Breathing life into the boring billion: Direct constraints from 1.4 Ga fluid inclusions reveal a fair climate and oxygenated atmosphere
Bibliographic record
Abstract
The Mesoproterozoic eon [1.8 to 0.8 billion years ago (Ga)] is a crucial but enigmatic period in Earth’s history. Many facets of this interval remain unresolved, especially how atmospheric evolution influenced and responded to changes in climate and biology. For example, low atmospheric O 2 concentrations are thought to have inhibited the emergence of animals until the Neoproterozoic. Yet, some p O 2 estimates indicate that the critical threshold for animal respiration was exceeded several hundred million years prior. Likewise, low p CO 2 estimates imply glacial climates should prevail. However, this prediction is inconsistent with an apparent billion-year hiatus in glaciation. We test these hypotheses with direct constraints on the Mesoproterozoic atmosphere from analyses of primary fluid inclusions in 1.4 Ga surficial halite, which reveal an atmospheric p O 2 of 7.84 ± 3.05 mbar and a p CO 2 of 2.76 ± 1.66 mbar. We couple these measurements with average inclusion homogenization temperatures of 31.2 ± 7.8 °C. Our results point to an Earth system state characterized by a moderate climate with sufficient O 2 for early animal respiration. These observations reflect a coevolution of life, climate, and the atmosphere, where a largely unrecognized episode of oxygenation and CO 2 drawdown was driven by the breakup of the supercontinent Nuna and the complexification of algal eukaryotes.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 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) | 0.001 | 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".