{"thcode":2,"term":{"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."},"uf":[],"bt":[{"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."},{"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":[],"rt":[{"code":668,"name":"lithostratigraphy","parent":1104,"scope":"Branch of stratigraphy dealing with the study of units of rock. Each unit is composed of a body of rock which is dominated by a certain lithology or similar color, mineralogic composition, and grain size."}]}