Electron Spin Resonance Dating

Tooth enamel is preferable because it is more mineralogical, contains fewer organic components that can undergo postmortem alteration, and has simpler uranium uptake kinetics. Dentin is more susceptible to chemical alteration after burial, which can complicate dose-rate estimates and increase measurement uncertainty.

Uranium from surrounding sediment can migrate into bones and teeth after burial, gradually increasing their uranium content. This affects the radiation dose the sample receives over time. ESR age estimates depend on knowing the uranium uptake history. Different models (linear, early, or no uptake) produce different ages. Careful uranium measurements at different sample depths can help constrain the true uptake pattern.

The ESR spectrum plots microwave absorption versus magnetic field strength, typically showing multiple peaks corresponding to different paramagnetic defect centers. The intensity (peak height or integrated area) of the most prominent peak is proportional to the number of trapped electrons. This intensity is measured relative to a standard and compared to laboratory irradiation curves to estimate paleodose.

In principle, ESR can date older materials, but signal saturation is a practical limitation. At very high radiation doses, the number of available traps becomes depleted, and the relationship between dose and signal becomes non-linear. This causes apparent ages to plateau. Some minerals and special protocols (e.g., deep traps) extend the range, but ages beyond ~1 Myr are uncertain.

Bones are susceptible to postmortem alteration and uranium uptake, making them less reliable. Tooth enamel is superior because it is dense and resistant to alteration. Shells can be dated but have their own complications with uranium uptake. Sediments (especially heated quartz) are ideal because they have closed systems, but organic archaeological materials like bone and tooth are the most common targets in paleontology.