exchemist

No, you've got it, that's the point. You obviously don't add the velocities, as you would in classical dynamics.

OK I give up.

You can only define a speed relative to some other object. So far the only objects you have mentioned are the two spacecraft. Is 99.999% of c measured relative to the other spacecraft or to something else? If the former, you have already stated the answer. If the latter you need to say what that something is. You could for example say each space craft approaches the same space station, from diametrically opposite directions, at 99.999% of c relative to the space station.

99.999% of c relative to what, though?

This looks like a ridiculous gimmick to me, designed to get silly people to waste their money while feeling somehow vaguely "green" as they do so. I'm tempted to suggest the "Y" in the brand name is a misprint. There's just no way having a thing like this bubbling away in a corner is going to give you measurably more oxygen, which in any case you don't need. As for the nebulous claim about capturing "pollutants", what pollutants are they talking about and what evidence is there that these algae will capture them?

OK I take your point. I had not looked into the sources they are relying on for the claim of low Mo in the pre-GOE oceans.

I've never heard this and it seems extraordinarily unlikely to be true. Can you cite any examples of this claim being made?

Well obviously life did not have to wait for nitrogenase before it could start. No one is making a claim of no fixed nitrogen, just that there was much much less and not enough to sustain a biosphere on anything like the scale of later epochs.

Hmm, I don't think I buy that explanation, for the simple reason that before the evolution of nitrogenase, life on Earth must have very sparse, constrained by........... the scarcity of fixed nitrogen. So the low Mo in the Archaean oceans can't be attributed to lifeforms scooping it all up. Life would have proliferated only after nitrogenase appeared. So for that hypothesis to work, one would expect to see a fall in Mo at a certain point. That would be dramatic evidence for the onset of nitrogenase-exploiting organisms, but it is not what they report. Mind you, it isn't clear to me exactly how they have deduced a low level of Mo in the Archaean oceans.

Sure. If you read the link, this is all gone into, but apparently there was very little Mo in the early oceans, hence the interesting question of how the first nitrogenase (or nitrogenase cofactor) was able to employ it. Reading more about all this, it seems that iron-sulphur complexes are widely prevalent in biochemistry, which is certainly suggestive of volcanic origins, though in the reducing environment pre-GOE, Fe(II) at least would apparently have been available in the oceans.

I admit I've slightly lost the plot on where we are these days on the various scenarios for abiogenesis. I had the idea thermal vents had gone out of fashion a bit for some reason, but I agree these heavy metal biochemistries suggest something like that. The use of sulphide sulphur is also a bit suggestive.

Yes, Loeb’s recent claims did indeed turn out to be a load of, well, spherules. 😆 Not surprising people start to wonder if he may have a personal agenda that is warping his judgement. Personally, I suspect Loeb has actually become a crackpot.

This has prompted me to revise the bonding scheme for transition metals with carbon monoxide: https://en.wikipedia.org/wiki/Metal_carbonyl This involves a dative σ-bond from the lone pair on C to the metal and a π back bond from occupied d orbitals on the metal to low-lying π* antibonding orbitals on CO. So donation of an electron pair in both directions, preserving neutrality overall. The effect of the involvement of the antibonding orbital is to weaken the C≡O bond (nominally triple in the free CO molecule) and strengthen the M-C bond. This I think gives a clue as to how such metal atoms can weaken the N≡N triple bond (preparatory to adding H atoms), N≡N being isoelectronic with C≡O. It starts to become clearer........ N.B. The need for an electron pair in a metal d-orbital to make the back-bond requires the metal to be in a low oxidation state.

I haven't seen any mention of Ni in the paper or the Wiki article on nitrogenases that I quickly read to try to understand more about them. But it is interesting I think to reflect on how many of these heavy metals play such critical roles in life. We often think in terms of H, C, N, O, S, and P, plus a handful of s-block cations, but actually a huge array of heavy elements gets pressed into service as well. Their multiple oxidation states and d orbitals turn out to be pretty important.

Yes I think there is a reference in the paper on the other thread about the means organisms use to keep oxygen away from the active centre. I can imagine that a metal site that can bind N2 might also bind O2 - even might prefer to do so - which would stop it working. (Reminiscent of how carbon monoxide blocks haemoglobin, though perhaps not an exact parallel.) In chemical terms it's really fascinating, since the N-N triple bond is so notoriously hard to break.

OK, I've now started a thread on the evolution of nitrogenase, in the Evolution section of Biology. I knew nothing about this at all until a few days ago. 😀

Following on from @Moontanman's thread on a new nitrogen-fixing organelle, I started wondering how biological nitrogen fixation first arose at the dawn of life. I found the linked paper, which I thought very interesting on the subject: https://www.sciencedirect.com/science/article/pii/S0966842X23000914 The writers focus on the metal atoms (or metal/sulphide complexes) which are at the heart of nitrogenases, which can bind nitrogen, lower the strength of the triple bond and progressively add H+ and electrons to form eventually 2 molecules of ammonia. There are 3 variants of nitrogenase, one using just Fe, one using Fe and Mo (molybdenum) and one using Fe and V (vanadium). I was surprised to see these 2 transition metals have such a biologically important role, but there you go. It seems there is evidence the first nitrogenase appeared in the Archaean, before the Great Oxygenation Event (i.e. global-scale photosynthesis), which I suppose is not a surprise, seeing as a lot of life would be needed to geo-engineer the planet, and that would require a lot of fixed nitrogen. They suggest that, before the GOE, there would have been a lot of Fe²⁺ in the oceans, whereas under oxidising conditions this would go to Fe³⁺, the salts of which tend to precipitate from aqueous solution, so would be less bio-available. So a system incorporating Fe is not hard to explain. Curiously, though, phylogenetic analysis suggests that the version incorporating Mo as well as Fe was the first to appear, even though the concentration of Mo in the early ocean was apparently very low. That version has better kinetics, which may have favoured it, but it still leaves open the issue of where the Mo came from. They speculate that there may have been higher local concentrations in the zones where the first nitrogenase arose, perhaps in hydrothermal vents. But this is very much open-ended and needs further research. By the way I found the chemistry of these nitrogenases really interesting. There seems to be some very unusual chemistry, involving bridged hydrides to supply the extra electrons needed for the reduction. But that's another subject. It seems the evidence is that nitrogenases are an "evolutionary singularity", meaning this little family of 3 closely related variants, using the 3 metal combinations mentioned, seems to have evolved once only in the whole history of life on Earth. But absolutely vital to the whole enterprise of course.

OK, but telephone numbers like this don't tell us a great deal until put into context. What concentration of NOx is this thought to have generated? Especially in the marine environment where life is thought to have started.

Hardly enough for much, I'd have thought. But maybe just enough to get some biochemistry started. I suspect N availability would have been one of the key constraints at the beginning. But I may have found a good paper on this. Let me read it and start a new thread if it's what I'm after.

Ah that's interesting. I didn't realise thermal conductivity of gases was proportional to specific heat capacity. So it is something to do with 3/2R rather than 5/2R, after all.

Actually this prompted me to wonder about where the "fixed", i.e. not molecular N2, nitrogen came from at the origin of life. It's impossible to construct terrestrial biochemistry without a source of this, whether from nitrites, nitrates or ammonia or something like that. Could be worth starting a thread on it.........I'll do some digging.

Agreed. I was referring to electrolysis processes involving CO2 such as those in the Wiki article, not to direct splitting into C and O.

OK I just about follow this, but the overall stoichiometry and thermodynamics won't be affected by the mechanism, even if various separate processes and intermediates are involved. If the starting material is carbohydrate and the waste products are hydrogen and CO2, there has to be a notional reaction scheme that accounts stoichiometrically for the relation between reactants and eventual products. That's the bit I want to understand.

Ah yes, higher mass would reduce diffusion rate. Re sound, I suppose an interface with a denser medium would create some partial reflection. But that’s just a guess.

I’ve just had some new windows fitted which have argon between the two layers of glass. I can’t find a good explanation for this on line. I would expect the heat capacity to be lower than for air, as argon is monatomic, but this does not seem likely to be relevant. Would argon conduct heat less well and if so, why? Some “explanations” say the higher density of argon is an advantage but I can’t immediately see why. I can see that an inert gas would not react over time with components of the frame and seals, but this does not seem to be the chief reason for its use. Lower heat and sound conduction seem to be the reasons given, but why would this be? Does anyone know?