Dating Mammalian Tooth Enamel using 4He

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With National Science Foundation support Dr. Thure Cerling will examine the potential of measuring the concentration of 4He in fossil tooth enamel as a method for absolute age determination. 4He is a decay product of Uranium and if 4He is retained in the tooth, and no confounding variables are present, the amount should be time dependent. Preliminary work has yielded two very interesting results. First, there is no close relationship between the amounts of uranium and 4He present. Secondly, analysis of samples of known age indicates that the amount of 4He is very closely related to age. The cause of this apparent anomaly is not understood although Dr. Cerling postulates that although U is taken up in teeth after burial, the resultant 4He is not tightly bound into the matrix and is thus lost. He will attempt to illuminate the mechanisms of 4He production and loss. To accomplish this he will analyze teeth of known age from a number of sites with different sedimentological and temperature histories. He will measure the distribution of 4He as well as 3He within these samples. He will compare samples which give accurate vs. aberrant dates to determine if selection criteria can be established. Cross sections of teeth will be autoradiographed to determine the distribution of uranium. In order to understand the adsorption and solubility of uranium in enamel, leaching tests will also be conducted.This research is important because, if successful, it will lead to a dating technique of widespread use in paleoanthropology as well as geological and biological sciences.