<?xml version="1.0" encoding="utf-8"?><!DOCTYPE Zthes SYSTEM "http://zthes.z3950.org/xml/zthes-05.dtd">  <Zthes><term><termId>31341244</termId><termName>cation-ratio dating</termName><termType>PT</termType><termNote><![CDATA[ Cation-ratio dating involves the analysis of biogenic rock varnish, a micrometer-thick coating of manganese, silicon, aluminum and iron, believed to age predictably and thus serve as a chronometer. In particular, the ratio of certain cations, (calcium + potassium)/titanium, has been posited to decrease as the varnish ages. In recent decades, some scholars have challenged these assumptions and questioned the usefulness of the technique as a reliable way to date lithic artifacts.  ]]></termNote><termCreatedDate>2026-03-30 20:32:02</termCreatedDate><relation><relationType>UF</relationType><termId>31341245</termId><termName>dating, cation-ratio</termName><termType>ND</termType></relation><relation><relationType>BT</relationType><termId>31317179</termId><termName>dating</termName><termType>PT</termType></relation></term>  </Zthes>