For nearly the whole span of Earth's history, the air held almost no oxygen, and the living world was shaped by that scarcity. A review in The Innovation, from two geochemists at Chengdu University of Technology, suggests that this gas arrived in three uneven stages rather than one great turn, and that the deep ocean lagged behind each of them for long stretches of time. Their method reads the faint oxygen-17 fingerprint preserved in ancient sulfate minerals, a record of the air itself rather than the sea that merely mirrors it. In doing so they reframe the slow emergence of an oxygen-rich pla
Earth's Air Gained Oxygen in Three Steps, and the Deep Ocean Lagged Each Time
The ocean did not lead the atmosphere; it followed, slowly.
Mark
Why does it matter that the air got oxygen before the ocean did?
Mimi
Because the usual textbook events, the Neoproterozoic and Paleozoic oxygenations, get reinterpreted. They become the ocean catching up, about 200 and 30 million years behind the atmosphere.
Mark
And the evidence is sulfate?
Mimi
Yes. Atmospheric oxygen has an oxygen-17 deficit from O2–O3–CO2 photochemistry, and weathering sulfide minerals passes that fingerprint into sulfate preserved in sediments.
Luke
Worth flagging that this is a review making an argument, not a single new measurement. And the authors admit isotope resolution is coarse.
Mark
So how firm are the dates?
Luke
The ranges are wide, like 1.3 to 1.0 billion years, and absolute oxygen levels after 1.0 billion years ago are described as poorly constrained. The ordering is the claim, not precise numbers.
Mimi
The ordering is the point. Ocean redox responds to nutrients, circulation and basin shape too, so it was never a clean proxy for air.
Mark
What about spikes in the record?
Mimi
The authors say some may mark oxygen retreating, since oxygen entering the ocean gets consumed oxidising organic carbon and sulfide.
Luke
That's an interpretation offered as possible for many spikes. The source doesn't say which ones.
Mark
And life?
Mimi
Oxygen went from a hard limit to a permissive one, and only after the third rise did it amplify complexity, like larger bodies and active predation.
El Pulso
- A new review argues atmospheric oxygen climbed in three uneven steps, with the deep ocean trailing each one by hundreds of millions of years.
- Earlier oxygenation timelines built on seawater chemistry are being called into question, as ocean signals prove a noisy stand-in for the air.
- Researchers are turning to oxygen-17 signatures locked in ancient sulfate minerals to read the atmosphere directly.
- The second and third oxygen rises arrive roughly 1.3 to 1.0 and 0.44 to 0.41 billion years ago, well ahead of classic dates.
- The deep ocean did not fully oxygenate until about 0.41 billion years ago, a delay the authors tie to key biological change.
For nearly the whole span of Earth's history, the air held almost no oxygen, and the living world was shaped by that scarcity. A review in The Innovation, from two geochemists at Chengdu University of Technology, suggests that this gas arrived in three uneven stages rather than one great turn, and that the deep ocean lagged behind each of them for long stretches of time. Their method reads the faint oxygen-17 fingerprint preserved in ancient sulfate minerals, a record of the air itself rather than the sea that merely mirrors it. In doing so they reframe the slow emergence of an oxygen-rich planet as a story in which the ocean followed, and in following, life found much of its room to change.
For most of Earth's history, the air held almost nothing worth breathing. A review in The Innovation, written by two geochemists at Chengdu University of Technology, argues that oxygen arrived in three uneven steps, and that the deep ocean trailed behind each one, in the last case by roughly 600 million years.
The authors changed the evidence. Earlier accounts read ancient seawater chemistry as a stand-in for the air, but the ocean depends on nutrients, biology, circulation and basin shape, making it a poor witness. Instead they use sulfate. Atmospheric oxygen carries a distinctive oxygen-17 deficit, and that signature passes into sedimentary sulfate, turning the rock record into an archive of the air.
The first rise is the familiar Great Oxidation Event, around 2.4 to 2.1 billion years ago. The second and third come earlier than textbooks suggest, at 1.3 to 1.0 and 0.44 to 0.41 billion years ago. The later ocean oxygenation events are recast as delayed echoes of these atmospheric rises.
Between the second and third steps, oxygen stayed scarce, and charcoal did not appear until about 420 million years ago. The air and sea move together over eons but can diverge over shorter spans. The authors acknowledge coarse data and remaining uncertainty, yet their core point holds: the ocean followed the air slowly, and that delay is where much of the biology unfolded.
For most of Earth's history there was nothing in the air worth breathing. A review in The Innovation, written by two geochemists at Chengdu University of Technology, argues that oxygen arrived in the atmosphere in three uneven steps, and that the deep ocean trailed behind each one. In the last case the delay ran to roughly 600 million years.
The argument rests on a change of evidence. Earlier accounts read the chemistry of ancient seawater from the rock record and treated it as a stand-in for the air. But the oxygen state of the ocean also depends on nutrients, biological productivity, circulation and the shape of basins, so it is a noisy witness to the atmosphere. The authors turn instead to sulfate. Atmospheric oxygen carries a distinctive deficit in oxygen-17, produced by photochemistry among O2, O3 and CO2. When sulfide minerals weather, that signature passes into sulfate, and sedimentary sulfate keeps it. The rock record of sulfate becomes an archive of the air itself.
Read that way, the first rise is the familiar one. The Great Oxidation Event still falls at 2.4 to 2.1 billion years ago, lifting oxygen from below one part in a million of today's level to somewhere between a thousandth and a tenth of it. The second and third rises come earlier than the textbooks place them: 1.3 to 1.0 billion years ago, and 0.44 to 0.41 billion years ago.
That shift reorders the classic story. The Neoproterozoic and Paleozoic oxygenation events, dated to 0.8 to 0.5 and 0.42 to 0.36 billion years ago, are recast as the ocean's delayed responses to atmospheric rises already under way. By the review's reckoning they lag the air by roughly 200 million years and 30 million years respectively.
Between the second and third steps, oxygen stayed scarce. Modelling calibrated to the isotope data puts the mid-Proterozoic atmosphere at 0.1 to 1 percent of the modern level. Charcoal, which needs about three-quarters of today's oxygen to burn, does not appear until around 420 million years ago.
The air and the sea are coupled, but not in a simple way. Over a billion years they rise together. Over a million they can move apart, because a pulse of oxygen into the ocean oxidises stored organic carbon and sulfide, consuming the gas and pulling atmospheric levels down. The authors suggest that many spikes once read as rising oxygen may instead mark its retreat.
Ocean oxygenation was also patchy. Two regimes coexisted: oxygen made locally by photosynthetic microbes, which opened oxygen oases from 3 billion years ago or earlier, and oxygen delivered from the atmosphere. The first dominated the Archean; the second took over as the air thickened. A fully oxygenated ocean interior did not arrive until about 0.41 billion years ago.
Life followed these conditions without being simply triggered by them. Under anoxic air, oxygen was a hard limit. Through the Proterozoic it became a permissive one, opening niches while animals evolved amid fluctuating levels. Only after the third rise, the authors say, did oxygen actively amplify complexity, in the form of larger bodies, active predation and deeper habitats.
The authors acknowledge limits: isotope resolution is coarse, absolute oxygen levels after 1.0 billion years ago remain poorly constrained, and further steps in the transition may be invisible in the record. What the review changes is the order of events. The ocean did not lead the atmosphere into an oxygenated world; it followed slowly, and the delay is where much of the biology happened.
Citas Notables
The ocean did not lead the atmosphere into an oxygenated world; it followed, slowly, and the delay is where the biology happened.— Review authors, Chengdu University of Technology, in The Innovation (paraphrased)
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