The zircon record of the Sudbury impact crater and its implications for the early Earth
Bibliographic record
Abstract
In the absence of widespread rocks older than 4.0 Ga, the earliest terrestrial material and the only direct evidence for the nature of the Earth's very early crust are tiny zircon crystals. The chemical compositions of these Hadean zircons have been used to infer the composition and petrogenesis of the original host rocks and in turn the composition of, and processes acting on, Earth's very early crust. One of the few other relative certainties regarding the early Earth is that it was subjected to intense bolide bombardment. However, despite this being a well-acknowledged fact, very little is known about the effects of impact-induced shock metamorphism and reprocessing on the trace element and stable isotope geochemistry of zircon. Additionally, our knowledge of new zircon which crystallises in impact melt sheets is also very limited. This thesis presents investigations into the geochemistry of newly formed as well as shock metamorphosed zircon from the best preserved and most accessible large impact crater on Earth - the subaqueous, 1.85 Ga Sudbury impact structure, Ontario, Canada - as an analogue for impact craters on the early Earth.
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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 | 0.002 | 0.003 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".