A number of methods are used, all of which have their advantages, limitations and level of accuracy.

principle of carbon dating-32

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Potassium-argon (K-Ar) dating is a radiometric technique that is used to determine the age of minerals that contain potassium, which include clay minerals and micas.

It is most useful for minerals older than 100,000 years and can reach way back into the geological past.

It uses the fact that natural carbon contains a known ratio of ordinary carbon and the radioactive isotope carbon-14, and that this mix is reflected in carbon taken up by living organic materials such as wood, shells and bones.

When organisms die, the carbon-14 begins to decay at a known rate.

Artefacts and other materials can be dated in relative terms by observing which layer of sediments they are found in.

This applies the geological principle that under normal circumstances younger layers of sediment will be deposited on top of older layers.

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.

For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built.

Similarly, in geology, if distinctive granitic pebbles can be found in the sediment beside a similar granitic body, it can be inferred that the granite, after cooling, had been uplifted and eroded and therefore was not injected into the adjacent rock sequence.

Dates above and below a location provide minimum and maximum age determinations according to the law of superimposition.