That they say it existed in the middle Hadean is striking. It was grabbing a toehold even when our world was a literal hellscape.
I think it increasingly likely that DNA first formed in space when the ambient temperature of the universe allowed liquid water. How else does a LUCA appear as if life on earth was a fait accompli, in the wake of a collision with another planet no less.
The issue is that of concentration. You need some kind of biogeochemical cycle that creates a concentration gradient. Otherwise the basic components are too diffuse to do anything meaningful.
I still lean into the "volitile ice balls" theory. NHx, NOx, Ox, etc. as volatile ices on asteroids in orbits where the iterate between freezing and melting. Moving between freezing and melting creates the biogeochemical cycle necessary to concentrate the basic elements sufficiently to be meaningful.
It was grabbing a toehold even when our world was a literal hellscape.
Actually this makes sense in the context of autocatalytic sets hypothesis - you'd need large variety of inorganic compounds and a strong energy gradient to kickstart a metabolism.
well, we need RNA before DNA. and we already have rna origin theories, so no, space dna doesn't seem to fit there as an emergent property of rna to self replicate.
What do you mean liquid water in space? Liquid water doesn't exist at low pressures, so you also need a somewhat pressurized environment like an atmosphere
I could be mistaken but I believe the hypothesis is that at one point the universe had an average temperature and matter distribution (pressure) to make it so that in most or at least a large portion of the universe it was significantly easier for organic molecules to start forming including the building blocks of DNA and then when it cooled/expanded some of that organic matter made its way to earth to eventually turn into life.
Definitely the latter. Eventually, Picard comes to realize the situation he helped create and makes decisions that stop any of what he witnessed occur. Q was just "nudging" him in the right direction.
No, since everything we know about the LUCA is from its descendants. Microorganisms without descendants wouldn’t leave behind any evidence of their existence.
Using genetics alone, sure. But maybe there’s fossil or geochemical evidence of early organisms not belonging to any of the three surviving domains—or maybe we could estimate it just from statistics.
Wouldn't LUCA by definition be the last common ancestor of every organism of which we have evidence? If so then by definition we wouldn't have evidence of those other lineages. Or is it just the last common ancestor of everything currently alive?
The definition I’ve seen is the last common ancestor of procaryotes, eucaryotes, and archaea—which doesn’t strictly rule out the possibility of extinct domains whose existence we might infer.
And actually, there’s evidence of non-LUCA-descended organisms mentioned right in the paper: the other organisms that constituted the ecosystem of which LUCA was a part, whose existence (and some characteristics) could be inferred from LUCA’s metabolism and immune system.
