Evidence record

Why is there so much oxygen?

Every sentence on the exploration belongs to at least one claim below. Each says what kind of statement it is, what it rests on, what the evidence does not establish, and how far it was checked. Nothing here is a score, and none of it is a verdict on a belief or a theory.

Last checked 24 September 2026.

Source checked: 43
A judgement, not a fact: 5
Presented as open: 4
Partly checked: 2

If something here is wrong, misquoted, out of date or unfair, write to support@unknownoceans.com and give the claim number, which does not change.

What the question takes for granted

A question about a balance rather than an event: oxygen persists only while it is replaced, so the page asks why the replacement began when it did, why it stepped up twice, and what holds the level now. Each of those is still argued.

There is a lot of oxygen, and it does not keep itself
Established
Oxygen is a fifth of the air, and over geological time it is taken back by oxidation of buried carbon and pyrite and by reduced volcanic gases, so a large standing amount needs a source.
The level is steady enough now to need explaining
Established
Since about 420 million years ago oxygen has stayed within a bounded range, which the literature treats as a puzzle; the upper bound is less certain than the charcoal floor.
The history came in two clean steps
Contested
The two-step outline is what the Lyons review calls the classical view; it and later work describe a rise, overshoot and fall after the first step, brief returns to low oxygen, and a second rise that ran into the Devonian.

How the question is labelled

Claim: The waste product

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: Oxygen

Kind: Framing. Signposting. It asserts nothing a source could check.

The question

Claim: A fifth of the air is a reactive gas

Kind: Present-day figure. A count, survey or report finding, as the named source gives it.
Review: Source checked. The cited passage was read, and it says this.

"Reactive" is the page’s word; the Mills review describes the oxygen being taken back by oxidation of buried carbon and pyrite in rocks.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, opening paragraph
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: it makes up 21% of the modern atmosphere
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2, What controls O2 levels
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: in the long-term carbon cycle the net O 2 source linked to carbon and pyrite burial is matched by the sinks through oxidation of fossil organic carbon or pyrite sulfur in ancient sediments, either directly during exposure and weathering or through metamorphism

Later work looked for

A present-day composition, stated in both reviews; nothing to revise.

Claim 3 · checked 24 September 2026 · AI-assisted audit

Claim: that should not persist.

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s reading: left without a source, the sinks the Mills review describes would take the oxygen out of the air.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2, What controls O2 levels
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: in the long-term carbon cycle the net O 2 source linked to carbon and pyrite burial is matched by the sinks through oxidation of fossil organic carbon or pyrite sulfur in ancient sediments, either directly during exposure and weathering or through metamorphism

Claim 4 · checked 24 September 2026 · AI-assisted audit

Claim: It persists because it has been replaced as fast as rocks and volcanic gases take it away,

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Over geological time the net source, carbon and pyrite burial, is matched by the sinks, so the level holds; the Vitali paper says the whole atmospheric inventory was replaced more than a hundred times in the last 420 million years.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2, What controls O2 levels
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: in the long-term carbon cycle the net O 2 source linked to carbon and pyrite burial is matched by the sinks through oxidation of fossil organic carbon or pyrite sulfur in ancient sediments, either directly during exposure and weathering or through metamorphism
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, opening paragraphs
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: offset by consumption during reactions with reduced compounds emanating from Earth’s interior (such as reduced forms of hydrogen, carbon, sulphur and iron)
Context
Combined effects of photorespiration and fire strongly regulate atmospheric oxygen levelsIntroduction, first paragraph
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Model
The source reads: despite the whole atmospheric inventory being completely replaced more than 100 times throughout this period

Later work looked for

How the carbon and oxygen cycle works; not a finding later work revises.

Corrected

24 September 2026. Previously: “It is there because something has been making it faster than the rocks can consume it, for well over two billion years.” The Mills review says the long-term source is matched by the sinks, not outrunning them, and the source is burial rather than production; "well over two billion years" ran past the 2.22 billion years Poulton and others give for permanent oxygenation.

Claim 5 · checked 24 September 2026 · AI-assisted audit

Claim: for more than two billion years.

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, opening paragraph
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Evidence for a permanent rise to appreciable concentrations of O2in the atmosphere some time between 2.4 and 2.1 billion years (Gyr) ago
Context
A 200-million-year delay in permanent atmospheric oxygenationabstract
Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record · Measurement
The source reads: we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago ... Oxygen levels thus fluctuated across the threshold of 10-5 of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving ... at about 2.22 billion years ago

What this does not establish

The Poulton paper was read as its abstract only.

Later work looked for

Crossref, 2021 on, "Great Oxidation Event timing sulfur isotopes": Poulton and others (2021) put permanent oxygenation at about 2.22 billion years ago, and Uveges and others (2023) find the later returns of the oxygen-free signal brief; page updated to report both.

Claim 6 · checked 24 September 2026 · AI-assisted audit

Claim: Oxygen accumulated in two great steps separated by nearly two billion years.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmosphereFig. 1 caption
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: The faded red curve shows a ‘classical, two-step’ view of atmospheric evolution
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 310, In the wake of the GOE
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: waited patiently for almost two billion years before it climbed higher
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: We conclude that O 2 probably made up around 5–10% of the atmosphere during the Cambrian and rose in pulses to 15–20% in the Devonian, reaching a further peak of greater than 25% in the Permo-Carboniferous before declining toward the present day.

What this does not establish

Two steps is the classical outline. The Lyons review contrasts it with an emerging model in which oxygen rose, overshot and fell after the first step, and on the Mills curve the second step ran on into the Devonian.

Later work looked for

Crossref, 2023 on, "Phanerozoic atmospheric oxygen": the 2023 review is the latest field-level curve found; Vitali and others (2026) give 15 to 40 per cent since about 420 million years ago, consistent with it.

Claim 7 · checked 24 September 2026 · AI-assisted audit

Claim: What produced it is known.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, The first oxygen from photosynthesis
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Because oxygenic photosynthesis is the only significant source of free oxygen on Earth’s surface
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: the only other way to produce large amounts of molecular oxygen is through biological means: oxygenic photosynthesis

What this does not establish

Known as a process; when oxygen-producing photosynthesis began is not agreed (claim 53).

Later work looked for

Both reviews, 2014 and 2023, agree; nothing found that changes it.

Claim 8 · checked 24 September 2026 · AI-assisted audit

Claim: Why it rose when it did, and why it waited so long between steps, is not.

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 310
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: The reasons for this rise and fall remain unresolved
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313, Another step towards the modern world
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: much remains unknown about the redox structure of the ocean and atmosphere during the later part of the Proterozoic

Claim 9 · checked 24 September 2026 · AI-assisted audit

Claim: Oxygen is corrosive.

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s word for a gas that reacts with reduced material; the Lyons review describes oxygen consumed by reduced gases and ions from Earth’s interior.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, opening paragraphs
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: offset by consumption during reactions with reduced compounds emanating from Earth’s interior (such as reduced forms of hydrogen, carbon, sulphur and iron)

Claim 10 · checked 24 September 2026 · AI-assisted audit

Claim: Left alone with rock and volcanic gas it reacts away,

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, opening paragraphs
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: offset by consumption during reactions with reduced compounds emanating from Earth’s interior (such as reduced forms of hydrogen, carbon, sulphur and iron)
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2, What controls O2 levels
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: in the long-term carbon cycle the net O 2 source linked to carbon and pyrite burial is matched by the sinks through oxidation of fossil organic carbon or pyrite sulfur in ancient sediments, either directly during exposure and weathering or through metamorphism

Later work looked for

How the carbon and oxygen cycle works; not a finding later work revises.

Claim 11 · checked 24 September 2026 · AI-assisted audit

Claim: which is why there was almost none for the first half of Earth’s history.

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, opening paragraph
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: free oxygen, at levels mostly less than 0.001% of those present in the atmosphere today, was anything but plentiful during the first half of Earth’s 4.5-billion-year history

What this does not establish

Why there was so little is itself the question the page goes on to discuss: the Lyons review ties it to buffering sinks, and a minority view says oxygen was not yet being made (claim 49).

Later work looked for

Crossref, 2021 on, "Great Oxidation Event timing": later work moves the permanent rise to about 2.22 billion years ago, still roughly half of Earth’s history.

Corrected

24 September 2026. Previously: “which is what happened for the first billion years and more of Earth’s history.” When oxygen-producing photosynthesis began is not agreed, so "what happened for the first billion years" asserted consumption over a period nobody can show oxygen was being made. The Lyons review carries the scarcity: under 0.001 per cent of today’s level for the first half of Earth’s history.

Claim 12 · checked 24 September 2026 · AI-assisted audit

Claim: That it is here in quantity is a statement about a continuous supply rather than about a one-off event.

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

Follows from the matched source and sinks in the Mills review and the repeated replacement of the inventory the Vitali paper describes.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2, What controls O2 levels
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: in the long-term carbon cycle the net O 2 source linked to carbon and pyrite burial is matched by the sinks through oxidation of fossil organic carbon or pyrite sulfur in ancient sediments, either directly during exposure and weathering or through metamorphism
Context
Combined effects of photorespiration and fire strongly regulate atmospheric oxygen levelsIntroduction, first paragraph
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Model
The source reads: despite the whole atmospheric inventory being completely replaced more than 100 times throughout this period

Corrected

24 September 2026. Previously: “a statement about a continuous imbalance rather than” Over long times the source is matched by the sinks, per the Mills review; the level holds because it is replaced, not because production outruns consumption.

Claim 13 · checked 24 September 2026 · AI-assisted audit

How it got here

Claim: How it got here

Kind: Framing. Signposting. It asserts nothing a source could check.

It came from photosynthesis, and it came late

Claim: It came from photosynthesis, and it came late

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, The first oxygen from photosynthesis
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Because oxygenic photosynthesis is the only significant source of free oxygen on Earth’s surface
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, opening paragraph
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: free oxygen, at levels mostly less than 0.001% of those present in the atmosphere today, was anything but plentiful during the first half of Earth’s 4.5-billion-year history

Later work looked for

Both reviews, 2014 and 2023, agree; nothing found that changes it.

Claim 15 · checked 24 September 2026 · AI-assisted audit

Claim: Oxygen-producing photosynthesis evolved in cyanobacteria,

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 308
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Cyanobacteria are important because they were the earliest important producers of O2by photosynthesis

Later work looked for

Crossref, 2021 on: nothing read that changes the attribution; the timing remains disputed (claim 53).

Claim 16 · checked 24 September 2026 · AI-assisted audit

Claim: and the isotopic evidence puts the rise in atmospheric oxygen between about 2.4 and 2.3 billion years ago, the Great Oxidation Event.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: the disappearance of distinctive non-mass-dependent (NMD) sulphur isotope fractionations in sedimentary rocks deposited after about 2.4–2.3 Gyr ago
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313 to 314, closing summary
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: The presumed disappearance of NMD sulphur isotope signals narrowed that window to between 2.4 and 2.3 Gyr ago
Context
A 200-million-year delay in permanent atmospheric oxygenationabstract
Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record · Measurement
The source reads: with the initial rise of oxygen concentration to above 10-5 of the present atmospheric level constrained to about 2.43 billion years ago

What this does not establish

The loss of the sulphur signal dates the rise; Poulton and others argue oxygen did not stay up until about 2.22 billion years ago (claim 40).

Later work looked for

Corrected

24 September 2026. Previously: “the isotopic evidence puts the permanent rise in atmospheric oxygen between” The Lyons review puts the permanent rise between 2.4 and 2.1 billion years ago and dates only the loss of the sulphur signal to 2.4 to 2.3; Poulton and others put permanent oxygenation at about 2.22.

Claim 17 · checked 24 September 2026 · AI-assisted audit

Claim: The marker is subtle:

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: before the rise, sulphur isotopes in sediments fractionate in a way that only happens under ultraviolet light in an oxygen-free atmosphere.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

"Oxygen-free" here means extremely low: the Lyons review puts it below about 0.001 per cent of today’s level.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: The remarkable NMD signals are tied to photochemical reactions at short wavelengths involving gaseous sulphur compounds released from volcanoes into the atmosphere. For the signals to be generated and then preserved in the rock record requires extremely low atmospheric oxygen levels
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 3
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: can produce mass-independent effects and are only possible in an atmosphere almost completely devoid of oxygen
Context
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoIntroduction
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: is thought to originate from the photolysis and/or photoexcitation of volcanogenic SO2 by ultraviolet light in an anoxic atmosphere

Later work looked for

Crossref, 2021 on: Uveges and others (2023) treat the signal as "widely accepted" as a fingerprint of an anoxic atmosphere; nothing changes it.

Claim 19 · checked 24 September 2026 · AI-assisted audit

Claim: The disappearance of that signature is what dates the transition.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: there emerged a far less contentious proof (a ‘smoking gun’) of its timing
Supports
Reconciling discrepant minor sulfur isotope records of the Great Oxidation Eventabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: we demonstrate that the global expression of the CME is barely resolvable; thereby validating S-MIF as a tracer of contemporaneous atmospheric chemistry
Qualifies
The rise of oxygen in Earth’s early ocean and atmospherep. 309
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: sulphur isotope records of NMD fractionation, when viewed through the filter of sedimentary recycling, may complicate efforts to date the GOE precisely

What this does not establish

Recycled sulphur could carry the old signal after oxygen rose, which the Lyons review says may complicate precise dating; a 2023 analysis finds that effect barely resolvable.

Later work looked for

Crossref, 2021 on: Uveges and others (2023) find the recycling effect the Lyons review worried about barely resolvable, which strengthens the signal as a date.

Claim 20 · checked 24 September 2026 · AI-assisted audit

Claim: Oxygen then rose and fell again before settling low for more than a billion years,

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: After the GOE, we assert that oxygen rose again and then fell in the atmosphere and remained, with relatively minor exceptions, at extremely low levels for more than a billion years.

What this does not establish

The rise and fall is the Lyons review’s emerging model, which it calls an assertion; how low "low" was is disputed (claim 22).

Later work looked for

Crossref, 2016 on, "mid-Proterozoic atmospheric oxygen levels": Canfield and others (2021) put the minimum at 2 to 24 per cent of present levels, against the review’s perhaps under 0.1 per cent; page now reports the disagreement.

Corrected

24 September 2026. Previously: “Oxygen then rose and fell again before settling low, perhaps less than one per cent of modern values, for most of the next two billion years, and rising again in the Neoproterozoic to something approaching today’s.” "Perhaps less than one per cent" matched neither side of a live disagreement: the review the page cites says perhaps under 0.1 per cent, and Canfield and others (2021) put the minimum at 2 to 24 per cent. "Most of the next two billion years" overstated the low interval, which the review gives as more than a billion. And the 2023 Mills review has oxygen at 5 to 10 per cent of the atmosphere in the Cambrian and 15 to 20 only by the Devonian, not near today’s in the Neoproterozoic.

Claim 21 · checked 24 September 2026 · AI-assisted audit

Claim: at a level still argued over: a 2014 review suggests perhaps less than a tenth of one per cent of today’s, and a 2021 study of how ancient organic matter weathered puts the minimum at 2 to 24 per cent.

Kind: Disputed. A contested point, where the page reports a side or the disagreement.
Review: Partly checked. Only part of the source could be read. What was not read is listed.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 311
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Oxygen was probably persistently or transiently very low in the atmosphere, perhaps even less than 0.1% of that present today
Supports
Petrographic carbon in ancient sediments constrains Proterozoic Era atmospheric oxygen levelsabstract
Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record · Measurement
The source reads: We find that organic matter was effectively oxidized during weathering ... we constrain minimum atmospheric oxygen levels to between 2 to 24% of present levels from the late Paleoproterozoic Era into the Neoproterozoic Era

What this does not establish

The Canfield paper was read as its abstract only. Both are proxy estimates, and the page does not take a side.

Other readings

The Lyons review rests on chromium and manganese evidence for very low levels; Canfield and others rest on how completely organic matter was oxidised during weathering.

Later work looked for

Claim 22 · checked 24 September 2026 · AI-assisted audit

Claim: It rose again from the Neoproterozoic,

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Only near the end of the Proterozoic did oxygen take a big step up again

Later work looked for

Crossref, 2020 on, "Neoproterozoic oxygenation event": nothing read that settles the order of cause; the 2023 Phanerozoic review extends the rise into the Devonian; page updated.

Claim 23 · checked 24 September 2026 · AI-assisted audit

Claim: though on a 2023 consensus curve it reached 15 to 20 per cent of the atmosphere only in the Devonian.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: We conclude that O 2 probably made up around 5–10% of the atmosphere during the Cambrian and rose in pulses to 15–20% in the Devonian, reaching a further peak of greater than 25% in the Permo-Carboniferous before declining toward the present day.
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 3
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: From the Great Oxidation Event through to the Cambrian, an upper limit on oxygen levels of about 12% of the atmosphere

What this does not establish

The curve is the review’s attempt at a consensus from the methods it judges reliable; it describes itself as a first attempt.

Later work looked for

Claim 24 · checked 24 September 2026 · AI-assisted audit

Claim: Two steps and a long wait

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: ~2.5 billion years ago

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 309
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: come from 2.5-Gyr-old organic-rich shales drilled in Western Australia

Later work looked for

Crossref, 2021 on: Nature Geoscience (2025) reports fluctuating seawater oxygen before the Great Oxidation Event, read as a title only; nothing that moves the date.

Claim 26 · checked 24 September 2026 · AI-assisted audit

Claim: Oxygen-producing photosynthesis is probably operating, on the evidence of trace-metal whiffs of oxygen, before the atmosphere changes for good.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 308
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: many researchers interpret strong trace-metal enrichments in marine sediments as convincing signatures of significant oxidative weathering of pyrite and other sulphide minerals on land long before the GOE
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 309
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Parsimony currently lies with O2-related processes.

What this does not establish

The whiffs imply oxygen in the atmosphere, briefly, so the atmosphere did change before the Great Oxidation Event; what changed then was permanence. Local oxygen oases are a possibility the review raises, not evidence.

Later work looked for

Crossref, 2021 on: nothing read that overturns the whiffs; the review itself notes some controversy about the proxies.

Corrected

24 September 2026. Previously: “Oxygen-producing photosynthesis is operating, on evidence of trace-metal whiffs and local oxygen oases, well before the atmosphere changes.” The review offers oases as a possibility, not as evidence, and reads the whiffs as oxygen reaching the atmosphere, so the atmosphere had changed transiently; the review also calls the interpretation parsimonious rather than settled.

Claim 27 · checked 24 September 2026 · AI-assisted audit

Claim: ~2.4 to 2.3 billion

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: the disappearance of distinctive non-mass-dependent (NMD) sulphur isotope fractionations in sedimentary rocks deposited after about 2.4–2.3 Gyr ago

Later work looked for

Claim 28 · checked 24 September 2026 · AI-assisted audit

Claim: The Great Oxidation Event. The sulphur isotope signature of an oxygen-free atmosphere disappears worldwide.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: the disappearance of distinctive non-mass-dependent (NMD) sulphur isotope fractionations in sedimentary rocks deposited after about 2.4–2.3 Gyr ago
Supports
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoIntroduction
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: anomalous sulfur isotope fractionation in sulfate and sulfide minerals in Archean and early Paleoproterozoic sedimentary rocks and their absence from younger strata

What this does not establish

It returns briefly in a few South African beds after 2.3 billion years ago (claims 40 and 41).

Later work looked for

Claim 29 · checked 24 September 2026 · AI-assisted audit

Claim: 1.8 to 0.8 billion

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 311, Oxygen and life during Earth’s middle age
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: modelling a persistence of low marine oxygen conditions throughout the mid-Proterozoic from roughly 1.8 to 0.8 Gyr ago

Later work looked for

Claim 30 · checked 24 September 2026 · AI-assisted audit

Claim: Low and roughly stable oxygen, in an interval whose carbon isotope record is steady enough to be famously called boring.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: within a relatively narrow range ... as expressed in the famously ‘boring’ mid-Proterozoic ... data, which are marked by exceptional consistency through time

What this does not establish

How low is disputed (claim 22); "boring" in the review describes the carbon isotope record.

Later work looked for

Corrected

24 September 2026. Previously: “Low and roughly stable oxygen, an interval long and uneventful enough to have been called the boring billion.” The cited review applies "boring" to the steady carbon isotope record, not to the interval as uneventful; no source read carries the nickname "the boring billion".

Claim 31 · checked 24 September 2026 · AI-assisted audit

Claim: ~0.8 to 0.4 billion

Kind: Historical claim. A statement about the past that historical evidence can test.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: between roughly 0.8 and 0.55 Gyr ago
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedabstract; Figure 2 caption; section 3, charcoal
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: O 2 probably made up around 5–10% of the atmosphere during the Cambrian and rose in pulses to 15–20% in the Devonian ... the existence of wildfires from 430 Ma to present ... the charcoal curve describes a rise in O 2 levels during the Devonian

Later work looked for

Corrected

24 September 2026. Previously: “~0.8 to 0.5 billion” The 2023 Mills review has the rise continuing in pulses to 15 to 20 per cent in the Devonian.

Claim 32 · checked 24 September 2026 · AI-assisted audit

Claim: A second rise, overlapping the appearance of animals and continuing in pulses into the Devonian.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: We conclude that O 2 probably made up around 5–10% of the atmosphere during the Cambrian and rose in pulses to 15–20% in the Devonian, reaching a further peak of greater than 25% in the Permo-Carboniferous before declining toward the present day.
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 1
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: The first animals lived in the ocean and evolved in the Ediacaran period

Later work looked for

Corrected

24 September 2026. Previously: “A second rise, overlapping the appearance of animals.” The Mills consensus curve has the rise continuing well past the end of the Proterozoic.

Claim 33 · checked 24 September 2026 · AI-assisted audit

How quickly it happened

Claim: How quickly it happened

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: A 2016 study dated the transition itself rather than bracketing it, using sulphur isotopes through a continuous sequence in three South African drill cores.

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: We report the transition (that is, from being mass-independent to becoming mass-dependent) in multiple sulfur isotope signals of diagenetic pyrite in a continuous sedimentary sequence in three coeval drill cores in the Transvaal Supergroup, South Africa.
Supports
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoIntroduction
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: However, there have been large gaps in sedimentary sulfur isotope records in South Africa

Later work looked for

Claim 35 · checked 24 September 2026 · AI-assisted audit

Claim: It places the disappearance of the oxygen-free signature at about 2.33 billion years ago and constrains the transition to less than ten million years,

Kind: Observation. Something measured or seen, as the named source reports it.
Review: Source checked. The cited passage was read, and it says this.

Supports
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: These data precisely constrain the GOE to 2.33 billion years ago. The new data suggest that the oxygenation occurred rapidly–within 1 to 10 million years
Supports
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoDiscussion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: our data constrain the termination of the GOE to be within 2316 to 2326 Ma (±7 My)

What this does not establish

The duration rests on an assumed sedimentation rate for about 5 metres of strata. Poulton and others put the first rise above the threshold earlier, at about 2.43 billion years ago, and the signal returns briefly after 2.33 (claims 40 and 41).

Later work looked for

Claim 36 · checked 24 September 2026 · AI-assisted audit

Claim: which is fast for a change of this kind.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoDiscussion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: In either case, the GOE took place on a geologically rapid time scale.

Later work looked for

Claim 37 · checked 24 September 2026 · AI-assisted audit

Claim: A transition that fast fits models in which the atmosphere flips between two stable states rather than drifting between them.

Kind: What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review: Source checked. The cited passage was read, and it says this.

Supports
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoDiscussion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Model
The source reads: Such a fast rise of pO2 is consistent with atmospheric modeling results that predict a rapid and irreversible transition from stable anoxic to oxic atmospheres
Supports
Reconciling discrepant minor sulfur isotope records of the Great Oxidation EventImplications for the operation of the atmosphere after 2.33 Ga
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: departing from the conventional view that atmospheric oxygenation occurred as a step function between bistable endmember compositions

Other readings

Uveges and others (2023) read the brief later returns of the signal as an intermediate, unstable state, departing from a clean step between two stable states (claim 41).

Later work looked for

Claim 38 · checked 24 September 2026 · AI-assisted audit

Claim: Whether the flip came from a rise in production or a fall in the sinks is left open.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoDiscussion
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: may provide constraints on the controversial problem of whether the rise of O2 during the GOE was primarily a consequence of an increase in the flux of oxygen sources or a decrease in the flux of oxygen sinks

Later work looked for

Claim 39 · checked 24 September 2026 · AI-assisted audit

Claim: Later work on the same South African succession reads what follows differently: oxygen went on crossing back and forth over the threshold after that date, over about two hundred million years in all, and stayed up only from about 2.22 billion years ago.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Partly checked. Only part of the source could be read. What was not read is listed.

Supports
A 200-million-year delay in permanent atmospheric oxygenationabstract
Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record · Measurement
The source reads: we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago ... Oxygen levels thus fluctuated across the threshold of 10-5 of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving ... at about 2.22 billion years ago
Supports
A 200-million-year delay in permanent atmospheric oxygenationabstract
Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Earth and its record · Measurement
The source reads: as documented by marine sediments from the Transvaal Supergroup, South Africa

What this does not establish

The Poulton paper was read as its abstract only. Its two hundred million years count from the first rise at about 2.43 billion years ago, not from 2.33.

Other readings

Uveges and others (2023) find the later returns of the signal brief (claim 41).

Later work looked for

Corrected

24 September 2026. Previously: “Later work on the same South African succession reads what follows differently: oxygen went on crossing back and forth over the threshold for about two hundred million years, and stayed up only from about 2.22 billion years ago.” Poulton and others count the two hundred million years of fluctuation from about 2.43 billion years ago, not from 2.33, which the old wording implied.

Claim 40 · checked 24 September 2026 · AI-assisted audit

Claim: A 2023 reanalysis of those cores finds the returns to an oxygen-free atmosphere brief, perhaps tens of thousands of years each, and reads them as an unsteady in-between state rather than a clean flip.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
Reconciling discrepant minor sulfur isotope records of the Great Oxidation EventResults, testing the brevity of the S-MIF intervals
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: reduces the temporal duration of the post-2.33 Ga instances of S-MIF by an order of magnitude, thus signalling the return of S-MIF for perhaps tens-of-thousands of years
Supports
Reconciling discrepant minor sulfur isotope records of the Great Oxidation EventImplications for the operation of the atmosphere after 2.33 Ga
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: may signal a protracted, intermediate, and extremely sensitive atmospheric state that was uniquely susceptible to perturbation
Supports
Reconciling discrepant minor sulfur isotope records of the Great Oxidation EventImplications for the operation of the atmosphere after 2.33 Ga
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: departing from the conventional view that atmospheric oxygenation occurred as a step function between bistable endmember compositions
Supports
Reconciling discrepant minor sulfur isotope records of the Great Oxidation EventImplications for the operation of the atmosphere after 2.33 Ga
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Measurement
The source reads: we are unable to explain the transient post-2.3 Ga instances of S-MIF without invoking high-order atmospheric dynamics with episodic relapses toward an anoxic atmospheric state

What this does not establish

The reanalysis accepts that the returns are real atmospheric events; its brevity estimate rests on statistics and on new samples from one core.

Later work looked for

Corrected

24 September 2026. Previously: “” Added: the currency search found Uveges and others (2023), who reanalyse the same cores, find the relapses Poulton and others report brief, and dispute the two-stable-states reading.

Claim 41 · checked 24 September 2026 · AI-assisted audit

Making it is not the same as keeping it

Claim: Making it is not the same as keeping it

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: However, the accumulation of O2 in the atmosphere is not simply a matter of determining rates of photosynthesis.

Later work looked for

How the carbon and oxygen cycle works; not a finding later work revises.

Claim 42 · checked 24 September 2026 · AI-assisted audit

Claim: Photosynthesis and respiration nearly cancel: what one produces, the other consumes.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: almost all of the oxygen generated through photosynthesis (more than 99%) is consumed rapidly during aerobic respiration

Later work looked for

How the carbon and oxygen cycle works; not a finding later work revises.

Claim 43 · checked 24 September 2026 · AI-assisted audit

Claim: Oxygen only accumulates when organic carbon, and sulphur as pyrite, is buried before it can be oxidised, which takes it out of the cycle.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: The tiny fraction of organic carbon that is buried is responsible for the rise of oxygen to modern levels ... every mole of pyrite sulfur buried in sediments represents 2 moles of photosynthetic O 2 that remains in the surface environment
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 310
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: some of that primary production in the surface ocean must escape this short-term recycling and become buried long-term beneath the sea floor

Later work looked for

How the carbon and oxygen cycle works; not a finding later work revises.

Corrected

24 September 2026. Previously: “Oxygen only accumulates when organic carbon is buried before it can be oxidised, which takes it out of the cycle.” The Mills review counts pyrite burial as a net oxygen source alongside organic carbon.

Claim 44 · checked 24 September 2026 · AI-assisted audit

Claim: So the long-term oxygen level is set by burial and by the supply of reducing material from volcanoes and weathering, rather than simply by how much photosynthesis is happening.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2, What controls O2 levels
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: in the long-term carbon cycle the net O 2 source linked to carbon and pyrite burial is matched by the sinks through oxidation of fossil organic carbon or pyrite sulfur in ancient sediments, either directly during exposure and weathering or through metamorphism
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: However, the accumulation of O2 in the atmosphere is not simply a matter of determining rates of photosynthesis.
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, opening paragraphs
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: offset by consumption during reactions with reduced compounds emanating from Earth’s interior (such as reduced forms of hydrogen, carbon, sulphur and iron)

Later work looked for

How the carbon and oxygen cycle works; not a finding later work revises.

Corrected

24 September 2026. Previously: “So the long-term oxygen level is set by geology, by burial and by the supply of reducing material from volcanoes and weathering, rather than by how much photosynthesis is happening.” The Mills review says accumulation is "not simply" a matter of photosynthesis, not that photosynthesis plays no part; the proposed fire and plant feedbacks (claim 64) work through productivity, so "set by geology" was dropped.

Claim 45 · checked 24 September 2026 · AI-assisted audit

Why then

Claim: Why then

Kind: Framing. Signposting. It asserts nothing a source could check.

Why the delay

Claim: Why the delay

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: Evidence for oxygen production hundreds of millions of years before the atmosphere changed implies that something consumed it for a very long time,

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 310
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: a balance between carbon burial and compensatory buffering must have initially permitted appreciable oxygen production via photosynthesis without permanent accumulation in the atmosphere
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 310
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: and transiently perhaps hundreds of millions of years earlier
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: has been active on Earth for at least 2.7 billion years, and perhaps much longer

Other readings

A minority argue there was no delay (claim 49).

Later work looked for

Crossref, 2021 on, "Great Oxidation Event": work on sinks continues (a 2022 Science Advances paper proposes a mantle source, read as a title only); nothing that closes it.

Claim 48 · checked 24 September 2026 · AI-assisted audit

Claim: though a minority of researchers argue that the metabolism appeared only at the Great Oxidation Event, leaving no delay to explain.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Other researchers have issued a minority report challenging the need for buffers, arguing instead that the first O2-yielding photosynthesis was coincident with the GOE

What this does not establish

The review records this as a minority view in 2014.

Later work looked for

Not searched beyond the review; the review is the source for the minority position being a minority.

Corrected

24 September 2026. Previously: “” Added: the cited review reports a minority who dispute the delay the passage takes as given.

Claim 49 · checked 24 September 2026 · AI-assisted audit

Claim: Candidate sinks include reduced volcanic gases and dissolved iron in the ocean, whose supply may have waned as the continents grew,

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307, opening paragraphs
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: offset by consumption during reactions with reduced compounds emanating from Earth’s interior (such as reduced forms of hydrogen, carbon, sulphur and iron)
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: tied perhaps to early patterns of volcanism and their relationships to initial formation and stabilization of the continents
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 310
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: a shift from dominantly submarine to increasingly subaerial volcanism as continents grew and stabilized could have led to release of more oxidized gases

Later work looked for

Crossref, 2021 on: the mantle and volcanic sinks remain candidates; nothing read that settles them.

Corrected

24 September 2026. Previously: “Candidate sinks include volcanic gases, dissolved iron in the ocean and the composition of the crust,” The review names reduced gases and ions from the interior as the sinks and ties their decline to the growth of the continents; it does not name the composition of the crust as a sink.

Claim 50 · checked 24 September 2026 · AI-assisted audit

Claim: and the relative sizes of these are not agreed.

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 310
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Recent buffer models generally assume that the redox state of the mantle and magmas derived from it did not change significantly leading up to the GOE
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 310
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: an idea that no doubt will be revisited in future work

Claim 51 · checked 24 September 2026 · AI-assisted audit

Claim: The gap between a metabolism appearing and its waste product accumulating has neither a settled length nor a settled explanation:

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Yet despite decades of intensive investigation, there is no consensus.

Corrected

24 September 2026. Previously: “The gap between a metabolism appearing and its waste product accumulating is one of the longest lags in the planet’s history and it has no settled explanation.” No source read ranks the lag against others in Earth’s history, and its length is itself unknown because the origin of oxygen-producing photosynthesis is not agreed.

Claim 52 · checked 24 September 2026 · AI-assisted audit

Claim: estimates for when the metabolism appeared span well over a billion years.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 307
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Current estimates span well over a billion years

Later work looked for

The 2023 Mills review gives at least 2.7 billion years "and perhaps much longer"; nothing read narrows the range.

Claim 53 · checked 24 September 2026 · AI-assisted audit

Why the second rise

Claim: Why the second rise

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: The Neoproterozoic increase coincides with the snowball glaciations and with the appearance of animals,

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: the emergence of animals is typically attributed to a second big O2step long after the GOE
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: shifts in nutrient cycles at the end of the Marinoan ‘Snowball Earth’ glaciation, the second of two major ice ages in the Neoproterozoic, may have triggered the organic productivity/burial that then spawned the rise in oxygen in the early Ediacaran

Later work looked for

Crossref, 2020 on, "Neoproterozoic oxygenation event": nothing read that settles the order of cause; the 2023 Phanerozoic review extends the rise into the Devonian; page updated.

Claim 55 · checked 24 September 2026 · AI-assisted audit

Claim: and each has been proposed as a cause of another: oxygen for animals, animals for oxygen, glaciation for oxygen and oxygen for glaciation.

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: but animals are just as often cited as evidence for the oxygenation
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: that the generally concurrent rise of animals and oxygen was mostly a coincidence or, alternatively, that animal evolution itself triggered the oxygenation event
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: shifts in nutrient cycles at the end of the Marinoan ‘Snowball Earth’ glaciation, the second of two major ice ages in the Neoproterozoic, may have triggered the organic productivity/burial that then spawned the rise in oxygen in the early Ediacaran
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: as well as the possibility of earlier, even pre-Snowball Earth, oxygenation that may have helped trigger the climate events that followed

Other readings

Butterfield, as the review reports, also allows that the concurrence was mostly coincidence.

Later work looked for

Crossref, 2020 on, "Neoproterozoic oxygenation event": nothing read that settles the order of cause; the 2023 Phanerozoic review extends the rise into the Devonian; page updated.

Corrected

24 September 2026. Previously: “and every ordering of those three has been proposed as causal.” The review carries four causal proposals, not every ordering; nothing read proposes animals causing the glaciations or the reverse.

Claim 56 · checked 24 September 2026 · AI-assisted audit

Claim: The geochemical proxies for oxygen in this interval seem to contradict one another,

Kind: What scholars argue. A report of what specialists argue, or where they disagree.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Other data point instead, in seeming contradiction, to a persistence of expansive anoxic (iron-rich, that is, ferruginous, and euxinic) marine waters
Supports
The rise of oxygen in Earth’s early ocean and atmospherep. 313
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: Amidst the apparent confusion, new research is steering us towards consistent threads

Later work looked for

Crossref, 2020 on, "Neoproterozoic oxygenation event": nothing read that settles the order of cause; the 2023 Phanerozoic review extends the rise into the Devonian; page updated.

Corrected

24 September 2026. Previously: “The geochemical proxies for oxygen in this interval contradict one another,” The review calls the contradiction "seeming" and describes work reconciling it.

Claim 57 · checked 24 September 2026 · AI-assisted audit

Claim: which is the honest reason the story keeps changing.

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s reading of the proxy disagreement the review describes.

Claim 58 · checked 24 September 2026 · AI-assisted audit

Why it stays

Claim: Why it stays

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: The level is set by what gets buried, not by what gets made.

Kind: This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review: A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

A compression of claim 45: burial is the long-term source.

Context
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 2
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: However, the accumulation of O2 in the atmosphere is not simply a matter of determining rates of photosynthesis.

Other readings

What gets made still matters through burial: the proposed phosphorus and fire feedbacks act on productivity (claim 64).

Claim 60 · checked 24 September 2026 · AI-assisted audit

What holds it steady now

Claim: What holds it steady now

Kind: Framing. Signposting. It asserts nothing a source could check.

Claim: Atmospheric oxygen has stayed within about a factor of two of today’s level for the last four hundred million years.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedabstract
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: We conclude that O 2 probably made up around 5–10% of the atmosphere during the Cambrian and rose in pulses to 15–20% in the Devonian, reaching a further peak of greater than 25% in the Permo-Carboniferous before declining toward the present day.
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 3, Long-term O2 constraints
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: A much more certain lower limit exists from the mid-Silurian onward and is defined by the presence of inertinite in sediments between 430 and 0 Ma. ... Experiments have determined that fires cannot sustain themselves below 15% O2
Supports
Combined effects of photorespiration and fire strongly regulate atmospheric oxygen levelsIntroduction, first paragraph
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Model
The source reads: Since the establishment of forest ecosystems ~420 million years ago (Ma), atmospheric oxygen (O2) has remained at broadly present atmospheric levels (PALs) (1), estimated to have remained between the range ~15 to 40 vol % O2

What this does not establish

The upper bound is the less certain end: the Vitali paper says the physical upper limit has long been disputed.

Later work looked for

Claim 62 · checked 24 September 2026 · AI-assisted audit

Claim: The floor is read from charcoal, which needs roughly fifteen per cent oxygen to form and is in the record from the mid-Silurian on, with gaps whose meaning is uncertain.

Kind: What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review: Source checked. The cited passage was read, and it says this.

Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 3, Long-term O2 constraints
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: A much more certain lower limit exists from the mid-Silurian onward and is defined by the presence of inertinite in sediments between 430 and 0 Ma. ... Experiments have determined that fires cannot sustain themselves below 15% O2
Supports
Evolution of Atmospheric O2 Through the Phanerozoic, Revisitedsection 3
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Earth and its record · Review of the field
The source reads: when inertinite is sparsely recorded or absent, and it is uncertain if this is related to low pO2 or unfavorable conditions for preservation

Later work looked for

Corrected

24 September 2026. Previously: “and is in the record continuously from the mid-Silurian.” The review names periods, in the Devonian, Early Triassic and very Early Cretaceous, when inertinite is sparse or absent, and says it is uncertain whether that reflects low oxygen or preservation.

Claim 63 · checked 24 September 2026 · AI-assisted audit

Claim: Feedbacks involving phosphorus, fire, the slowing of plant growth at high oxygen and the burial of organic carbon are proposed to hold it there.

Kind: Hypothesis. A proposed explanation, not an established one.
Review: Source checked. The cited passage was read, and it says this.

Supports
The rise of angiosperms strengthened fire feedbacks and improved the regulation of atmospheric oxygenIntroduction
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Model
The source reads: Increases in phosphorus result in enhanced productivity and increased organic carbon burial which prevents atmospheric oxygen from falling too low
Supports
The rise of angiosperms strengthened fire feedbacks and improved the regulation of atmospheric oxygenIntroduction
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Model
The source reads: It is suggested that high fire frequency and intensity regulate atmospheric oxygen by suppressing plant growth and biomass production on land, meaning that less organic material is available for carbon burial
Supports
Combined effects of photorespiration and fire strongly regulate atmospheric oxygen levelsIntroduction
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Model
The source reads: Increasing the oxygen mixing ratio causes an inhibitory effect on photosynthetic CO2 fixation and increases photorespiration, resulting in lower productivity

What this does not establish

All are model results; the Vitali paper says the effectiveness of photorespiration as a regulator had not been established before its own modelling.

Later work looked for

Europe PMC, open access, "atmospheric oxygen" with regulation, fire and phosphorus: Belcher and others (2021) and Vitali and others (2026), the latter adding photorespiration and questioning the strength of fire alone; page updated.

Corrected

24 September 2026. Previously: “Feedbacks involving phosphorus, fire and the burial of organic carbon are proposed” The passage cited only a review that does not discuss these feedbacks; the Belcher (2021) and Vitali (2026) papers carry them, and the 2026 paper adds photorespiration as a candidate.

Claim 64 · checked 24 September 2026 · AI-assisted audit

Claim: Which of them does the work is not agreed, and the stability remains better observed than explained.

Kind: Open question. Something the page says is not known.
Review: Presented as open. The page says this is unresolved, and the review found that it is.

Supports
Combined effects of photorespiration and fire strongly regulate atmospheric oxygen levelsIntroduction
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Model
The source reads: Despite decades of work on this problem, the supposed tight regulation of oxygen levels has remained largely untested and the physical upper limit of atmospheric O2 on Earth has been long disputed.
Supports
Combined effects of photorespiration and fire strongly regulate atmospheric oxygen levelsIntroduction
Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Model
The source reads: dynamic vegetation modeling under changing O2 levels questions the strength of the fire feedback at the global scale

Claim 65 · checked 24 September 2026 · AI-assisted audit

What was read

The rise of oxygen in Earth’s early ocean and atmosphereLyons, Reinhard and Planavsky, Nature · Nature 506:307–315, published PDF as hosted for teaching at eoas.ubc.ca; read in fullRead in full, 24 September 2026 · Copyright; quoted brieflyPDF text extraction joins "O2" to the next word in places; excerpts keep that spacing so they can be matched.
Rapid oxygenation of Earth’s atmosphere 2.33 billion years agoLuo and others, Science Advances · Europe PMC full text, PMC4928975Read in full, 24 September 2026 · CC BY-NC 4.0
A 200-million-year delay in permanent atmospheric oxygenationPoulton and others, Nature · Europe PMC abstract (PMID 33782617); the accepted manuscript on the SDU research portal returned 403Abstract only, 24 September 2026 · Copyright; quoted briefly
Evolution of Atmospheric O2 Through the Phanerozoic, RevisitedMills, Krause, Jarvis and Cramer, Annual Review of Earth and Planetary Sciences · Published version text, UCL Discovery repository copy; read abstract and sections 1 to 3, 4.1.3, 4.3.1 and 6 to 7Read in full, 24 September 2026 · CC BY 4.0
Reconciling discrepant minor sulfur isotope records of the Great Oxidation EventUveges, Izon, Ono, Beukes and Summons, Nature Communications · Europe PMC full text, PMC9845385; read abstract, results and discussionRead in full, 24 September 2026 · CC BY 4.0
Petrographic carbon in ancient sediments constrains Proterozoic Era atmospheric oxygen levelsCanfield and others, Proceedings of the National Academy of Sciences · Europe PMC abstract; full text (PMC8201950) returned error 500Abstract only, 24 September 2026 · Copyright; quoted briefly
The rise of angiosperms strengthened fire feedbacks and improved the regulation of atmospheric oxygenBelcher and others, Nature Communications · Europe PMC full text, PMC7820256; read abstract and introductionRead in full, 24 September 2026 · CC BY 4.0
Combined effects of photorespiration and fire strongly regulate atmospheric oxygen levelsVitali, Belcher, Mills and Watson, Science Advances · Europe PMC full text, PMC12778039; read abstract, introduction and first results sectionRead in full, 24 September 2026 · CC BY 4.0