This principle presumes that the oldest layer of a stratigraphic sequence will be on the bottom and the most recent, or youngest, will be on the top.
The earliest-known hominids in East Africa are often found in very specific stratigraphic contexts that have implications for their relative dating.
When the electrode is placed in a solution that contains fluoride, it produces a voltage that is proportional to the amount of fluoride in the solution.
A calibration curve can be produced by measuring standard solutions of known fluoride concentration.
Radioactive carbon has a half-life of approximately 5,730 years which means that every 5,730 years, half of the carbon-14 will have decayed.Older specimens have higher fluoride contents than younger ones when burial conditions are identical.The requirement of identical burial conditions means that fluoride dating works best when it is applied within a single site with little variation in soil chemistry.The most common relative dating method is stratigraphy.Other methods include fluorine dating, nitrogen dating, association with bones of extinct fauna, association with certain pollen profiles, association with geological features such as beaches, terraces and river meanders, and the establishment of cultural seriations.