Global-scale emergence of continental crust during the Mesoarchean–early Neoarchean
Bibliographic record
Abstract
Abstract The timing of the emergence of subaerial landmasses is equivocally constrained as post-Archean and continues to be a much-debated issue. In this study, we document exceptionally 18O-depleted (δ18O < 4.7‰) Mesoarchean to early Neoarchean magmatism in India that shows a similarity with the coeval low-δ18O magmas reported from Australia, South America, and northern China. Such global-scale low-δ18O magmatism would require high-temperature meteoric water–rock interaction in the uppermost crust synchronous with magma generation, necessitating the emergence of a substantial volume of the continental crust. The timing of this low-δ18O magmatism coincides with the development of extensive, subaerial large igneous provinces, a downward shift in δ18O and Δ17O values in pelitic rocks, the rise of normalized 87Sr/86Sr in seawater, and an intermittent upsurge in the proportion of atmospheric oxygen. We propose that the emergence of substantial volumes of continental crust initiated at ca. 3.2 Ga and peaked at 2.8–2.6 Ga, facilitating the generation of globally distributed low-δ18O magmas, and this event can be linked to the first appearance of atmospheric oxygen.
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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 | 0.000 |
| 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".