Dating quaternary events by luminescence

The exposure to radioactive elements continues, and the minerals begin again storing free electrons in their structures.

If you can measure the rate of acquisition of the stored energy, you can figure out how long it has been since the exposure happened.

Electrons from these substances get trapped in the mineral's crystalline structure, and continuing exposure of the rocks to these elements over time leads to predictable increases in the number of electrons caught in the matrices.

But when the rock is exposed to high enough levels of heat or light, that exposure causes vibrations in the mineral lattices and the trapped electrons are freed.

Thermoluminescence was first clearly described in a paper presented to the Royal Society (of Britain) in 1663, by Robert Boyle, who described the effect in a diamond which had been warmed to body temperature.

The possibility of making use of TL stored in a mineral or pottery sample was first proposed by chemist Farrington Daniels in the 1950s. Applications and limitations of thermoluminescence to date quaternary sediments.

Better still, unlike radiocarbon dating, the effect luminescence dating measures increases with time.

In the same way, more or less, OSL (optically stimulated luminescence) dating measures the last time an object was exposed to sunlight.

Artifacts which can be dated using these methods include ceramics, burned lithics, burned bricks and soil from hearths (TL), and unburned stone surfaces that were exposed to light and then buried (OSL).

Geologists have used OSL and TL to establish long, log chronologies of landscapes; luminescence dating is a powerful tool to help date sentiments dated to the Quaternary and much earlier periods. The potential of using thermoluminescence to date buried soils developed on colluvial and fluvial sediments from Utah and Colorado, U.

Two forms of luminescence dating are used by archaeologists to date events in the past: thermoluminescence (TL) or thermally stimulated luminescence (TSL), which measures energy emitted after an object has been exposed to temperatures between 400 and 500°C; and optically stimulated luminescence (OSL), which measures energy emitted after an object has been exposed to daylight.

To put it simply, certain minerals (quartz, feldspar, and calcite), store energy from the sun at a known rate.

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