Marine sulphate captures a Paleozoic transition to a modern terrestrial weathering environment
Bibliographic record
Abstract
The triple oxygen isotope composition of sulphate minerals has been used to constrain the evolution of Earth’s surface environment (e.g., pO2, pCO2 and gross primary productivity) throughout the Proterozoic Eon. This approach presumes the incorporation of atmospheric O2 atoms into riverine sulphate via the oxidative weathering of pyrite. However, this is not borne out in recent geological or modern sulphate records, where an atmospheric signal is imperceptible and where terrestrial pyrite weathering occurs predominantly in bedrock fractures that are physically more removed from atmospheric O2. To better define the transition from a Proterozoic to a modern-like weathering regime, here we present new measurements from twelve marine evaporite basins spanning the Phanerozoic. These data display a step-like transition in the triple oxygen isotope composition of evaporite sulphate during the mid-Paleozoic (420 to 387.7 million years ago). We propose that the evolution of early root systems deepened the locus of pyrite oxidation and reduced the incorporation of O2 into sulphate. Further, the early Devonian proliferation of land plants increased terrestrial organic carbon burial, releasing free oxygen that fueled increased redox recycling of soil-bound iron and resulted in the final rise in pO2 to modern-like levels. Ancient sulfate mineral compositions reflect an increase in Earth’s oxidation state ~400 million years ago, likely including an increase in atmospheric oxygen levels and shift in mineral weathering pathways.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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 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".