Collagen is a protein abundant in living bone, which contains about 4% nitrogen. Collagen survives long after death and the collagen content of a bone, measured by the amount of nitrogen present, yields information as to its relative date. The rate of decay is varies with temperature and other aspects of the environment, but collagen dating can only give relative dates for different bone samples from a particular site. The test is used mainly in association with the fluorine test and radiometric assay, as in the cases of Piltdown and Swanscombe Man.