Radiometric dating

Assembled from 25 blocks · 2 evidence · 15 related

1. Story
2. The family of techniques that convert a measured ratio of parent to daughter isotope in a mineral into an absolute age, using a decay constant determined in the laboratory. The workhorse of deep time is uranium–lead in zircon, and its power comes from redundancy rather than from any single measurement: uranium-238 decays to lead-206 with a half-life near 4.47 billion years while uranium-235 decays to lead-207 with a half-life near 0.70 billion years, so one crystal carries two independent clocks that must agree. Where they disagree, the crystal has leaked, and the disagreement is itself the diagnostic. Argon-40/argon-39 on sanidine gives a second, chemically unrelated system; reconciling the two required an explicit intercalibration of decay constants and standard ages, which is why boundary ages shifted slightly in the early 2010s without any new rock being collected. The critical point for a reader is that a radiometric age dates the crystallisation of a mineral, not the death of an organism — a fossil is dated by bracketing it between datable volcanic ash beds above and below.
3. Knowledge
4. Radiometric dating
5. Zircon as a geochronometer
6. Mass extinction
7. Connections
8. Mass extinction
9. Zircon as a geochronometer
10. Molecular clock dating
11. The end-Permian mass extinction
12. Sulfur mass-independent fractionation is proposed as an atmospheric oxygen proxy
13. The K–Pg boundary is dated to 66.043 ± 0.043 Ma
14. The end-Permian extinction is resolved to about sixty thousand years
15. Radiometric dating
16. The end-Permian mass extinction
17. The Cretaceous–Palaeogene mass extinction
18. The end-Ordovician mass extinction
19. The Late Devonian crisis
20. The end-Triassic mass extinction
21. Radiometric dating
22. The end-Permian extinction is resolved to about sixty thousand years
23. Evidence
24. Supports the Permian–Triassic boundary age of 251.902 ± 0.024 Ma from Meishan zircons and the constraint of the main extinction pulse to roughly sixty thousand years. 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. Volume and page range are quoted from standing knowledge and were not re-checked.
25. Supports the boundary age of 66.043 ± 0.043 Ma and the finding that the Chicxulub impact and the extinction horizon are indistinguishable in time. 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. Volume and page range are quoted from standing knowledge and were not re-checked.