<p>This is only a partial answer as it doesn't explain why the excess of O<sub>2</sub> stayed but one thing you have to appreciate is the fact that aerobic respiration appeared almost half a billion years after photosynthesis, so we can't really say that photosynthesis and respiration have always balanced each other.  </p>

<p>Cyanobacteria (and with them photosynthesis) are believed to have appeared somewhen between 3 and 2.5Ga (e. g. <strong><a href="http://www.sciencedirect.com/science/article/pii/S0923250803002018" rel="noreferrer">Altermann &amp; Kazmierczak 2003</a></strong>, <strong><a href="http://www.sciencedirect.com/science/article/pii/S0016703703002096#" rel="noreferrer">Brocks et al. 2003</a></strong>) while Mitochondria (and with them aerobic respiration) are thought to have evolved somewhen between 2 and 1.5Ga (see e. g. <strong><a href="http://www.hedgeslab.org/pubs/156.pdf" rel="noreferrer">Hedges et al. 2004</a></strong>).</p>

<p>There was therefore at least half a billion year during which cyanobacteria were producing O<sub>2</sub> with no one able to breathe it.</p>

CC BY-SA 3.0
2015-02-28T11:33:09.330Z
I guess you mean aerobic respiration appeared after photosynthesis, right? (Respiration in the more general sense occurs in all organisms and I don't think a cell could exist without it, but it makes sense that aerobic respiration wouldn't evolve until there was oxygen around for it to use.) I'd be curious to know (a) what the net reaction(s) looked like for the forms of respiration dominant before the great oxidation, and (b) whether any form of anaerobic respiration contributes to maintaining the $\ce{O2}$ concentration today.
N. Virgo
CC BY-SA 3.0
2015-02-28T11:34:32.120Z
(The latter isn't obvious. Something like methanogenesis will create products that then react with $\ce{O2}$, taking it out of the atmosphere after all. But perhaps there are respiratory pathways, for example with mineral electron acceptors, for which this is not the case.) Anyway +1.
N. Virgo
CC BY-SA 3.0
2015-02-28T11:46:22.160Z
Yes, sorry, i meant aerobic respiration, I'll correct the answer.
plannapus
CC BY-SA 3.0
2015-02-28T08:51:12.100Z
2015-02-28T11:46:40.130Z
2015-02-28T11:46:40.130Z
plannapus
<p>My answer goes a little beyond the evidence -- there isn't much evidence.
<br/>
<br/></p>

<h2>The question</h2>

<p>There's a lot of free oxygen now. This oxygen did not suddenly come from underground or from space. So it used to be attached to something. The question is, what was it attached to, and what happened to what it was attached to?
<br/>
<br/></p>

<h2>Background</h2>

<p>First off, there's every reason to think that bacteria already did oxidative phosporylation before there was any free oxygen. It does not require free oxygen, it requires an electron acceptor. O<sub>2</sub> provides the most energy, but many other reactants provide <em>some</em> energy, and the bacterial kingdom uses a bewildering variety of them. To use a different electron acceptor requires only one different enzyme -- the rest of the pathway can be the same.</p>

<p>So before there was free oxygen, prokaryotes did arbitrage -- they evolved to use the best electron donor/electron acceptor pair they could find under whatever conditions they faced at the moment. And everything they used for that had to be created in a cycle. Anything which they used up that was not replaced, would quickly be gone.</p>

<p>Before there was free oxygen, photosynthesis still got done. Some bacteria used H<sub>2</sub>S as an electron donor, creating S which could later be reduced for energy. Some created H<sub>2</sub>. Some could reduce CO<sub>2</sub> so that they could use the carbon and oxygen to make structures they needed. Some could not, but could still get energy from light. One way to do that was almost the same as oxidative phosphorylation, it used the absorbed light energy for electron transport instead of using redox energy, in practically the same pathway.</p>

<p>Cycles. Every reaction must be undone, or its products will increase to the point that the reaction gets very slow. The exception is products that change state. A solid or gas product won't inhibit the reaction much.</p>

<p>So, a bewildering variety of electron donors and acceptors. Photosynthesis creates energetic pairs of molecules or ions. Then redox creates less-energetic pairs of molecules or ions.</p>

<p>What was it that was bound to oxygen in the old days, that was not bound later?
<br/>
<br/></p>

<h2>Some possibilities</h2>

<ol>
<li><p>Hydrogen. One form of photosynthesis creates H<sub>2</sub>. Maybe, at some times a whole lot of H<sub>2</sub> was created which was lost to space. Just as much O and less H leaves room for O<sub>2</sub> left over.</p></li>
<li><p>Sulfur. Maybe most of the sulfur in the oceans was stored as SO<sub>3</sub>. </p></li>
</ol>

<p>H<sub>2</sub> SO<sub>3</sub> -> S + H<sub>2</sub>O +  O<sub>2</sub>. </p>

<p>Sulfur can be oxidized -- SO<sub>3</sub>. Or it can replace Oxygen as an oxidizer -- H<sub>2</sub>O -> H<sub>2</sub>S etc.</p>

<p>So by changing states it could affect free O<sub>2</sub>. And solid sulfur could wind up on the ocean bottom where it would be subducted.</p>

<ol start="3">
<li>Heavy metals + sulfur. Maybe there was a lot of iron and nickel etc dissolved in the ancient ocean, along with a lot of sulfur. Iron sulfate is fairly soluble at room temperature, nearly 300 grams/liter. Provided it is not alkaline. But iron sulfide is not soluble. Lots of other heavy metals behave similarly. </li>
</ol>

<p>F<sub>3</sub>O<sub>4</sub> +  4 H<sub>2</sub>SO<sub>3</sub> -> F<sub>3</sub>S<sub>4</sub> + 6 O<sub>2</sub> + 4 H<sub>2</sub>0  (and many other combinations)</p>

<ol start="4">
<li>Nitrogen. Nitrogen can be reduced to NH<sub>4</sub> or oxidized to NO<sub>2</sub> or NO<sub>3</sub>. </li>
</ol>

<p>2 NO<sub>2</sub> + 4 H+ = N<sub>2</sub> + O<sub>2</sub> + 2 H<sub>2</sub>O</p>

<p>Perhaps there was a time when the atmosphere had only 75% as much N<sub>2</sub> as it does now, and no O<sub>2</sub>. This reaction would imply the oceans used to be more acidic than they are now. But there could be other reactions that would counteract that, and there were lots of other buffers.</p>

<ol start="5">
<li>Silicon. Silicon is usually oxidized, SiO<sub>2</sub>. It doesn’t have to have that ratio. Other silicon compounds are possible, eg carborundum SiC, and perryite Fe<sub>5</sub>Si<sub>2</sub> which is stable in acid water, silicon nitride Si<sub>3</sub>N<sub>4</sub>, silicon phosphide SiP<sub>2</sub> etc . Siloxanes can have ratio Si:O of 1:1. Low molecular weight siloxanes are produced by modern anaerobic biogas fermenters, though it could possibly be eukaryotes producing them. There is potentially a tremendous amount of SiO<sub>2</sub> available to release oxygen, although only a little of it is soluble at any one time. </li>
</ol>

<p>Or bacteria could have metabolized silicic acid into insoluble compounds that had less oxygen. This is entirely hypothetical since only a little carborundum has been discovered, and the rest would have had to be subducted. </p>

<p>Banded iron formations do though have layers of amorphous quartz. Silicon dioxide was being removed from the water. Perhaps it was alternately iron being removed while soluble siloxanes accumulated in water, and then the siloxanes were converted to silica and removed while iron accumulated in water.</p>

<p>It was a complicated web of reactions. Photosynthesis provided the energy to create energy-rich chemicals. Meanwhile every organism that was not photosynthetic was busy finding its best mix of catalyzing chemical reactions that provided energy, versus creating the molecules needed to grow and reproduce. Strange things happened.</p>

CC BY-SA 4.0
2018-05-08T06:18:15.240Z
2018-05-13T12:29:10.053Z
2018-05-13T12:29:10.053Z
J Thomas
<p>I will explore the answer admitting that the Earth's temperature in the ancient past was much higher than we now assume as possible. The current standard model is the 'Snowball Earth' which leaves many unsolved problems - see 'Faint Young Sun Paradox'.  </p>

<p>I will assume that the total amount of $\ce{H_2O}$, $\ce{CO_2}$, $\ce{O_2}$ is substantially constant throughout the entire history of the earth.</p>

<p>All the water of the oceans would stay in the atmosphere layer   provided the temperature was high enough. The percentage of oxygen would be $\approx 0$ because it would be masked by the massive presence of $\ce{H_2O}$.  </p>

<p>Later, when the temperature dropped, the water has migrated to the ocean floor and the percentage of $\ce{O}$ exploded to current levels. This fact is called the 'Great Oxygenation Event' and it is not very well understood under the standard model. </p>

<p>About the <strong>free Oxygen origin</strong>: (Copy / Paste)  </p>

<blockquote>
  <p>"There are two known natural ways of producing oxygen: by UV
  dissociation of H2O and by photosynthesis. In the ECM, the former
  process was initially much more efficient than at present because of
  the huge amount of water vapour and of the greater intensity of UV
  radiation occurring then. The biological production of oxygen would
  have been important during the Archean, which ended at
  2.5 Ga, therefore earlier than the GOE. The usual approach is to consider that the biologically produced oxygen was first combined with
  dissolved iron in oceans and only significantly released to the
  atmosphere later – a way to explain the delay between the presumed
  time of the biological production of oxygen and the rise of its
  atmospheric level. Here, there is no need to consider a delay – the
  biologically produced oxygen was dissolved in water and absorbed by
  the huge atmosphere without significantly changing its composition;
  the oxygen level increased only when the atmosphere significantly
  decreased due to the condensation of water vapour. One can now
  consider that oxygen was produced in large amounts since the
  beginning, first from UV dissociation, at a rate that decreased over
  time, and very soon followed by biological production. In this case,
  there was an important amount of free oxygen in the atmosphere long
  before its atmospheric level started to increase significantly; and
  some potential evidences of it can be identified (for a review see
  Yamaguchi, 2005)."</p>
</blockquote>

<p><strong>ECM</strong> stands for <strong>Evolving Climate Model</strong> where this new concept was brought to life in a formal document (if you wish to explore further you can follow the 2nd link in my profile, not peer-reviewed)  </p>

<p>EDIT add:<br>
Although no one wants to peer review the document of ECM,(*) its graph on fig.9 provides modeled data that is aligned with the most recent measurement of Oxigen.<br>
Measures goes against all of the accepted models ( 5 times more Oxigen at 815Ma), as seen on fig 4 on this news<br>
<a href="https://i.sstatic.net/P0MPn.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/P0MPn.jpg" alt="enter image description here"></a><a href="http://motherboard.vice.com/en_uk/read/scientists-release-air-that-has-been-trapped-for-800-million-years" rel="nofollow noreferrer">http://motherboard.vice.com/en_uk/read/scientists-release-air-that-has-been-trapped-for-800-million-years</a></p>

<p>On the contrary the Fig. 9 of ECM  <a href="https://i.sstatic.net/xt8uK.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/xt8uK.png" alt="enter image description here"></a>
Fig. 9. The variation of Oxygen volumetric ratio in the ECM1 due
to the variation of the size of the atmosphere, holding the
amount of Oxygen constant (thick blue line). The grey lines
represent the limits for the oxygen volumetric ratio (partial
pressure in the atmosphere) estimated in Holland (2006)  </p>

<p>ECM is not peer-reviewed but it predicted the data to be seen (it is Data-reviewed) !   </p>

<p>(*) ECM is a creation of an engineer, and scientists assume that science is not for engineers.  </p>

<p>note: This new measurement enable to say: Oxygen first, Life second, rendering erroneous most of the answers one can find around.   </p>

<p>Why so many down votes (5) if it is notorious that none could find an error in the document?  </p>

CC BY-SA 3.0
2015-02-28T04:05:15.210Z
2016-08-25T11:21:52.243Z
2016-08-25T11:21:52.243Z
Helder Velez
<p>Because of photosynthesis, obviously.  But then it's not actually that obvious after all, because photosynthesis is mostly balanced by respiration. </p>

<p>We can summarise the processes of photosynthesis and respiration like this:
$$\begin{align}
\ce{CO2 + H2O + h\nu} &amp; \rightarrow \ce{O2 + CH2O(biomass)} \\
\ce{O2 + CH2O(biomass)} &amp; \rightarrow \ce{CO2 + H2O}
\end{align}
$$
If these two reactions were always balanced then the concentration of $\ce{O2}$ would never have changed. If I understand correctly, there are abiotic processes that deplete $\ce{O2}$ to form iron oxides, and so in order for there to be persistent $\ce{O2}$ in the Earth's atmosphere, the biosphere as a whole must continually produce an excess of it. In order for this to happen, there must be some processes that consume biomass at a non-neglible rate without removing a corresponding amount of $\ce{O2}$ from the atmosphere.</p>

<p>My question is, what are the processes primarily responsible for this? Is it just due to the burial of unoxidised organic matter (to form coal, oil, etc.), or is there more to it than that?</p>

<p>If they are different processes, I'm interested both in what caused the excess of oxygen during the "great oxidation" event, and what maintains the excess of oxygen on the modern Earth.</p>

CC BY-SA 3.0
2015-02-21T15:19:43.343Z
I am no biologist, but photosynthesis is not necessarily used to produce sugars.  Chlorophyll absorbs photons of light and (in conjunction with other proteins) splits water into O2 and H+, which is what produces the O2 in the atmosphere, but the electron flow can also be used to generate ATP, which is the cells basic energy source.  So photosynthesis can support celluar activity without producing sugars or respiration.  The basic point is that production of sugars for respiration is one use of phyotosynthesis, there are others that still produce O2 as a by product (e.g. in stromatelites).
Dikran Marsupial
CC BY-SA 3.0
2015-02-22T00:42:26.513Z
@DikranMarsupial can you write down a net reaction and/or reference (or just a suitable search term) for the metabolic pathways  you mention that produce $\ce{O2}$ without fixing carbon? What happens to the H?
N. Virgo
CC BY-SA 3.0
2015-02-22T16:16:46.773Z
no, as I said, I am not a biologist, I just did a bit of reading on Wikipedia and elsewhere.  The breaking up of water is what produces the O2, and that produces ATP and NADPH (which is the reducing agent for carbon fixing), so you would need to look for other uses of these molecules in the cellular machinery.
Dikran Marsupial
CC BY-SA 3.0
2015-02-22T16:22:57.607Z
BTW it looks like nitrogen fixing might be another use of NADPH, http://en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleotide_phosphate, which is something cyanobacteria are noted for http://en.wikipedia.org/wiki/Cyanobacteria#Nitrogen_fixation.  However, as I said, the details are beyond me.
Dikran Marsupial
CC BY-SA 3.0
2015-02-23T14:03:41.017Z
This paper http://rstb.royalsocietypublishing.org/content/361/1470/903 suggest that it was burial of unoxidised organic matter that was responsible.
Dikran Marsupial
CC BY-SA 3.0
2015-03-02T11:34:27.353Z
Actually, now I am curious about what would have caused it to _stay_ imbalanced. Logically, if it is a reversible process, then it could go to the point of having enough that a boom of consumers appears, leading to an oxygen crash.

Any idea why this would not have happened, or is this worth asking as a separate question?
mtb-za
CC BY-SA 3.0
2015-03-02T12:41:40.523Z
@mtb-za based on the comments and answers so far, I *think* it's because biomass gets buried in anoxic conditions to form stuff like peat, some of which then eventually gets buried and fossilised into coal and oil, which consumers can't oxidise because it's physically separated from the oxygen in the atmosphere. (I'm fairly sure this is the right story, but I'm holding out for an answer from an expert who can explain it all in detail.)
N. Virgo
<atmosphere><geochemistry><biogeochemistry><geobiology><great-oxidation-event>
Why does Earth have abundant oxygen in the atmosphere?
N. Virgo
# Why does Earth have abundant oxygen in the atmosphere?

(Asked by: username_0 on 2015-02-19)

Because of photosynthesis, obviously. But then it's not actually that obvious after all, because photosynthesis is mostly balanced by respiration.

We can summarise the processes of photosynthesis and respiration like this:
$$\begin{align}
\ce{CO2 + H2O + h\nu} & \rightarrow \ce{O2 + CH2O(biomass)} \\
\ce{O2 + CH2O(biomass)} & \rightarrow \ce{CO2 + H2O}
\end{align}
$$
If these two reactions were always balanced then the concentration of $\ce{O2}$ would never have changed. If I understand correctly, there are abiotic processes that deplete $\ce{O2}$ to form iron oxides, and so in order for there to be persistent $\ce{O2}$ in the Earth's atmosphere, the biosphere as a whole must continually produce an excess of it. In order for this to happen, there must be some processes that consume biomass at a non-neglible rate without removing a corresponding amount of $\ce{O2}$ from the atmosphere.

My question is, what are the processes primarily responsible for this? Is it just due to the burial of unoxidised organic matter (to form coal, oil, etc.), or is there more to it than that?

If they are different processes, I'm interested both in what caused the excess of oxygen during the "great oxidation" event, and what maintains the excess of oxygen on the modern Earth.

**Tags:** atmosphere, geochemistry, biogeochemistry, geobiology, great-oxidation-event

> **Comments:**
> **username_1**: I am no biologist, but photosynthesis is not necessarily used to produce sugars.  Chlorophyll absorbs photons of light and (in conjunction with other proteins) splits water into O2 and H+, which is what produces the O2 in the atmosphere, but the electron flow can also be used to generate ATP, which is the cells basic energy source.  So photosynthesis can support celluar activity without producing sugars or respiration.  The basic point is that production of sugars for respiration is one use of phyotosynthesis, there are others that still produce O2 as a by product (e.g. in stromatelites).  
> **username_0**: @username_1 can you write down a net reaction and/or reference (or just a suitable search term) for the metabolic pathways  you mention that produce $\ce{O2}$ without fixing carbon? What happens to the H?  
> **username_1**: no, as I said, I am not a biologist, I just did a bit of reading on Wikipedia and elsewhere.  The breaking up of water is what produces the O2, and that produces ATP and NADPH (which is the reducing agent for carbon fixing), so you would need to look for other uses of these molecules in the cellular machinery.  
> **username_1**: BTW it looks like nitrogen fixing might be another use of NADPH, http://en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleotide_phosphate, which is something cyanobacteria are noted for http://en.wikipedia.org/wiki/Cyanobacteria#Nitrogen_fixation.  However, as I said, the details are beyond me.  
> **username_1**: This paper http://rstb.royalsocietypublishing.org/content/361/1470/903 suggest that it was burial of unoxidised organic matter that was responsible.  
> **username_2**: Actually, now I am curious about what would have caused it to _stay_ imbalanced. Logically, if it is a reversible process, then it could go to the point of having enough that a boom of consumers appears, leading to an oxygen crash.  Any idea why this would not have happened, or is this worth asking as a separate question?  
> **username_0**: @username_2 based on the comments and answers so far, I *think* it's because biomass gets buried in anoxic conditions to form stuff like peat, some of which then eventually gets buried and fossilised into coal and oil, which consumers can't oxidise because it's physically separated from the oxygen in the atmosphere. (I'm fairly sure this is the right story, but I'm holding out for an answer from an expert who can explain it all in detail.)  

---

## 3 answers

### Answer by username_3 on 2015-02-28. Score: 9

This is only a partial answer as it doesn't explain why the excess of O2 stayed but one thing you have to appreciate is the fact that aerobic respiration appeared almost half a billion years after photosynthesis, so we can't really say that photosynthesis and respiration have always balanced each other.

Cyanobacteria (and with them photosynthesis) are believed to have appeared somewhen between 3 and 2.5Ga (e. g. **[Altermann & Kazmierczak 2003](http://www.sciencedirect.com/science/article/pii/S0923250803002018)**, **[Brocks et al. 2003](http://www.sciencedirect.com/science/article/pii/S0016703703002096#)**) while Mitochondria (and with them aerobic respiration) are thought to have evolved somewhen between 2 and 1.5Ga (see e. g. **[Hedges et al. 2004](http://www.hedgeslab.org/pubs/156.pdf)**).

There was therefore at least half a billion year during which cyanobacteria were producing O2 with no one able to breathe it.

> **Comments:**
> **username_0**: I guess you mean aerobic respiration appeared after photosynthesis, right? (Respiration in the more general sense occurs in all organisms and I don't think a cell could exist without it, but it makes sense that aerobic respiration wouldn't evolve until there was oxygen around for it to use.) I'd be curious to know (a) what the net reaction(s) looked like for the forms of respiration dominant before the great oxidation, and (b) whether any form of anaerobic respiration contributes to maintaining the $\ce{O2}$ concentration today.  
> **username_0**: (The latter isn't obvious. Something like methanogenesis will create products that then react with $\ce{O2}$, taking it out of the atmosphere after all. But perhaps there are respiratory pathways, for example with mineral electron acceptors, for which this is not the case.) Anyway +1.  
> **username_3**: Yes, sorry, i meant aerobic respiration, I'll correct the answer.  

---

### Answer by username_4 on 2018-05-08. Score: 2

My answer goes a little beyond the evidence -- there isn't much evidence.

## The question

There's a lot of free oxygen now. This oxygen did not suddenly come from underground or from space. So it used to be attached to something. The question is, what was it attached to, and what happened to what it was attached to?

## Background

First off, there's every reason to think that bacteria already did oxidative phosporylation before there was any free oxygen. It does not require free oxygen, it requires an electron acceptor. O2 provides the most energy, but many other reactants provide *some* energy, and the bacterial kingdom uses a bewildering variety of them. To use a different electron acceptor requires only one different enzyme -- the rest of the pathway can be the same.

So before there was free oxygen, prokaryotes did arbitrage -- they evolved to use the best electron donor/electron acceptor pair they could find under whatever conditions they faced at the moment. And everything they used for that had to be created in a cycle. Anything which they used up that was not replaced, would quickly be gone.

Before there was free oxygen, photosynthesis still got done. Some bacteria used H2S as an electron donor, creating S which could later be reduced for energy. Some created H2. Some could reduce CO2 so that they could use the carbon and oxygen to make structures they needed. Some could not, but could still get energy from light. One way to do that was almost the same as oxidative phosphorylation, it used the absorbed light energy for electron transport instead of using redox energy, in practically the same pathway.

Cycles. Every reaction must be undone, or its products will increase to the point that the reaction gets very slow. The exception is products that change state. A solid or gas product won't inhibit the reaction much.

So, a bewildering variety of electron donors and acceptors. Photosynthesis creates energetic pairs of molecules or ions. Then redox creates less-energetic pairs of molecules or ions.

What was it that was bound to oxygen in the old days, that was not bound later?

## Some possibilities

1. Hydrogen. One form of photosynthesis creates H2. Maybe, at some times a whole lot of H2 was created which was lost to space. Just as much O and less H leaves room for O2 left over.
2. Sulfur. Maybe most of the sulfur in the oceans was stored as SO3.

H2 SO3 -> S + H2O + O2.

Sulfur can be oxidized -- SO3. Or it can replace Oxygen as an oxidizer -- H2O -> H2S etc.

So by changing states it could affect free O2. And solid sulfur could wind up on the ocean bottom where it would be subducted.

3. Heavy metals + sulfur. Maybe there was a lot of iron and nickel etc dissolved in the ancient ocean, along with a lot of sulfur. Iron sulfate is fairly soluble at room temperature, nearly 300 grams/liter. Provided it is not alkaline. But iron sulfide is not soluble. Lots of other heavy metals behave similarly.

F3O4 + 4 H2SO3 -> F3S4 + 6 O2 + 4 H20 (and many other combinations)

4. Nitrogen. Nitrogen can be reduced to NH4 or oxidized to NO2 or NO3.

2 NO2 + 4 H+ = N2 + O2 + 2 H2O

Perhaps there was a time when the atmosphere had only 75% as much N2 as it does now, and no O2. This reaction would imply the oceans used to be more acidic than they are now. But there could be other reactions that would counteract that, and there were lots of other buffers.

5. Silicon. Silicon is usually oxidized, SiO2. It doesn’t have to have that ratio. Other silicon compounds are possible, eg carborundum SiC, and perryite Fe5Si2 which is stable in acid water, silicon nitride Si3N4, silicon phosphide SiP2 etc . Siloxanes can have ratio Si:O of 1:1. Low molecular weight siloxanes are produced by modern anaerobic biogas fermenters, though it could possibly be eukaryotes producing them. There is potentially a tremendous amount of SiO2 available to release oxygen, although only a little of it is soluble at any one time.

Or bacteria could have metabolized silicic acid into insoluble compounds that had less oxygen. This is entirely hypothetical since only a little carborundum has been discovered, and the rest would have had to be subducted.

Banded iron formations do though have layers of amorphous quartz. Silicon dioxide was being removed from the water. Perhaps it was alternately iron being removed while soluble siloxanes accumulated in water, and then the siloxanes were converted to silica and removed while iron accumulated in water.

It was a complicated web of reactions. Photosynthesis provided the energy to create energy-rich chemicals. Meanwhile every organism that was not photosynthetic was busy finding its best mix of catalyzing chemical reactions that provided energy, versus creating the molecules needed to grow and reproduce. Strange things happened.


---

### Answer by username_5 on 2015-02-28. Score: -6

I will explore the answer admitting that the Earth's temperature in the ancient past was much higher than we now assume as possible. The current standard model is the 'Snowball Earth' which leaves many unsolved problems - see 'Faint Young Sun Paradox'.

I will assume that the total amount of $\ce{H\_2O}$, $\ce{CO\_2}$, $\ce{O\_2}$ is substantially constant throughout the entire history of the earth.

All the water of the oceans would stay in the atmosphere layer provided the temperature was high enough. The percentage of oxygen would be $\approx 0$ because it would be masked by the massive presence of $\ce{H\_2O}$.

Later, when the temperature dropped, the water has migrated to the ocean floor and the percentage of $\ce{O}$ exploded to current levels. This fact is called the 'Great Oxygenation Event' and it is not very well understood under the standard model.

About the **free Oxygen origin**: (Copy / Paste)

> "There are two known natural ways of producing oxygen: by UV
> dissociation of H2O and by photosynthesis. In the ECM, the former
> process was initially much more efficient than at present because of
> the huge amount of water vapour and of the greater intensity of UV
> radiation occurring then. The biological production of oxygen would
> have been important during the Archean, which ended at
> 2.5 Ga, therefore earlier than the GOE. The usual approach is to consider that the biologically produced oxygen was first combined with
> dissolved iron in oceans and only significantly released to the
> atmosphere later – a way to explain the delay between the presumed
> time of the biological production of oxygen and the rise of its
> atmospheric level. Here, there is no need to consider a delay – the
> biologically produced oxygen was dissolved in water and absorbed by
> the huge atmosphere without significantly changing its composition;
> the oxygen level increased only when the atmosphere significantly
> decreased due to the condensation of water vapour. One can now
> consider that oxygen was produced in large amounts since the
> beginning, first from UV dissociation, at a rate that decreased over
> time, and very soon followed by biological production. In this case,
> there was an important amount of free oxygen in the atmosphere long
> before its atmospheric level started to increase significantly; and
> some potential evidences of it can be identified (for a review see
> Yamaguchi, 2005)."

**ECM** stands for **Evolving Climate Model** where this new concept was brought to life in a formal document (if you wish to explore further you can follow the 2nd link in my profile, not peer-reviewed)

EDIT add:  
Although no one wants to peer review the document of ECM,(\*) its graph on fig.9 provides modeled data that is aligned with the most recent measurement of Oxigen.  
Measures goes against all of the accepted models ( 5 times more Oxigen at 815Ma), as seen on fig 4 on this news  
[![enter image description here](https://i.sstatic.net/P0MPn.jpg)](https://i.sstatic.net/P0MPn.jpg)<http://motherboard.vice.com/en_uk/read/scientists-release-air-that-has-been-trapped-for-800-million-years>

On the contrary the Fig. 9 of ECM [![enter image description here](https://i.sstatic.net/xt8uK.png)](https://i.sstatic.net/xt8uK.png)
Fig. 9. The variation of Oxygen volumetric ratio in the ECM1 due
to the variation of the size of the atmosphere, holding the
amount of Oxygen constant (thick blue line). The grey lines
represent the limits for the oxygen volumetric ratio (partial
pressure in the atmosphere) estimated in Holland (2006)

ECM is not peer-reviewed but it predicted the data to be seen (it is Data-reviewed) !

(\*) ECM is a creation of an engineer, and scientists assume that science is not for engineers.

note: This new measurement enable to say: Oxygen first, Life second, rendering erroneous most of the answers one can find around.

Why so many down votes (5) if it is notorious that none could find an error in the document?


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