New dating methods: luminescense (Introduction)

by David Turell , Saturday, October 14, 2017, 19:58 (2598 days ago) @ David Turell

Mentioned in passing in the previous entry. This is an expanded explanation:

https://cosmosmagazine.com/archaeology/kira-westaway-the-woman-who-dates-hobbits-and-gi...

"She followed her first degree with a masters in quaternary science at Royal Holloway, part of the University of London. It was there that she discovered luminescence dating.

"This measures the amount of light that shines from minerals such as quartz and feldspar when they’re heated or illuminated. The brightness of the emitted light determines when the sample was last heated or exposed to sunlight.

"Consider a grain of quartz on the ground. Over time, electrons energised by the decay of cosmic uranium, potassium and thorium isotopes become lodged in the quartz crystal lattice. When the grain is exposed to sunlight, that energy vibrates the lattice, releasing the electrons in a burst of light and “resetting” the clock to zero.

"But if the quartz is washed into a cave by a stream, or blown in by wind and buried, it continues to accumulate electrons without being “reset”. The longer the grain is buried, the more electrons it collects and the brighter it glows when it is dug up by archaeologists and exposed to light again in a laboratory.

"This is the underlying principle of optically stimulated luminescence dating. Thermally stimulated luminescence dating is similar, but measures the last time the sample was heated to around 400 to 500 °C.

"Luminescence dating is often used in concert with radioisotope dating, which relies on comparing the ratio of isotopes in a sample to nut out how old it is. Carbon dating, for instance, measures the amount of carbon-14 in a sample, which decays by half every 5,730 years. After around 50,000 years, there’s very little carbon-14 left to detect.

"This is where luminescence really shines: it can measure up to hundreds of thousands of years. This means it is much more useful for dating artefacts and bones from the Quaternary era, which roughly marks the emergence of our earliest Homo ancestors.

"Say you find a stone tool in an archaeological dig, Westaway says. Without knowing how old it is, you can’t say much about it. But using luminescence dating, you could find out when it and its surrounding sediment was buried. “Suddenly you put an age to the stone tool and it could be the oldest stone tool on the continent, or the first evidence that humans were making tools.

“'Dating just puts that context, that meaning, on it. It really is a huge game-changer.'”

Comment: This method is said to be accurate for several hundred thousand years. Not millions. But it does cover H. sapiens time on Earth. I hope Tony might comment.