Slow net sediment accumulation sets snowball Earth apart from all younger glacial episodes
Bibliographic record
Abstract
Abstract During the Sturtian and Marinoan “snowball Earth” episodes, ice cover is thought to have extended from polar to tropical latitudes. We test the supposition that such an extreme glacial climate, not repeated in the subsequent ∼635 m.y. of Earth history, would have reduced the vigor of the hydrologic cycle and thus diminished sediment flux to the oceans. With >500 sediment accumulation rates to characterize Sturtian and Marinoan deposits, we find median accumulation rates at least four to 15 times slower than expected for Phanerozoic glaciomarine deposits as characterized by >10,000 rates. Our comparison is conservative with respect to time span, latitude, and distance from the ice margin. Phanerozoic accumulation rates decrease systematically when averaged over longer time spans. Comparisons were drawn, therefore, at 5 and 57 m.y. time spans to match minimum Marinoan and Sturtian durations, respectively. Cenozoic glaciomarine accumulation also slows with increasing latitude from temperate to polar climates and with increasing distance from the ice margin. After accounting for time span, snowball Earth deposits at low latitude are found to be thinner than would be expected either for high-latitude Cenozoic glacial deposits or for very distal glaciomarine abyssal muds with ice-rafted debris. The rate discrepancy is not readily attributed to overestimates of the total Marinoan or Sturtian durations. If sediment fluxes during warm melt intervals did approach Phanerozoic rates, these intervals must have occupied a much smaller proportion of snowball Earth episodes than in younger glacial climates.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".