Revision summary
Fission-track dating counts damage trails from uranium-238 fission in minerals or glass. Price, Walker and Fleischer developed the method. Zircon, apatite and volcanic glass are the usual materials. Applications include dating tephra at hominin sites, heated stone, and Himalayan or Siwalik thermal history. Heat can anneal tracks and reset the clock, so dates need stratigraphic and other radiometric checks. Different minerals do not share one single year-range.
Model answer
Introduction
Fission-track dating is a radiometric clock that counts damage trails left when uranium-238 atoms split inside a mineral or glass. P. B. Price, R. M. Walker and R. L. Fleischer developed the method. For anthropology it is a way to date volcanic layers and heated materials that sit with fossils or tools.
Body
How the clock works
Uranium-238 occasionally undergoes spontaneous fission. Each fission leaves a tiny track in the crystal. The sample is polished and etched so the tracks can be counted under a microscope. The uranium content is measured, often by inducing extra tracks in a reactor. Age is then a function of track density and uranium concentration.
Useful materials include zircon, apatite and volcanic glass (obsidian or tephra). The method works over a wide geological span, from relatively young volcanic glasses to much older crustal minerals. The range depends on the mineral and on whether tracks have been reset by heat.
Heat can reset as well as date. Heating can anneal old tracks and restart the clock, which is why the method also records thermal history, not only “the age of the rock”.
Applications
- Hominin and Palaeolithic sites: Volcanic ash and tuff above or below fossils can be dated, alongside potassium–argon and argon–argon where those apply. East African rift volcanics are a standard setting.
- Obsidian and burnt flint: Provenance and last-heating events can be approached where tracks and chemistry allow.
- Siwaliks and mountain belts: Fission-track work on apatite and zircon is widely used in Himalayan cooling and uplift histories. That geological clock matters when we place Siwalik apes such as Sivapithecus in a landscape that was itself rising.
- Thermochronology: Even when the “age” is not an occupation date, the thermal path of a basin or a tool-stone source is anthropological context.
Limitation
Tracks fade if the mineral is heated above a closure temperature. Mixed ages and partial annealing need specialist interpretation. Fission-track dates should be cross-checked with stratigraphy and, where possible, with another radiometric method.
Flow diagram
flowchart TD U[Uranium-238 fission] --> T[Tracks in mineral] T --> A[Age from density plus U content] A --> V[Volcanic layers with fossils] A --> H[Himalayan cooling / Siwaliks]
Conclusion
Fission tracks count uranium fission damage in zircon, apatite or volcanic glass. Anthropology uses them for volcanic layers, heated stone and landscape history. Heat can reset the clock, so the date is never a slogan.
Quick related
Students also ask
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Mitochondrial DNA and human evolution.
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Is this the same as carbon-14?
No. Radiocarbon dates organic carbon on a shorter recent timescale. Fission tracks date uranium-bearing minerals and glasses, often much older volcanic or geological events.
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How does this relate to Siwalik apes?
Landscape clocks and volcanic clocks place fossils in time. Himalayan fission-track cooling is geological context for Sivapithecus.
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