The air we breathe is the product of planetary-scale cycles that took billions of years to unfold.
Imagine an Earth with no breathable air—a world where oceans span under orange skies, devoid of animal life. For nearly half its history, this was our planet. Then, oxygen began to appear, not in a steady rise, but in dramatic leaps that forever changed Earth's destiny. For decades, scientists debated what caused these stepwise surges. Was it biological revolutions? Tectonic upheavals? Recent research reveals a more fascinating story: Earth's oxygenation followed a natural rhythm inherent to the planet's own biogeochemical cycles.
This article explores how our planet transformed itself through three great oxygenation events—from the first toxic whiffs of oxygen that poisoned ancient microbes to the stable, oxygen-rich atmosphere that eventually enabled our existence.
Earth's atmosphere experienced three major oxygen surges over the past two billion years as it shifted from an anoxic to an oxygen-rich state. These stepwise increases occurred during the Paleoproterozoic era (2.4 to 2.1 billion years ago), the Neoproterozoic era (about 1 billion years ago), and the Paleozoic era (about 440 million years ago) 3 .
Scientists have determined that these three oxygenation steps are a simple consequence of internal feedbacks in the long-term biogeochemical cycles of carbon, oxygen, and phosphorus 4 . No specific stepwise external forcing is required to explain Earth's surface oxygenation—the pattern emerged naturally from the interplay of Earth's systems after the evolution of oxygenic photosynthesis.
One of the most dramatic chapters in Earth's oxygenation story occurred during the later stages of the GOE—the Lomagundi Event (LE). Between approximately 2.22 and 2.06 billion years ago, Earth experienced the largest and longest-lived positive carbon isotope excursion in its history 6 . This event provides crucial clues about how Earth's biogeochemical systems operate.
During the LE, carbonate sediments worldwide recorded unusually high δ¹³C values, with averages around +8‰ and peaks reaching an extraordinary +28‰ 6 .
The LE may have been driven by increased availability of phosphorus (P), a key bio-limiting nutrient 6 . When phosphorus becomes more available in oceans, it can fuel algal blooms and increase oxygen production.
To test the hypothesis that phosphorus availability drove oxygenation events, scientists conducted an innovative study examining carbonate rocks from the GOE period. Their research, published in 2025, used a sophisticated geochemical technique to reconstruct ancient marine phosphorus concentrations 6 .
The research team utilized the Carbonate-Associated Phosphate (CAP) proxy to reconstruct oceanic phosphorus concentrations during the GOE from globally distributed sedimentary rocks 6 .
This method capitalizes on the fact that carbonate minerals incorporate phosphate into their crystal structure proportionally to the elemental concentrations in seawater 6 .
The CAP data revealed a striking pattern: carbonate formations deposited during positive δ¹³C excursions, including the Lomagundi Event, showed significantly higher phosphorus concentrations than those from periods with normal carbon isotope values 6 .
| Geologic Unit | Age (Ga) | CAP During Excursion (mmol/mol) | CAP Outside Excursion (mmol/mol) | Increase Factor |
|---|---|---|---|---|
| Judering Fm. | ~2.1 | 0.408 | - | - |
| Carawine Dolomite | ~2.6 | - | 0.005 | - |
| South Africa | ~2.1 | Higher | Lower | 4.0x |
| Brazil | ~2.1 | Higher | Lower | 3.1x |
| West Australia | ~2.1 | Higher | Lower | 9.2x |
| Wooly Dolomite | ~2.0 | 0.130 | 0.011 | 11.8x |
Biogeochemical modeling accompanying the geochemical data demonstrated that transient increases in phosphorus bioavailability can raise oxygenic primary production and organic carbon burial, yielding isotopically heavy seawater inorganic carbon and reproducing the observed patterns 6 .
Paleogeochemists use sophisticated tools to read the story of Earth's oxygenation. Here are key methods and reagents that help scientists decode billion-year-old rocks:
Reconstructs ancient marine phosphorus concentrations and links nutrient availability to oxygenation events 6 .
Detects atmospheric oxygen levels below 10⁻⁶ PAL and defines timing of GOE 1 .
Indicators of ancient water column redox conditions that track extent of ocean oxygenation 1 .
Distinguishes between ferruginous and euxinic conditions to determine redox state of ancient oceans 1 .
The stepwise pattern of Earth's oxygenation appears to be an inherent property of global biogeochemical cycling rather than requiring external triggers like tectonic catastrophes or biological innovations 4 . The experiments with CAP and phosphorus cycling provide compelling evidence for this view, showing how feedback between nutrients, organic carbon burial, and oxygen creation can produce the observed pattern of rises and plateaus.
This rhythmic rise of oxygen made Earth habitable for complex life. While the first surge enabled eukaryotic life, and the second supported early animals, the third established the stable, oxygen-rich atmosphere that eventually allowed for the evolution of large, active organisms, including humans.
As one researcher noted, these findings offer "new perspectives for exploring the formation of habitable planets" 3 . The same principles that governed oxygen accumulation on Earth may apply to worlds beyond our solar system, helping us identify which distant planets might breathe with the rhythm of life.