Relative and chronometric dating
The of a fossil bone is determined by comparison of the chemical composition with that of other fossil bones of known ages.
These include soil concentration and length of burial.
This shows also contemporaneity of hominid bones and animal bones buried at the same site.
After death the radioactive C14 is not replenished from the atmosphere. The quantity is halved after 5,570 years which is the .
The of a skull or mandible is usually obtained indirectly when it comes from a deposit containing more suitable for radiocarbon dating.
This is because the C14 content is too small then to estimate.
It is convenient to assess the residual organic matter in fossil bone or dentine by determination of the nitrogen content.
Over the passage of time bones and teeth in permeable deposits progressively accumulate fluorine.Nitrogen decreases in buried bone and affects nitrogen concentrations. With regard to relative dating Comparative geology includes correlations with soil pollen content.Therefore nitrogen disappears rapidly under and may be absent. Studies of the fossil fauna assemblage, comparison with other sites, and the different layers at the same site.These are leached out or retained according to local conditions. Alteration of the phosphatic material of which bones are mainly composed is hydroxyapatite.The addition of new mineral matter, such as lime or iron oxide, changes the latter and leads to an increase in weight.Contemporaneity is not always justifiable due to mankind’s long established practices of burying the dead.