palaeothermometer
/ˌpalɪəʊθəˈmɒmɪtə/ /ˌpeɪlɪəʊθəˈmɒmɪtə/Geology
noun
Any geological fact, measurement, or sample that may be used as a means of inferring palaeotemperatures, especially the relative abundance of the isotopes of certain chemical elements in fossil organic matter.
Origin
1940s. From palaeo- + thermometer.