Global Boundary Stratotype Section and Point

Assembled from 16 blocks · 1 evidence · 9 related

1. Story
2. A GSSP — the "golden spike" — is a physical point in a physical outcrop that defines the base of a geological stage for the whole planet. The distinction that matters is between definition and measurement: the boundary IS the marker horizon in that section, usually the first appearance of a chosen fossil species, and the numerical age attached to it is a separate, revisable measurement of that same horizon. This is why a boundary can be redated without being moved. It also explains an oddity readers often trip on — the base of the Cambrian is defined by the first appearance of a burrow, the trace fossil Treptichnus pedum, rather than by any of the animals the Cambrian is famous for, because a definition must be recognisable in ordinary rock rather than only in exceptional deposits. GSSPs are ratified by the International Commission on Stratigraphy and subsequently by the International Union of Geological Sciences; the majority of Phanerozoic stages now have one, while Precambrian boundaries are still mostly defined by agreed numerical ages instead.
3. Knowledge
4. Global Boundary Stratotype Section and Point
5. International Commission on Stratigraphy
6. Connections
7. International Commission on Stratigraphy
8. Fortune Head GSSP, Newfoundland
9. Meishan GSSP, Changxing, Zhejiang
10. The numerical age of the Cambrian base is revised to 538.8 Ma
11. Global Boundary Stratotype Section and Point
12. The end-Ordovician mass extinction
13. The Late Devonian crisis
14. The numerical age of the Cambrian base is revised to 538.8 Ma
15. Evidence
16. 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.