CTE HNICAL COMMENTS-s,A V;..'h-, Sm-Nd Isotopic Data and Earth's Evolution
Bibliographic record
Abstract
report Sm/Nd isotopic data giving a wide range of initial ENd values, from +3.5 to-4 at 4.0 billion years ago (Ga) and from +4 to-7 at 3.6 Ga. Their samples were from the Acasta gneisses of northern Canada, which represent the oldest known outcrops of con-tinental crust (2). Their modeling of the Sm-Nd isotopic data is taken to suggest that the Acasta granitoid rocks were formed from mixtures between mantle-derived melts and crustal melts derived from ex-tremely ancient (about 4.3 Ga), heteroge-neous, depleted (high Sm/Nd) and enriched (low Sm/Nd) reservoirs. We consider it likely that the wide range of initial ENd values has a much simpler explanation. We plot the Acasta gneiss Sm-Nd data of Bowring and Housh (1) and Bowring et al. (3) on a Sm-Nd isochron diagram (Fig. 1). Ten out of 13 points define a well-correlated regression line ("errorchron"), yielding an age of 3239 + 150 million years ago (Ma) (2 a ' errors; MSWD = 36), with an initial EN.l value of-7.9 ± 1.8. These data points are based on samples for which SHRIMP ion-microprobe zircon U-Pb dates range between 4.0 and 3.6 Ga (1, 3). If we consider only those samples with the oldest zircon U-Pb dates of about 4.0 Ga, the regression age for five out of six samples is 3156 + 100 Ma (MSWD = 6.4) and the initial ENd value is-9.0 + 1.3 (Fig. 1). We therefore propose that the Acasta gneisses suffered a tectonothermal event at about 3.2 Ga that caused open-system be-havior of Sm-Nd and resulted in an approx-
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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 | 0.002 | 0.017 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.321 | 0.104 |
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".