Proliferation of oxygen oases in Mesoarchean oceans
Bibliographic record
Abstract
Abstract Oxygenic photosynthesis played an essential role in the accumulation of free oxygen (O2) at Earth’s surface, but questions persist regarding its evolutionary timeline. Manganese (Mn)-rich sedimentary rocks from the Mesoarchean Pongola Supergroup in South Africa have been invoked among the earliest evidence for O2-dependent Mn(II) oxidation and thus photosynthetic O2 production in oceans. However, as a singular suite of rocks, uncertainties persist about whether the evidence for O2 in the Pongola region has global implications. Here we report on another Mesoarchean Mn-rich iron formation in South China, dating back to ca. 2.88–2.80 Ga. The Dianzihe iron formation exhibits a positive correlation between Mn enrichment (MnO up to 7.08 wt%, Fe/Mn ratio down to 5.1) and negative δ56Fe values (−0.21 to −1.33‰; average = −0.91‰). This pattern requires oxygenated seawater (i.e., O2 > 10 μM) at least to the seafloor, allowing not only for the oxidation of Fe(II) and Mn(II) but also for the preservation of Fe(Mn) oxyhydroxides until post-depositional modifications. Based on our findings in China alongside the distribution of Mn-rich iron formations in South Africa, we posit that a global distribution of oxygen oases, driven by cyanobacterial O2 production, already existed in the Mesoarchean.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".