Mid-Devonian ocean oxygenation enabled the expansion of animals into deeper-water habitats
Bibliographic record
Abstract
The oxygenation history of Earth’s surface environments has had a profound influence on the ecology and evolution of metazoan life. It was traditionally thought that the Neoproterozoic Oxygenation Event enabled the origin of animals in marine environments, followed by their persistence in aerobic marine habitats ever since. However, recent studies of redox proxies (e.g., Fe, Mo, Ce, I) have suggested that low dissolved oxygen levels persisted in the deep ocean until the Late Devonian, when the first heavily wooded ligniophyte forests raised atmospheric O 2 to modern levels. Here, we present a Paleozoic redox proxy record based on selenium enrichments and isotope ratios in fine-grained siliciclastic sediments. Our data reveal transient oxygenation of bottom waters around the Ediacaran–Cambrian boundary, followed by predominantly anoxic deep-water conditions through the Early Devonian (419 to 393 Ma). In the Middle Devonian (393 to 382 Ma), our data document the onset of permanent deep-ocean oxygenation, coincident with the spread of woody biomass across terrestrial landscapes. This episode is concurrent with the ecological occupation and evolutionary radiation of large active invertebrate and vertebrate organisms in deeper oceanic infaunal and epifaunal habitats, suggesting that the burial of recalcitrant wood from the first forests sequestered organic carbon, increased deep marine oxygen levels, and was ultimately responsible for the “mid-Paleozoic marine revolution.”
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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 source (direct Gemma or distilled Codex), 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".