# Infrared spectral library of tooth enamel from African ungulates for accurate electron spin resonance dating

## TL;DR

This paper creates an infrared spectral library for African ungulate tooth enamel to improve the accuracy of dating fossils using ESR/U-series methods.

## Contribution

The novel contribution is a reference infrared spectral library for African ungulate tooth enamel to assess diagenetic changes and improve dating accuracy.

## Key findings

- Infrared spectroscopy tracks diagenetic history of carbonate hydroxyapatite in tooth enamel.
- The library helps identify best-preserved specimens for accurate ESR/U-series dating.
- Uranium incorporation correlates with atomic order in carbonate hydroxyapatite crystals.

## Abstract

Electron spin resonance coupled with uranium-series dating (ESR/U-series) of carbonate hydroxyapatite in tooth enamel is the main technique used to obtain age determinations from Pleistocene fossils beyond the range of radiocarbon dating. This chronological information allows to better understand diachronic change in the palaeontological record, especially with regard to the evolution of the genus Homo. Given the relative paucity of human teeth at palaeontological and archaeological localities, ESR/U-series is widely applied to the teeth of ungulate species. However, the accuracy of ESR/U-series ages is greatly affected by the incorporation of uranium in the enamel during burial in sediments. It has been shown that uranium content is positively correlated with an increased degree of atomic order in carbonate hydroxyapatite crystals, the latter determined using infrared spectroscopy. Here we present a reference infrared spectral library of tooth enamel from African ungulates, based on the grinding curve method, which serves as baseline to track the diagenetic history of carbonate hydroxyapatite in different species and thus select the best-preserved specimens for dating.