Oldest reliable terrestrial <sup>40</sup>Ar‐<sup>39</sup>Ar age from pyrite crystals at Isua west Greenland
Bibliographic record
Abstract
Pyrite grains can act as K‐Ar time capsules, by armoring the minute inclusions hosted within the pyrite, thus preventing loss of their radiogenic argon. This pyrite clock provides the means to apply single‐crystal laser 40Ar‐39Ar dating to rocks that typically resist straightforward dating, notably sedimentary rocks. We have applied the technique to a banded iron formation from Earth's oldest sequence of sedimentary and volcanic rocks, the Isua greenstone belt of west Greenland. We find that, in spite of having been subjected to several metamorphic and metasomatic events, the mineral inclusions in pyrites from these rocks give remarkably well‐defined and reproducible ages at 3.86 ± 0.07 Ga, in agreement with previous determinations of the age of their host rocks. Moreover, the isotopic data from these pyrites yield distinct indications of inclusions giving an age of 4.31 ± 0.06 Ga, possibly providing the first direct evidence for a much earlier crust at Isua.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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".