Zircon as a geochronometer

Assembled from 9 blocks · 1 evidence · 6 related

1. Story
2. Zircon (ZrSiO4) is the mineral that makes deep time measurable to four significant figures, and it does so because of a lattice accident. Uranium substitutes readily for zirconium when the crystal grows; lead does not fit at all. A newly crystallised zircon therefore contains uranium and effectively no lead, so essentially every lead atom found in it later was made in place by decay — the initial-daughter correction that limits most other systems largely disappears. Zircon is also mechanically and chemically tough, surviving erosion, transport, burial and even partial melting, which is why the oldest known fragment of Earth is a detrital zircon from the Jack Hills of Western Australia dated to about 4.4 billion years rather than a rock. The residual problem is lead loss from radiation-damaged domains, and the standard remedy is chemical abrasion: partially dissolve the damaged parts away before analysis and date only what survives. That single procedural change, introduced in the mid-2000s, is most of the reason a boundary age can now carry an uncertainty of a few tens of thousands of years.
3. Knowledge
4. Zircon as a geochronometer
5. Connections
6. Radiometric dating
7. The end-Permian extinction is resolved to about sixty thousand years
8. Evidence
9. 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.