{"thcode":2,"term":{"code":1680,"name":"age estimation methods","parent":619,"scope":"Methods used to determine the age of earth materials, typically by laboratory analysis of properties of those materials."},"uf":[{"name":"dating methods","usewith":false}],"bt":[{"code":619,"name":"laboratory methods","parent":734,"scope":"Techniques to analyze and test samples in a place equipped and designed for the work."},{"code":734,"name":"methods","parent":1,"scope":"Techniques, methods, procedures, or strategies for research, management, collection, or analysis of scientific information in USGS."},{"code":1,"name":"Categories","parent":null,"scope":"Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."}],"nt":[{"code":393,"name":"fission-track dating","parent":1680,"scope":"Laboratory technique for determining the age of rocks and other geological materials by counts of spontaneous and induced fission tracks left by the radioactive isotope uranium-238."},{"code":1677,"name":"luminescence dating","parent":1680,"scope":"Dating methods that involve the analysis of the optical properties of minerals exposed to environmental radiation.  Typically used to determine the age of subaerial exposure of surficial sediments."},{"code":1713,"name":"sclerochronology","parent":1680,"scope":"Description of the history of individual organisms by studying the variations in thickness of accretionary layers in their skeletons."},{"code":1681,"name":"tephrochronology","parent":1680,"scope":"Age determination of rocks and deposits by correlation of volcanic ash layers (tephra) that bound the deposits below and above."}],"rt":[{"code":954,"name":"radiometric dating","parent":609,"scope":"Methods for age determination of rocks and fossils by measuring the proportions of naturally occurring radioactive isotopes to their decay products."},{"code":1188,"name":"tree ring analysis","parent":619,"scope":"Study of the variations in width and number of tree rings to date historical events and to study periods of climatic and hydrologic changes."}]}