[ExI] Abiogenesis

[Stuart LaForge]

Quoting John Clark:

> ----- Forwarded Message ----- From: John Clark  
> <johnkclark at gmail.com>To: ExI chat list  
> <extropy-chat at lists.extropy.org>Sent: Saturday, February 9, 2019,  
> 3:17:08 PM PSTSubject: Re: [ExI] Abiogenesis
>  Stuart LaForge <avant at sollegro.com> wrote:
>
>
>> They have found complex chiral organic compounds in the center of the galaxy
>
> They found the chiral molecule Propylene oxide, but as far as I know  
> they did not find more of the right handed version than the left  
> handed version.

Thanks for catching that. I somehow missed that since they only  
mention it toward the end and the rest of the article made it sound  
like they had detected asymmetric molecules.

>> they think meteorites brought the chiral molecules to Earth.
>
> I'm sure that true, with the exception of glycine the simplest amino  
> acid all of them are chiral and 52 have been found in meteorites,  
> but 33 of those are not among the 20 amino acids that life uses. And  
> life only uses left handed amino acids (and right handed sugars) and  
> most meteorites don't have more left handed amino acids than right,  
> but one was found that did and it's hard to think how that could be  
> without polarized light:

My hypothesis isn't about how amino acids got here but about how only  
one of two stereoisomers became so predominate.

>
> https://www.nasa.gov/topics/solarsystem/features/life-turned-left.html
>
> However such a asymmetrical meteorite is rare and it shouldn't be if  
> the light came from the galactic center, so I think it's more likely  
> the polarized light came from something local and much smaller than  
> the galactic center, a nearby neutron star perhaps.

Maybe but there are over a billion neutron stars in our galaxy so I  
would not call them rare. If they can enrich for homochiral molecules  
at interstellar distances, then life should be far more common than it  
seems to be. Whereas the galactic center would have only have affected  
a narrow swath of stars in the disk where the flux density was just  
right. Too far and not enough effect, too close and you photolyze both  
stereoisomers.

> Or maybe astronomy is not needed at all to explanation the  
> lopsidedness in the chemistry of the biosphere; as far as we know  
> right handed molecules would work as well as left so maybe LUCA, the  
> last universal common ancestor, just happened to use left handed  
> amino acids and once such a standard had been established there was  
> no reason to change it.

Once life got up and running, then I could see an enzymatic-type  
chemical process selecting for homochiral molecules from a mixed pool.  
But I don't see how life could have gotten up and running in the first  
place in a 50-50 equilibrium environment. It is neither entropically  
or enthalpically favored so it would require something like Maxwell's  
demon. Astronomical sources would have the energy to enthalpically  
force such a reaction.


> Speaking of the galactic center, all galaxies have black holes at  
> their centers and on average they have about .1% of the mass of  
> the galaxy they're in. our Milky Way galaxy has the mass of 700  
> billion Suns so you'd think its central Black Hole should have a  
> mass of about 700 million suns, but in fact it's only 4 million. So  
> for some reason Sagittarius A is freakishly small and that may be a  
> good thing because if a galactic center where to turn into a full  
> power quasar it sterilize the entire galaxy it was in.

You know, I remember thinking the same thing when I first compared our  
galaxy to Andromeda. I think you were right earlier when you said  
something to the effect that our galaxy is weird. If quasars tend to  
sterilize their galaxies, then things are liable to get a bit hectic  
in about 4 billion years when the Andromeda and Milky Way galaxies  
collide. Galaxy collisions tend to provide the black holes of both  
galaxies with new fuel until they settle down and collide themselves.  
In any case, I agree that the galaxy going quasar on us is an  
existential risk.

Stuart LaForge