La composition isotopique du molybdène des stromatolites modernes et anciens
Bibliographic record
Abstract
The primitive Earth was characterized by an oxygen-poor ocean–atmosphere system, and experienced a significant increase in oxygen concentrations during the Great Oxidation Event (GOE) ca 2.45 Ga. This event is generally believed to be linked in some way to oxygenic photosynthesis by bacteria. However, it is becoming commonly accepted that “whiffs” of oxygen existed before the GOE. To shed new light on this emerging paradigm, here we present molybdenum (Mo) isotopic data for modern stromatolites from Bacalar lagoon, Mexico, and ancient stromatolites from Archean sediments deposited ca. 2.52 Ga (Ghaap Group, South Africa), 2.8 Ga (Steep Rock, Canada), and 2.96 Ga (Red Lake, Canada). Modern samples record a molybdenum isotopic signature that appears related to the water from which they grew, supporting the idea that the molybdenum isotopic composition of carbonates is a robust proxy for examining paleo-redox conditions of environments where carbonates were precipitated. Ancient stromatolites reveal evidence for oxygen in the environment at 2.96 Ga at 2.8 Ga, while stromatolites from the Ghaap Group (2.52 Ga) appear to have grown under poorly-oxygenated conditions. My data suggests that oxygenic photosynthesis existed yet at least 0.61 Ga before the rise of atmospheric oxygen. Moreover, the consistent signal for oxygen in the environment at this time could be indicative of a constant period of mild oxygenation, rather than local oases as previously proposed.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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 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".