentrations comparable to Bennu, then there would be about 10^39 nucleotides in the ocean.
- nkrisc 8mo ago
  If raw materials isn’t the bottle neck for life every where, then what might it further down the line between oceans full of nucleotides and life? The oceans themselves?
  - cousinbryce 8mo ago
    Temperature range and magnetic field are my first thoughts.
- dekhn 8mo ago
  I don't see any reason for the source molecules to come from space. We already know that nucleotides will spontaneously form and polymerize in conditions consistent with the early earth, and a meteorite origin just moves the source of those nucleotides elsewhere but doesn't answer how they formed.
  - rolph 8mo ago
    space has been around for a lot longer than earth, its possible that inter planetary generation of nucleic acids may be primarily a matter of chemistry. Nucleobase synthesis in interstellar ices[2019] https://www.nature.com/articles/s41467-019-12404-1?error=server_error#Abs1 https://www.nature.com/articles/s41467-019-12404-1?error=ser... Chemistry of Abiotic Nucleotide Synthesis[2020] https://pubs.acs.org/doi/10.1021/acs.chemrev.9b00546 https://pubs.acs.org/doi/10.1021/acs.chemrev.9b00546
  - heavyset_go 8mo ago
    It's possible (proto-)life evolved in the pre-Earth protoplanetary disk. If so, life might not require a special snowflake planet like Earth to develop. Development could be solar system-wide, and common in other early solar systems.
  - jjk166 8mo ago
    Delivery by meteorites isn't necessarily the only or even primary source, but the fact is that it is a source we can directly observe, and it is a sufficient source. Earth's primordial chemistry likely did create more, but the existence of those conditions is theoretical, and such additional production need not be invoked to explain the needed level of abundance. Even a world with very different conditions from primordial Earth would likewise receive vast quantities of nucleotide during its formation and continuous replenishment afterwards.
- littlestymaar 8mo ago
  I wonder how much nucleotides present in asteroids in space survive the massive heating in the atmosphere and the crash though.
Paedor 8mo ago
20000 moles of length 45 nucleotides is 306 metric tons? Spread out over millions of years, that does seem completely feasible.
adgjlsfhk1 8mo ago
it's much more than 1 in 2^90. this specific 45 base sequence was found by random search which strongly implies that the odds of finding such a protein are much much higher (i.e. >2^-30) since the experiment probably only searched a couple million proteins
- cyberax 8mo ago
  (these are not proteins, these are RNA sequences) And it's likely that there are even smaller replicators but probably not much smaller. And there are likely more configurations among these 45 base-combinations that can self-replicate. It's also more likely that the first replicators were arrangements of multiple smaller molecules that can amplify themselves, and not just one large molecule. But even this longer sequence is well within the realm of synthesis by pure chance. RNA molecules can grow base-by-base, so a random walk model should eventually produce it.
- Kotlopou 8mo ago
  Actually, the search here is chemical -- you make a bunch of random small RNA sequences, then chemically replicate those that do what you want, and after a few cycles of this you find just a few sequences dominating the population. The pools can easily reach 10^14 examples and more, because you don't need a separate container/experiment for each one, but do it all together in one batch. The keyword is SELEX, a pretty cool idea: https://en.wikipedia.org/wiki/Systematic_evolution_of_ligands_by_exponential_enrichment https://en.wikipedia.org/wiki/Systematic_evolution_of_ligand...

by cyberax 8mo ago

jjk166 8mo ago

Note that the Bennu asteroid sample had approximately 5 nanomoles of nucleotides per gram, meaning 20,000 moles of nucleotides could be delivered by a single 4 million ton asteroid, which if it were a spherical carbonaceous chondrite would be about 183 meters in diameter. An asteroid about that size impacts earth roughly every 36,000 years, and that mass of meteor material falls to earth each century. If primordial earth's oceans had nucleotide concentrations comparable to Bennu, then there would be about 10^39 nucleotides in the ocean.

nkrisc 8mo ago
If raw materials isn’t the bottle neck for life every where, then what might it further down the line between oceans full of nucleotides and life? The oceans themselves?
- cousinbryce 8mo ago
  Temperature range and magnetic field are my first thoughts.
dekhn 8mo ago
I don't see any reason for the source molecules to come from space. We already know that nucleotides will spontaneously form and polymerize in conditions consistent with the early earth, and a meteorite origin just moves the source of those nucleotides elsewhere but doesn't answer how they formed.
- rolph 8mo ago
  space has been around for a lot longer than earth, its possible that inter planetary generation of nucleic acids may be primarily a matter of chemistry. Nucleobase synthesis in interstellar ices[2019] https://www.nature.com/articles/s41467-019-12404-1?error=server_error#Abs1 https://www.nature.com/articles/s41467-019-12404-1?error=ser... Chemistry of Abiotic Nucleotide Synthesis[2020] https://pubs.acs.org/doi/10.1021/acs.chemrev.9b00546 https://pubs.acs.org/doi/10.1021/acs.chemrev.9b00546
- heavyset_go 8mo ago
  It's possible (proto-)life evolved in the pre-Earth protoplanetary disk. If so, life might not require a special snowflake planet like Earth to develop. Development could be solar system-wide, and common in other early solar systems.
- jjk166 8mo ago
  Delivery by meteorites isn't necessarily the only or even primary source, but the fact is that it is a source we can directly observe, and it is a sufficient source. Earth's primordial chemistry likely did create more, but the existence of those conditions is theoretical, and such additional production need not be invoked to explain the needed level of abundance. Even a world with very different conditions from primordial Earth would likewise receive vast quantities of nucleotide during its formation and continuous replenishment afterwards.
littlestymaar 8mo ago
I wonder how much nucleotides present in asteroids in space survive the massive heating in the atmosphere and the crash though.

Paedor 8mo ago

20000 moles of length 45 nucleotides is 306 metric tons? Spread out over millions of years, that does seem completely feasible.

adgjlsfhk1 8mo ago

it's much more than 1 in 2^90. this specific 45 base sequence was found by random search which strongly implies that the odds of finding such a protein are much much higher (i.e. >2^-30) since the experiment probably only searched a couple million proteins

cyberax 8mo ago
(these are not proteins, these are RNA sequences) And it's likely that there are even smaller replicators but probably not much smaller. And there are likely more configurations among these 45 base-combinations that can self-replicate. It's also more likely that the first replicators were arrangements of multiple smaller molecules that can amplify themselves, and not just one large molecule. But even this longer sequence is well within the realm of synthesis by pure chance. RNA molecules can grow base-by-base, so a random walk model should eventually produce it.
Kotlopou 8mo ago
Actually, the search here is chemical -- you make a bunch of random small RNA sequences, then chemically replicate those that do what you want, and after a few cycles of this you find just a few sequences dominating the population. The pools can easily reach 10^14 examples and more, because you don't need a separate container/experiment for each one, but do it all together in one batch. The keyword is SELEX, a pretty cool idea: https://en.wikipedia.org/wiki/Systematic_evolution_of_ligands_by_exponential_enrichment https://en.wikipedia.org/wiki/Systematic_evolution_of_ligand...