Continental crust had fully emerged by the end of the Paleoproterozoic
Bibliographic record
Abstract
Earth has bimodal hypsometry, with emergent, subaerial continents and submerged oceanic crust. The tempo and history of emergence is imprecisely understood. We estimate the oxygen isotope composition of seawater (δ18OSW) via tracer mass balance inversion of sections of hydrothermally altered ocean crust as a proxy for emergent crust. Using data from Sturgeon Lake, Canada (∼2735 Ma) and the Pecos Greenstone Belt, USA (∼1720 Ma), we find δ18OSW decreased from about +3 to +4 ‰ to −0.2 ‰, indicating near-modern levels of emergence by ∼1720 Ma, with minimal emergence at ∼2735 Ma. We employ a steady state δ18OSW model, driven either by continuous or punctuated continental growth, to interpret our findings. Such reconstructions indicate continental growth and emergence were decoupled until the end of the Archean.
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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 | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".