Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: set fair on 29/07/2023 04:40:33
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Googling this, the answer given is theat it came from photosynthesis, originally from cynobacteria. My problem with this, is that if this were the case, then there should be enough oil & fossil fuel to use up all the oxygen and there doesn't seem to be anywhere near enough to do this.
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Photosynthesis uses carbon dioxide and water. Before there was much oxygen in the Earth's atmosphere, there would still have been a lot of carbon dioxide and water present. Fossil fuels need not have any connection, especially since only a minority of every organism to ever live has ended up as fossil fuels. Much of the material has been recycled over the eons.
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There are vast quantities of carbon sequestered in geology that is not economic to harvest.
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Like the whole of the south of England, for instance. Chalk in the south, coal (now irrecoverable) in the north, oil under the sea. This island is all about carbon sequestration!
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Chalk does not count as carbon sequestration in the OP's context as it is a carbonate which has not been reduced from co2. Another pedantic win!
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But chalk is the sediment of plankton skeletons, and plankton ecology begins with photosynthetic phytoplankton, including cyanobacteria.
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Yes Alan, you are 100% right on what you say but that is not the point. The OP was asking where is all the carbon, in reduced form, that would match the amount of oxygen in the atmosphere. co2 is carbon in oxidised form and the marine carbonate is produced directly from atmospheric co2 dissolved in seawater( unless I am greatly mistaken, not being a marine scientist, maybe BC would enlighten us with his opinion ).
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But photosynthesis is the business of
CO2 + H2O → C6H12O6 + O2
which is followed by all the processes of life, including the formation of carbonate skeletons. The CO2 in sea or river water arrived by precipitation or direct absorption from the atmosphere.
This all makes sense because there is no other planet with free oxygen in the atmosphere, but there's plenty of CO2 around. Any free oxygen would be rapidly involved in further reactions, so what we have is the result of continuous replenishment by photosynthesis, and the carbon has to go somewhere!
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Ok Alan, one more try: the OP was enquiring where all the carbon in reduced form from the co2 originally in the atmosphere had gone. Photosynthesis releases oxygen and ties up the carbon in various forms and there will be one molecule of oxygen produced for every carbon atom and the carbon atoms may or may not go on to form fossil fuels but the co2 in carbonate has not been reduced. Therefore it does not count as carbon storage, post photosynthesis.
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The OP made the error of assuming that all the carbon extracted from the atmosphere by photosynthesis ended up as oil or coal, so there should be enough fossil fuel to use up all the oxygen in the atmosphere if we burn it. But we know that
Chalk and limestone deposits account for a huge amount of carbon that was absorbed after the carboniferous period by photosynthetic plants and bacteria then eaten by animals and incorporated into their shells or skeletons as CaCO3 and can't be used as fuel.
Some recently-acquired CO2 ends up as vegetable humus or bits of dead animals, and soil depth generally increases at about 1 mm per 100 years if undisturbed.
Living plants continue to exhale oxygen
If the atmospheric content of CO2 increases, plants grow faster and release more oxygen
So the probability is that even if there was enough flammable organic material to consume all the oxygen and it was all burned at once, plant life would gradually replace the oxygen anyway, until there were enough animals to consume the oxygen and produce some temporary dynamic equilibrium, such as has been around for about a billion years.
Not sure what you mean by "reduced", or "storage". Carbon that was extracted from the atmosphere and is no longer part of the plant/animal exhalation cycle is, to my mind, "stored". Apart from coal and oil, there is very little
reduced CO2, i.e. from CO2 + 2 H2O → CH4 + 2O2 or CO2 + 2H2 → C + 2H2O, in nature.
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Lets look at it another way.
By burning fossil fuels we have added about 100 ppm of CO2 to the air.
In doing that we have removed something like 100 ppm of O2
(the actual amount depends on how much hydrogen was in the fuel).
We are talking about "peak oil" and such- and whether or not we have used up all the fossil fuels.
Let's assume that we are actually nowhere near that and we have actually used just 1% of it.
And then let's imagine that - regardless of any possible climate change- we decide to extract and burn all that fuel.
We burn the other 99%
If the 1% we have used raised the CO2 concentration by 100 ppm then the remaining 99% will raise it 99 times as much
We will increase the CO2 by something like 9900 ppm i.e. about 0.99%
And we would reduce the oxygen concentration by about 0.99% from about 21% to about 20%
Now, you can play with chalk until the cows come home, but you won't make a difference to the oxygen that is left.
Where did this excess oxygen come from?
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Not sure what you mean by "reduced",
A change in oxidation state from nominally (IV) to (0)
Converting CO2 to C is a reduction.
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My point precisely. Carbon has not been directly sequestered from the atmosphere as an element.
Wikipedia has an interesting paradox: some of the reduced carbon actually resulted from high atmospheric oxygen levels that supported extensive forest fires leaving charcoal residues.
There is some volcanic graphite and occasional diamonds, but most geological carbon is found as carbonates.
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Carbon has not been directly sequestered from the atmosphere as an element.
It has; we call it coal.
But feel free to answer what I think was the OP's original question.
Where did this excess oxygen come from?
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Coal was not directly sequestered as elemental carbon, but is the result of photosynthesis of atmospheric CO2 to carbohydrates and suchlike (trees) followed millions of years later by pyrolysis and hydrolysis.
The concept of "excess" oxygen is either meaningless or temporarily inevitable. In cosmic terms, all the free atmospheric O2 is "excessive" as it is highly reactive and absent from every other planet. It is (as the OP said) entirely the waste product of photosynthesis, which AFAIK has not been observed elsewhere (though it might have happened briefly on Mars). Therefore you could classify it as entirely "excess" or entirely the intermediate constituent of a series of reactions that has not reached equilibrium.
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Coal was not directly sequestered as elemental carbon, but is the result of photosynthesis of atmospheric CO2 to carbohydrates and suchlike (trees) followed millions of years later by pyrolysis and hydrolysis.
Can you point out the post where you think anyone said otherwise?
In cosmic terms,
Can you point out the post which you think implies that we are talking about anywhere except the planet earth?
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I think the question is "Why is there more oxygen on earth than can be explained by the conversion of CO2 into "C" and O2, based on how much "C" we apparently have?"
(Some of the "C" is coal, some is oil, some cellulose or methane - whatever).
We know that photosynthesis did it.
But where did it put the electrons?
Making oxides into oxygen involves taking the electrons off the oxide ions.
Biology commonly addresses this by sticking them onto (formally) C4+ ions and making C(0) (Actually, it generally goes the whole hog and converts them to (formal) C4- ions, but that's beside the point).
It can also do it by sticking them onto H+ ions and making H2
If that happened on a large scale and the H2 got into the atmosphere and escaped (because it's too light for gravity to trap it) then that would explain the surplus of O2 that we now see.
A huge stock of undiscovered oil-shale or some such might also explain it.
I really don't know what the answer is.
At the moment I'm just wondering if Alan understood the question.
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Quote from: alancalverd on Today at 11:49:30
Coal was not directly sequestered as elemental carbon, but is the result of photosynthesis of atmospheric CO2 to carbohydrates and suchlike (trees) followed millions of years later by pyrolysis and hydrolysis.
Can you point out the post where you think anyone said otherwise?
er, yes:
Quote from: alancalverd on Today at 09:22:19
Carbon has not been directly sequestered from the atmosphere as an element.
It has; we call it coal.
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I think the question is "Why is there more oxygen on earth than can be explained by the conversion of CO2 into "C" and O2, based on how much "C" we apparently have?"
And it has been partially answered, I think, by reference to sedimentary carbonate rocks and soil. One thing we have all ignored is the quantity of "live carbon" in the form of existing plant and animal material - literally the elephant in the room!
There are a few biochemical reactions that release hydrogen and methane (particularly in the animal gut) but the key processes of photosynthesis incorporate it into the -CH2- skeleton of carbohydrates and other complex molecules. See reply #7 above.
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Can you point out the post which you think implies that we are talking about anywhere except the planet earth?
It's important to realise that this planet appears to be unique in its chemical complexity and surface history. Hence we need to consider a large number of processes that have led to the capture of CO2 and the release of O2 over geological time.
If there is a god, its name is the hydrogen bond.
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And it has been partially answered, I think, by reference to sedimentary carbonate rocks
I thought I had explained why they are irrelevant.
Now, you can play with chalk until the cows come home, but you won't make a difference to the oxygen that is left.
One thing we have all ignored is the quantity of "live carbon" in the form of existing plant and animal material - literally the elephant in the room!
Yes, I'm ignoring it.
Here's why
https://bigthink.com/13-8/earth-biomass-distribution/#:~:text=Combined%2C%20all%20life%20on%20Earth,alone%20is%20about%20161%20gigatons.
The earth's biomass is about 550 billion tons.
And much of that mass is water.
Humans (which will do as an example) are about 18% carbon.
So the biomass holds somewhere in the ballpark of 100 billion tons of carbon.
And we know the world's estimated coal reserves are 1,139,471,430,000 tons
Just the coal (never mind lignite, shale, oil, gas etc) has about 10 times as much carbon as all the biology.
So, the reason we ignore the elephant is that its a rather small elephant.
The real question then is, "why didn't you know that?"
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but the key processes of photosynthesis incorporate it into the -CH2- skeleton of carbohydrates and other complex molecules.
We know.
And the reaction is (roughly- assuming it makes glucose)
6 CO2 + 6 H2O -- > C6H12O6 + 6 O2
And if that cellulose burns or metabolised for energy, you get back to where you started. So we can ignore that.
But one potential fate of the glucose it to become coal.
C6H12O6 --> 6C + 6 H2O
So, for every C atom in coal there should be exactly 1 O2 molecule produced.
It's slightly more complex when you consider the hydrogens, but it's not an "order of magnitude" thing.*
Every atom of carbon reduced from CO2 generates a molecule of O2.
There should be an almost exactly 1 to 1 correspondence between reduced carbon atoms and oxygen molecules.
So you should be able to write that the other way round.
There should be exactly 1 carbon atom in "fuel" for every O2 molecule in the atmosphere.
But, in fact, there seem to be a lot more.
Where did they come from?
Or, equivalently, where did the carbon go?
Where do you think the carbon went?
It's not been made into coal or oil.
It's not been made into imaginary elephants either.
So where is it?
* Conceptually, I can ferment the glucose to alcohol, dehydrate it to ethylene and oligomerise / crack the ethylene to any length carbon chain I like (with either a double bond or a ring).
None of those reactions involve O2 so making "oil" does not change the fundamental 1 carbon atom per oxygen molecule ratio.
Faffing about with amines and thiols etc slightly complicates things.
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It's important to realise that this planet appears to be unique
Which is another good reason for ignoring the rest of the cosmos when talking about Earth, isn't it?
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At the moment I'm just wondering if Alan understood the question.
I'm no longer wondering...
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So you should be able to write that the other way round.
There should be exactly 1 carbon atom in "fuel" for every O2 molecule in the atmosphere.
Or in chalk, limestone, extant biomass, coral, soil, or the sludge at the bottom of the sea. Coal and oil production were relatively short phases in geological time and over relatively small areas, compared with all photosynthesis and sedimentation of carbonates.
So the OP's suggestion that there should be enough oil & fossil fuel to use up all the oxygen
is indeed ignoring the weight of the elephant - most of the oxygen was exhaled by organisms that didn't turn into useable fuel.
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It's important to realise that this planet appears to be unique
Which is another good reason for ignoring the rest of the cosmos when talking about Earth, isn't it?
On the contrary. A lot of science is about examining anomalies. And the anomaly of this planet is liquid water on the surface, leading to biochemstry, which modifies the atmosphere.
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Or in chalk, limestone
Why do you keep pretending that calcium carbonate is relevant?
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most of the oxygen was exhaled by organisms that didn't turn into useable fuel.
OK, what happened to those organisms?
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They turned into carbonate rocks, and continue to do so.
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They turned into carbonate rocks, and continue to do so.
And how much oxygen did they add or remove in doing so?
Because that's the way in which they would be relevant to a question about " where did the oxygen come from?".
Did you look at the OP?
It doesn't even mention CO2- it doesn't need to.
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Have you actually read the OP? Do you think photosynthesis doesn't involve CO2? Or are you a troll impersonating my good and learned friend BC?
When I was very young and impressionable, we were taught that the carbonate is one of the less soluble salts of calcium - and indeed of many metals - so tends to form the skeletons of various species of plankton and corals which eventually turn up as sedimentary rock.
It's interesting that the carboniferous period was actually quite a small part of geological history, between much longer periods during which most of the sedimentary rocks of biological origin were formed: whilst trees are currently the most obvious photosynthesisers, it seems that a lot more CO2 was removed from the atmosphere before they evolved.
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Carbonate represents carbon in it's fully oxidised state which has never given up it's oxygen in the process of photosynthesis as opposed to coal, oil, cellulose etc.
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Have you actually read the OP?
I was thinking of asking you the same question
But- what would be the point?
You failed to answer this one.
Quote from: alancalverd on Today at 12:53:57
They turned into carbonate rocks, and continue to do so.
And how much oxygen did they add or remove in doing so?
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They turned into carbonate rocks, and continue to do so.
To turn a plant into carbonate is a very simple process- you just burn it. (Or you can do more complicated things; like feeding animals with it and having them exhale the CO2).
That removes from the atmosphere the oxygen which was released by the plant during its growth.
So, as the OP points out
there should be enough oil & fossil fuel to use up all the oxygen and there doesn't seem to be anywhere near enough to do this.
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Now read the second paragraph of reply #30.
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Now read the second paragraph of reply #30.
It's no more relevant than when I first read it.
Now answer the question...
And how much oxygen did they add or remove in doing so?
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You can imagine some extra-terrestrials turning up on earth with a plan to invade, but being thwarted by out oxygen rich atmosphere.
And you can imagine their equivalent of Alan saying "I have a cunning plan!".
"We can mine lots of olivine, crush it to powder and pump the air through it. That will convert the CO2 to carbonate."
And one can imagine the other aliens saying "What the hell for? The issue isn't CO2, it's oxygen!".
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Quote from: Bored chemist on Yesterday at 22:01:22
And how much oxygen did they add or remove in doing so?
Mutiply the mass of chalk, coral, limestone and all the current living and deceased matter by an appropriate factor (ask a chemist) to determine how much carbon has been extracted form the atmosphere since the dawn of creation. Then using
6 CO2 + 6 H2O -- > C6H12O6 + 6 O2 or whatever photosynthetic process you consider appropriate you can estimate how much oxygen has been released. For those inclined to an easier life, the answer is about 1018 kg, according to Wikipedia.
But since the presence of free oxygen in the atmosphere is unique to this planet, and according to BC Earth's uniqueness is irrelevant, there's no point in discussing it.
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Carbon dioxide extracted as carbonate releases no oxygen, that extracted by photosynthesis does release oxygen on the basis of one molecule of o2 for every atom of c.
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Let's try again
then there should be enough oil & fossil fuel to use up all the oxygen and there doesn't seem to be anywhere near enough to do this.
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Any chance you could make that a bit bigger, BC, the ould eyes aint what they used to be! PS joking.
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Any chance you could make that a bit bigger, BC, the ould eyes aint what they used to be! PS joking.
Yours are not the eyes I'm targeting...
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The statement in enormously large print is obvious. According to a tax inspector* somewhere
And we know the world's estimated coal reserves are 1,139,471,430,000 tons
so on the basis that C + O2 → CO2 you would need about 3.2 x 1015 kg of oxygen to burn it all. Add about 250,000,000,000 tons of oil,** and you are still a factor of several hundred short of what you'd need to use up all the oxygen.
But the original question was "where did all the oxygen come from?" and so far nobody has challenged the geological consensus answer - photosynthesis.
Which raises the next question - where did all the rest of the primordial atmospheric carbon go? And so far, nobody has suggested a plausible (or indeed any) alternative to extant biomass, soil, sedimentary rock, and seabed sludge.
*nobody else would estimate a hidden and unknowable asset to 10 significant figures
** looks more like a petrologist's estimate
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But the original question was "where did all the oxygen come from?" and so far nobody has challenged the geological consensus answer - photosynthesis.
The fact that it apparently doesn't explain all the oxygen is, in fact, a challenge.
It seems that it's quite a difficult one.
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And so far, nobody has suggested a plausible (or indeed any) alternative to extant biomass
And again, Alan fails reading comprehension/ memory test...
If that happened on a large scale and the H2 got into the atmosphere and escaped (because it's too light for gravity to trap it) then that would explain the surplus of O2 that we now see.
A huge stock of undiscovered oil-shale or some such might also explain it.
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nobody else would estimate a hidden and unknowable asset to 10 significant figures
Nobody did.
They added a number of estimates together.
The estimates themselves are published numbers.
The estimate of the mass is known to that precision, but the mass isn't.
It's a little beside the point which is that it's 2 orders of magnitude or so too high for the glib "photosynthesis did it" response, since photosynthesis shouldn't have produced that much oxygen (or equivalently, should have produced more fuel)..
Have you finally realised why chalk etc is irrelevant?
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Which raises the next question - where did all the rest of the primordial atmospheric carbon go?
And, after just 42 posts, you finally understand the OP.
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And the answer.
Sadly, I'm getting too old to waste any more time explaining basic biology and geology here.
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Sadly, I'm getting too old to waste any more time explaining basic biology and geology here.
The whole point of the thread is that the " basic biology and geology " do not explain the observations, do they?
There's too much oxygen.
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I would reckon a lot of the carbon in reduced form is spread thinly throughout the lithosphere. The deposits of fossil fuels often quoted are those that are economical to extract, at the present time. As deposits are exhausted more difficult to mine sources will become economic, eg the Canadian tar sands. Other deposits such as methane clathrates and humous in the soil could be difficult to estimate, I would think.
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Photosynthesis probably began about 3 x 109 years ago. The Carboniferous (coal and oil formation) period only lasted for about 6 x 107 years - about 2% of the total.
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Photosynthesis probably began about 3 x 109 years ago. The Carboniferous (coal and oil formation) period only lasted for about 6 x 107 years - about 2% of the total.
So?
It's not a scheduling problem.
Where's the carbon?
Where did the O2 come from?
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I refer the hon gent to the answers I gave some days ago - or to any decent geology textbook. Or maybe the oxygen was found under a gooseberry bush, like babies, and the fairies took the carbon away.
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I refer the hon gent to the answers I gave some days ago
The ones where you were wittering on about elephants or the ones where you were wittering about chalk?
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Many things react with oxygen. There is plenty of oxygen on/in earth which is 30% by mass, much more than the atmosphere. Do you mean why is there oxygen in the atmosphere?
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https://en.m.wikipedia.org/wiki/Diatom
ps - i Wonder how Wikipedia is still Free & not a Paid Access Service.
GR8!