Dates above and below a location provide minimum and maximum age determinations according to the law of superimposition.
These grains absorb radiation over time from the surrounding sediments and the radiation (electrons) remain trapped within the mineral grain structure.
When the grain is exposed to intense light of particular wavelengths in the laboratory, it emits a light signal with an intensity proportional to the radiation it has absorbed while buried.
The measurement is based on an isotope of potassium that radioactively decays at a known rate into argon.
K-Ar dating has been used to date lava flows above and below archaeological deposits that contain important hominid fossils in Africa's Olduvai Gorge.
A number of methods are used, all of which have their advantages, limitations and level of accuracy.
Complex dating problems often use a variety of techniques and information to arrive at the best answer.
This technique can determine ages between a few hundred years to more than 100,000 years.
It has been used at Willandra to date the layers above and below the location of Mungo Lady and Mungo Man , and the layers above and below the footprints horizon.
Working out how old archaeological remains are is a vital part of archaeology.
Scientific dating has confirmed the long residence of Aboriginal people in Australia.
This 'law of superimposition' works in the well-defined layers of the Willandra lunettes, but only dates objects as younger or older than adjacent layers.