Dating techniques used in archaeology
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.
It is most useful for minerals older than 100,000 years and can reach way back into the geological past.
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.
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.
Search for dating techniques used in archaeology:
This has to be done slowly and painstakingly, and the archaeologists will record and preserve anything found at every stage and depth (for example paint flakes, hair, clothing or DNA) as it may be vital evidence.