Phosphorus, the origin of life, and the Fermi paradox

[arkuat]

So for a long time now, I've been poo-pooing the idea that life originated in shoreside tide pools, because I had adopted the opinion that life originated in deep suboceanic volcanic vents.

But it turns out that life probably formed before the ocean was even fully formed (i. e. early in the stages in which Hadean Earth was still outgassing lots of water and/or hadn't received all of its cometary intake yet), so it looks like the actual truth is somewhere in between the two ideas: lakes and ponds forming on the surface of fresh hot lava on top of barely-formed crust VERY early in the stages of cooling. It's a little like an underwater volcanic vent, and it's a little like a tidepool!

Here's an interesting paper that helped lead me to this conclusion:

Toner, J. D. and D. C. Catling (2019), A carbonate-rich lake solution to the phosphate problem of the origin of life. Proceedings of the National Academy of Sciences, 1-6. DOI: https://doi.org/10.1073/pnas.1916109117

(ETA: for those who don't know, phosphorus is needed for ATP and ADP, which all living things (yes, all) use to store and deploy energy internally, and also for RNA and DNA (yes, all), which you probably know about, and is also needed for cellular and intercellular membranes (again, yes, all such membranes in every organism) in the form of phospholipids. So, about as fundamental as carbon in its own way, but much less common than carbon. Also, it's a lot harder for stars to make than most atoms as light, for nuclear astrophysics reasons that I've read about but barely understand myself.)

And here's a youtube video that got me thinking about the whole phosphorus problem (including the problem of its nucleosynthesis), and suggests it as the resolution of the Fermi paradox:

https://www.youtube.com/watch?v=oPU9jeQbTOU

Looks as if we may have gotten over the Great Filter hump a long damn time ago. Unfortunately this means that aliens are gonna be pretty scarce, and it definitely shores up the rare Earth hypothesis (i. e. the Solar system is probably unusually enriched in phosphorus).

Comments

[quadong]

The Fermi Paradox is interesting to me. I know something about nucleosynthesis, but an not an expert. I'm not at all clear on this claim that most heavy elements come from neutron star mergers. I should look into that. They are much rarer than supernovas, so that implies that they are much more efficient at either making or dispersing the elements they make. Unfortunately, pop sci videos and articles just present things as hard facts, whether or not they are very uncertain. Then later they sometimes tell you the opposite thing and you don't know why.

The "great filter" hypothesis being only kinda a general idea in the first place, I wouldn't assume there's only one. It's true that in physical systems, usually one effect dominates, but let's not assume that nuclear war isn't a problem yet.

[arkuat]

Neutron star mergers are not well understood yet, but since they probably spatter a lot of neutronium fragments, it's natural to think of them as the source of most stuff that is like uranium and thorium. His claim about such mergers is pretty irrelevant to the main drift of that video, since phosphorus is a light element mostly made (I'm pretty sure) in supernovas, not kilonovas.
I believe phosphorus is thought to result from decay of an isotope of silicon that gets one-too-many neutrons added to it during the supernova flux.

I would never argue that nuclear war isn't a problem yet, especially not with the climate catastrophe still playing out! I just spent some time (too much, probably) engaging with Great Filter theorists 20 years ago, and some of them liked to press extremely depressing arguments about inevitability which just don't look so inevitable to me anymore.

[quadong]

Sure sure. I think it's mostly made in lighter stars that don't explode and so it then just sits there. It's the product of production and dispersal that makes it a complicated question, which was what I was thinking about.

[arkuat]

Yeah, I've been wondering about that "product of production and dispersal" thing for various elements for many years now (mostly because of Fermi paradox), but don't have as many useful tools for doing so as you probably do.

Mostly it has been an occasional search for freely available papers on nucleosynthesis that use the word "kinetics" in its chemistry sense, but in the context of nucleosynthesis (and dispersal) rather than chemistry. Doesn't come up much, as I'm not sure the chemistry sense of "kinetics" has crossed over into nucleosynthesis astrophysics at all. Few seem to think there is enough data gathered yet for anyone to have firm opinions about such things anyway, is the conclusion that I've drawn so far.

Oh, yeah, and metallicity gradients! Finding out what I could about metallicity gradients was the most fruitful course for a while, but it turns out not that much is really known about them yet. I mean, all the theories are controversial. The galaxy people get very uptight about them.

[quadong]

I don't think that nuclear physicists use the word "kinetics" in that sense, or not often. There's a lot of work being done these days to measure nuclear reactions thought to be possibly important in stellar nucleosynthesis. It turns out the tricky part (one tricky part, anyway) is that the energies in stars are much *lower* than what we usually use in the lab. As you might expect, this means the reactions don't happen as much. They become important in stars because stars have a lot of matter and burn for a long time. To see the same reactions, at the same energies, on earth, people do counter-intuitive things like building small particle accelerators underground, because the reactions are so rare that the background on the surface would be overwhelming.

[arkuat]

Now that last bit is some really cool stuff that I had no idea about. Thanks.

[bibliofile]

You are way ahead of me on all of these topics, but it's still an interesting read. I was never much for biology, so I didn't know about phosporous. Cool. Thanks!

[quadong]

I am still thinking about this. Do you understand why ATP is universally used for energy storage? Is there some obvious reason why no other molecule could serve this purpose? Maybe "obvious" is too much to hope for. Is there some reason that anyone understands?

Of course, as an arrogant physicist, I ignored all biology things in school. (Exaggeration, but nearly true.) I gather from Wikipedia that the reason ATP/ADP works is that the phosphate group is relatively easy to pop on and off, and (in some way that I have no handle on) relatively easy to derive energy from in a useful way when popped off. That must be a pretty tall order while also requiring that both molecules are stable when not in use. So I can tentatively believe that the number of viable energy storage molecules is small, possibly one.

Still... on a planet without abundant phosphorus, is it clearly impossible that no calcium/sodium/magnesium/sulfur group could accomplish the same thing? Those are all available in higher or similar proportions to phosphorus in the Earth's crust and the (modern) oceans.

As I've posted here, I *might* be working on solar neutrinos, which are ever so tenuously connected to this question. :-)

[arkuat]

Well, I switched my major to humanities before I got around to taking physical chemistry, so I doubt I know anything you don't already know. The details of the behavior of ADP/ATP are totally p-chem even if it is mostly of interest to molecular biologists.

For me, though, it's not just the universality of ADP/ATP, it's the triple coincidence that phosphorus is required for that, *and* for the phospholipid-bilayer membrane incorporated into all eukaryote organelles (and prokaryote cell membranes also), *and* for the backbone of nucleic acids, both RNA and DNA. Of the three, I'm guessing the phospholipid bilayer came first.

I don't know if anyone has done any experiments trying to see if you can make a membranous lipid bilayer using a sulfate or nitrate group where we have the phosphate group in our biological membranes, but for instance, consider that nitric acid and sulfuric acid are *much* stronger acids than phosphoric acid.

[calimac]

I read the suboceanic vent theory in Nick Lane's The Vital Question and it sounded plausible. What the tidepool theory established was that it was easy to build complex structures out of simple ones spontaneously with just a little application of energy. That was an important step in the study of evolution.

I am inclined, without proof, towards the view that life was a freak occurrence that hasn't happened elsewhere, but I'm uneasy about using arguments like the universality of phosphorus as evidence for it. That's universal in earth-based life; if there's life on other planets, it may have come into being in ways that we haven't even imagined, and the limitations we see as universal may not even apply.

[arkuat]

Evidence for "a long time now": http://www.cryonet.org/cgi-bin/dsp.cgi?msg=5540

[arkuat]

Just gotta add that my main source of information when I wrote the above cryonet post (yeah, the '90s were weird) was The Alchemy of the Heavens by Ken Croswell. Nowadays, my main source when investigating questions of this kind is Searching for the Oldest Stars by Anna Frebel. I just noticed, when I went to look to make sure I was spelling the citations properly, that they are sitting right next to one another on my bookshelf, cover to cover. They're both very good books, although Croswell's is so sadly dated that it's nothing but a history of science work now. History of science has always been pretty cool in my book though, since I ended up as a history major.