The end-Ordovician mass extinction

Assembled from 29 blocks · 2 evidence · 23 related

1. Story
2. Usually reckoned the second most severe of the five by proportion of genera lost, and structurally unlike the others because it is clearly two pulses separated by several hundred thousand years and driven by opposite conditions. A short, intense glaciation on Gondwana — then positioned over the South Pole — locked water into ice, dropped global sea level and drained the shallow epicontinental seas where most marine diversity lived; that is the first pulse. The second came with deglaciation, sea-level rise and the spread of anoxic water back across the shelves. It is the only one of the Big Five in which cooling is the primary driver rather than warming. The graptolites, brachiopods and trilobites were heavily affected, but the event is notable for removing large numbers of species without dismantling the structure of marine ecosystems — the same kinds of organisms in the same kinds of communities resumed afterwards, which is not true of the end-Permian.
3. Knowledge
4. International Commission on Stratigraphy
5. Mass extinction
6. The end-Ordovician mass extinction
7. The Late Devonian crisis
8. Connections
9. The Cambrian explosion
10. Mass extinction
11. The Late Devonian crisis
12. International Commission on Stratigraphy
13. Radiometric dating
14. The end-Permian mass extinction
15. The Cretaceous–Palaeogene mass extinction
16. The end-Ordovician mass extinction
17. The Late Devonian crisis
18. The end-Triassic mass extinction
19. The end-Ordovician mass extinction
20. Mass extinction
21. The end-Permian mass extinction
22. International Commission on Stratigraphy
23. Global Boundary Stratotype Section and Point
24. The end-Ordovician mass extinction
25. The Late Devonian crisis
26. The numerical age of the Cambrian base is revised to 538.8 Ma
27. Evidence
28. Supports the stage and period boundary ages used throughout this pack, including the Cambrian base at 538.8 ± 0.2 Ma on recent editions against 541.0 ± 1.0 Ma on earlier ones. V55 verification basis: this session had no network access to any source — WebFetch was egress-blocked and the WebSearch budget was exhausted — so the cited work was not retrieved and its pagination was not re-checked. No chart edition was opened, so the boundary figures are quoted from standing knowledge of the chart rather than read from it, and the edition in which the Cambrian base changed is not identified.
29. Supports the general Precambrian narrative used here: stromatolite biogenicity reasoning, banded iron formation requirements, endosymbiotic origin of organelles and the framing of mass extinction as a measurement problem. Published in 2003, so it predates the 2016, 2018 and 2024 results also cited in this pack. V55 verification basis: this session had no network access to any source — WebFetch was egress-blocked and the WebSearch budget was exhausted — so the cited work was not retrieved and its pagination was not re-checked.