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Comment by andrewla | Hacker News Reader

It's a remarkable thing to step back for a second and realize that while we try to figure out the exact impact of a parts-per-million change in CO2 concentration, that it's astonishing that CO2 is not 20% of the atmosphere, that the only thing keeping O2 in the atmosphere at all is the large-scale actions of living things. [1]

The fact that living organisms are responsible for something so large seems almost dumbfounding -- planets are big, atmospheres are big, and life is small; what is a pool of algae compared to a mountain, etc. But even such a basic thing as "the only reason we can have something as fundamental as FIRE is because of living things" is a bit of a mindblowing realization.

[1] probably not literally true; if you eliminated all life on earth then most of the O2 would probably be sequestered in oxides rather than remaining resident as CO2, but still. Although I guess a lot of non-living organic matter would eventually burn away as long as there is oxygen to support combustion.

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I'm pretty sure it is literally true that the oxygen in the atmosphere is there only because living things keep putting it there. You're right that without life, it would be sequestered in oxides pretty quickly. That's the local minima for energy dissipation. Life is good at breaking those minimas for cyclic matter dissipation. If there was a natural source for oxygen, it would have to come from some sort of cycle in order to be maintained, and there's not a energetically favorable cycle for that.

It's why it makes a good biomarker when looking at exoplanets. If we find an exoplanet with high amounts of oxygen in the atmosphere, we can be fairly confident

Was much more likely true until a week ago, but now there’s a legit competing hypothesis :) https://www.nature.com/articles/s41561-024-01480-8

Yeah, that's an exciting discovery. I was excited by this, because I believe it demonstrates a dissipative pathway that could have contributed to abiogenesis. Energy gradients are a driver of emergent complexity.

Yep, exactly what I thought when reading Lane! But what would be the quantitative contribution of benthic O2?

I’m surprised by this statement.

Here is a quote from Nick Lane’s great text: Power, Sex, Suicide (p 153):

> The early Earth, as envisaged by [Michael J] Russell, is a giant electrochemical cell, which depends in the power of the sun to oxidize the oceans. UV rays split water and oxidize iron. Hydrogen, released from the water, is so light that it is not retained by gravity, and evaporates into space. The oceans become gradually oxidized relative to the more reduced conditions of the mantle.”

Lanes cites this paper “On the origins of cells: A hypothesis for the evolutionary transition from abiotic to nucleated cells”, 2003, by Martin and Russell

https://pubmed.ncbi.nlm.nih.gov/12594918/

Am I missing something? This text forces me to assume that solar UV splitting water is the cause of the O2 atmospheric flooding.

And not true at all that all organisms need O2 to pump protons. Microbes have quite a few alternative ways. Even we do when we run the Krebs cycle backwards.

I'm currently reading another of his books, Oxygen: The Molecule that made the World, which unsurprisingly has lots more about this topic.

I'm a huge fan of Nick Lane, and I'm not an expert, so I may have misunderstood. I have not read "Power, Sex, Suicide" but have read "The vital question", "transformer," and most importantly in this context, "Oxygen."

My understanding, which could absolutely be wrong, is that there are pathways to where Oxygen can be generated without life, but for it to be maintained at high levels of concentration over time, that takes life. I would definitely defer to whatever Nick Lane has to say about it.

Here's the full text of the "On the origins of cells..." paper via sci-hub:

https://sci-hub.se/10.1098/rstb.2002.1183

There's nothing in it about ultraviolet splitting of water or oceanic oxidation. If Nick Lane meant to paraphrase the paper in that cited passage, he did a poor job.

Direct UV homolysis of water to release hydrogen requires a photon with more than 6.5 electron volts of energy [1], corresponding to a wavelength of 190 nm or shorter. As you can see here, solar irradiance is extremely low at wavelengths shorter than 240 nm:

https://en.wikipedia.org/wiki/Solar_irradiance#/media/File:S...

There isn't enough energetic UV radiation emitted from the sun to directly oxygenate the Earth via water homolysis. It might be possible for an exoplanet in orbit around a hotter star that emits more energetic UV.

EDIT: I forgot to account that the sun may have had a very different UV profile billions of years ago.

"UV radiation from the young Sun and oxygen and ozone levels in the prebiological palaeoatmosphere"

https://sci-hub.se/10.1038/296816a0

UV measurements of young T-Tauri stars, resembling the Sun at an age of a few million years, have recently been made with the International Ultraviolet Explorer. They indicate that young stars emit up to 10^4 times more UV than the present Sun.

[1] https://en.wikipedia.org/wiki/Photocatalytic_water_splitting...

To reduce hydrogen, something needs to be oxidized, but it doesn't need to be oxygen. E.g. you could get more metal oxides. Not my field exactly, so I don't know either relative abundances of different stuff in early oceans or the exact ranking of which would be most readily oxidized, but that could explain the discrepancy.

Edit: rereading the passage you quoted does make me think that metal oxides are the important factor here.

I've never understood applying this idea to exoplanets. What if the life there puts sulfur into the atmosphere instead of oxygen? Why would the life elsewhere look anything like the life here in terms of gas use, etc

The point is that if a planet has oxygen, it's a potential marker for life. No one is claiming that a planet that lacks oxygen in the atmosphere must necessarily be lifeless.

It's true that if life exists on other planets, it may not look exactly like life here. But it's also true that there are a small number of elements in the periodic table, and only so many of those are even relatively common in the universe, and only so many of those are useful for reactions, etc, etc. The things that life on our planet use seem to be some of the most obvious candidates to use, if not the most obvious, so if life exists on other planets, it would be surprising if the things that we use are unique or even uncommon across the universe.

Bc the same physics apply there

> If there was a natural source for oxygen, it would have to come from some sort of cycle in order to be maintained, and there's not a energetically favorable cycle for that.

Life is the energetically favorable natural source of oxygen. Or more accurately, it's thermodynamically favorable.

Photosynthesis uses light to create intermediate products (eg carbohydrates) which are later metabolized in a way that releases chemical energy and heat. If you consider the incoming light as part of a system including Earth, and not as something acting on a system, you can see that it ultimately increases entropy despite being chemically endothermic. It converts fewer, higher energy photons (in the visible light range) into a higher number of lower energy photons (most of the energy being infrared as a result of the incremental increase in blackbody radiation from the heat generated from metabolism of the intermediate food products) and drives the conversion of simple chemical compounds like urea into highly complex ones like proteins.

In other words, the oxygen in the atmosphere is an energetic byproduct of all the light colliding with the surface of earth. There are processes which do essentially the same thing without life. The atmosphere of the moon includes trace amounts of elemental sodium gas from very high energy photons colliding with sodium rocks in a way that cleaves away sodium ions. And the atmosphere of earth contains the even-more-reactive form of oxygen Ozone because of ultraviolet light doing the same thing to molecular oxygen.

I don't think this interpretation is correct -- at least on Earth, there are no fundamental geophysical processes which can sustain oxygen in the atmosphere at anything but trace levels.

Producing oxygen is not energetically favorable under basically any circumstances. Free O2 production was "invented" (as it were) as a way of murdering almost all other life on earth at the time. It's a mistake to look at life in a thermodynamic equilibrium sense unless your time scales are ridiculously long (i.e. burn-out-of-the-sun long).

Yes, you are exactly right, that is my awkward wording for exactly the point you're trying to make. I should have added, "besides life" to the end of my sentence.

The fact that there is not a more thermodynamically favorable pathway besides life is probably what allowed life to emerge in the first place. If there was a more efficient way to dissipate that energy, earth would probably be dead.

Or put another way: life emerged because it was the most thermodynamically favorable way to dissipate the available free energy in our system.

You are right that life does not provide any source of energy, so any results of life activity could also appear when there is no life, including free elemental oxygen.

What life does, is changing by many orders of magnitude the speed of certain chemical reactions, including the reaction by which water is decomposed, releasing free dioxygen.

The concentration of any substance in our environment is normally an equilibrium concentration, which is determined by the speeds of the chemical reactions that produce and that consume that substance.

On a planet without life, the speed by which the stellar light produces free dioxygen is very small in comparison with the speed at which the dioxygen is consumed by oxidizing various substances available in the environment. Therefore the concentration of dioxygen stays extremely small.

On a planet with life forms that have developed catalysts (enzymes) for oxygenic phototrophy, like the blue-green algae (cyanobacteria) of Earth, the speed of producing dioxygen increases by many orders of magnitude. The consequence is that the ambient concentration of dioxygen increases until the speed by which it is consumed balances the production speed. The existing dioxygen is consumed by the oxidation of the magmatic rocks that are brought from higher depth to the Earth surface, by the respiration of a number of living beings that increases with the available amount of dioxygen, by fires and nowadays by the oxidation of various reduced substances, such as metals, which are produced by human industry.

In conclusion, life alters the speeds by which various chemical substances are produced or consumed, and this greatly alters the equilibrium concentrations of those substances in any environment where life exists.

> planets are big, atmospheres are big, and life is small;

And time is long.

The consensus is still that the oxygenation of Earth's atmosphere took "at least 400 million years". A lot of that is due to the "great rust", i.e. minerals that would take oxygen out of the air had to first exhaust their capacity to oxidise. This took "nearly a billion years".

Iron ore deposits are from the seabed of this period.

See:

https://en.wikipedia.org/wiki/Great_Oxidation_Event

https://en.wikipedia.org/wiki/Banded_iron_formation

> Iron ore deposits are from the seabed of this period.

Many are, but some are more recent.

https://en.wikipedia.org/wiki/Chilean_Iron_Belt

https://www.nature.com/articles/s41467-023-43655-8

That was pretty interesting to me and perhaps changes our idea of how the great oxidation went a bit:

(Evidence of dark oxygen production at the abyssal seafloor)

https://www.nature.com/articles/s41561-024-01480-8

Some of those mountains are made of calcites and dolomites and bioturbated with trillions of miles of burrowing shrimp tunnels. The Biosphere is certainly as significant a process as any other process acting at or near the surface of the earth.

The idea in my head is that life is anti-entropy. Maybe my idea is wrong? maybe it just has different signatures at different times?

One definition I've ever heard for life is that it's a process which increases the entropy around itself in order to decrease the entropy within itself. It disorders the world around it to order itself.

that might be true. And maybe lower life forms are destroyed to create higher (much less entropic) life forms.

Nearly all life gets consumed by some other form of life eventually. Often it's the bacteria and fungi and insects doing the consuming of what we might consider more sophisticated organisms. The negative entropy - all the useful molecules concentrated and precisely ordered - can be seen as the thing being consumed. Same goes for chemical or energy gradients like around deep water thermal vents or photosynthesis.

If you kill all life on earth, I assume all dead biomass would oxidize into CO2.

Though I'm not sure what processes would do that. Without microorganisms, nothing rots. Lightning would eventually burn down most forests, but maybe everything else would just lie where it fell for ever.

"Without microorganisms, nothing rots."

That is not (quite) true. The lifeless bodies of flora and fauna won't rot, but they will decay. Macro-molecules (like proteins), the basis for all life, are fragile and easy to break down due to a range of physical causes, most likely of which is just the non-cryogenic temperature. Smaller organic molecules are more sturdy and will last longer, but in the long term they'll end up under heavy layers of sediments and turn to fossil fuel (coal & oil).

That makes sense, but I don't think much of the broken down molecules oxidizes.

Which is also what "turn to fossil fuel" implies.

Let me share a twist on this train if thought that I've had recently.

The nature of the Earth's atmosphere, surface, oceans, and much of the subsurface is entirely the product of a single cell. A single cell lead to more cells which eventually evolved into different forms and became multicellular and so on and so forth until the earth was covered in all kinds of shapes and sizes of life and the landscape was permanently changed.

All that from one cell.

You and I are composed of trillions of these things and we're able to do incredible things with them, but at the same time our power is much more limited than that of the single cell that created all of life. We can do incredible things with our bodies but we lack the ability to completely control even a single cell in our body. As such a single cell can go rogue and kill you with cancer, or despite your best efforts to nourish, heal and exercise your cells you will eventually die.

Imagine if it wasn't so.

Imagine if you could control but a single long lived cell in your body. What could you do with that? Anything. Nothing could stop you. You could travel to the deepest depths as a whale or soar to the highest heights as an eagle. You could spawn a mass organism larger than Pando, or evolve something novel that would go to space.

So imagine if someone locked you deep in a dark prison in solitary confinement and you could through something akin to meditation come to control a single cell in your body. No prison could hold you.

What happens when we achieve mastery over ourselves in such a way through technology? Will we allow individuals this level of control over their own cells? Can we stop them?

This reminds me: Stem cells. Whatever happened with that?

Oh, lots. We are slowly but steadily making more advances with learning how to reprogram cells and get those cells to grow and divide and turn into things are sort of like different body parts. It's not really like sci-fi yet but it is honestly starting to get a bit weird. See the new book The Master Builder by Alfonso Arias for some recent info.

> our power is much more limited than that of the single cell that created all of life

Is it? That single cell had 3.5 billion years of almost-exponential growth to do its thing. We've been on this planet for something like 100,000 to 1 million years, depending on how you count, and we've had a pretty damn big impact on its atmosphere, surface, oceans, and even subsurface; most of that in the last century. Imagine how much we could change the Earth in the next billion. Our power seems terrifying in comparison.

> We can do incredible things with our bodies but we lack the ability to completely control even a single cell in our body

That's only because you've snuck in a very particular definition of "we" here. Single cells in my body are happily controlling themselves as they always have.

> Imagine if you could control but a single long lived cell in your body. What could you do with that? Anything. Nothing could stop you. You could travel to the deepest depths as a whale or soar to the highest heights as an eagle.

Could you? By your accounting, isn't your original single cell (let's call it LUCA) already doing that now? That little archaebacterium from 3.5 billion years ago must be pretty proud of itself. Aren't you essentially saying: hey, you might end up with a lot of descendants, and they might do cool things. Yup. That's true. "Control" never really played into it at all. See the funky accounting of "we" and "you" you're doing here? It's actually LUCA going to space, isn't it? Or is it us? Or just them? Who are you actually talking about here?

> So imagine if someone locked you deep in a dark prison in solitary confinement and you could through something akin to meditation come to control a single cell in your body.

Yeah, but, y'know, you can't, because the "you" you're thinking of is an emergent property of the collective action of trillions of these cells, with virtually no resemblance to the forces that individual cells use to make decisions.

> No prison could hold you.

There's already no prison that could hold me for 3.5 billion years. Except a black hole, I guess. And I've already spawned some descendants, so by your accounting, you'd have to imprison them all too.

> Will we allow individuals this level of control over their own cells? Can we stop them?

What happens when humanity develops The Super Encaptropositronator? That can do ANYTHING? Are we just going to let ANYONE use the Super Encaptropositronator that can do LITERALLY ANYTHING!? IMAGINE THE HORROR! It might make a decent sci-fi book though.

I finally understand the prisoner scene in Akira

> "the only reason we can have something as fundamental as FIRE is because of living things" is a bit of a mindblowing realization.

I am fairly confident living things did not create FIRE.

Well, we (broadly speaking) did not create the concept of a plasma phase of matter, but fire as we know it is only possible because of free oxygen. Fire, for the most part, is just another name for rapid oxidation.

Even some things that can burn without air (e.g. magnesium) typically only burn because they are so hot that they cause H2O to separate.

Obviously stars exist, so there are other ways of getting to plasma, but oxygen is what makes terrestrial fires possible.

So yes -- living things created fire!

> Even some things that can burn without air (e.g. magnesium) typically only burn because they are so hot that they cause H2O to separate.

I'm not positive about magnesium, but also most of them only burn because we've converted them to materials that don't exist in nature. Eg it'll only be found as oxides (ie already burnt) and then we put some energy or chemicals in to get the form we want.

If it _can_ oxidize as found in nature, there has to be some good reason it didn't already do it over ~billions of years.

Bare rocks and water don’t burn, they are already oxidized. Life chemically reduces CO2, providing material than can support combustion.

Well, we didn't start the FIRE. It was always burning since the world's been turning.

Without living things, who would retire early? The markets aren't going to trade themselves.

> The fact that living organisms are responsible for something so large

how do you separate living and non living things? (https://en.wikipedia.org/wiki/Life#Challenge)

everything is responsible for something.

They meant puny gooey things.

Yes, I figured that's about the level of sophistication:)

It was a poetic reflection. Don't worry, I didn't always get this sort of thing either. Maybe one day you too will learn to enjoy it :-)

The goal was to move from empty poetry to actually interesting science oriented discussion. Maybe one day you learn to enjoy those ;)

I'm currently reading Biological Science by Scott Freeman on my day off, and later on I'll finish off Special relativity and classical field theory by Leonard Susskind. If you consider poetry empty, perhaps it is you who are missing out on something. I myself do enjoy both ;-)

Not all poetry is empty, but some poetry is empty

Good on your reading progress, now all that's left is to engage in interesting conversations about those topics;)

I'm quite picky on whom to engage in interesting conversations with.

Same except I guess the difference between us is that I am picky regarding substance (what it is about) not whom it is with.

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