<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="1367" name="earth material properties" parent="287" scope="Physical characteristics of rocks and unconsolidated earth materials such as soils and sediments."/><bt><term thcode="2" code="287" name="earth characteristics" parent="1174" scope="The measurable, definable properties and features of the earth."/><term thcode="2" code="1174" name="topics" parent="1" scope="Themes, subjects, and concerns for which USGS information resources are relevant."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><nt><term thcode="2" code="2276" name="acid neutralizing potential" parent="1367" scope="Geochemical capacity of earth materials to affect the pH of waters flowing through them."/><term thcode="2" code="1714" name="bulk density" parent="1367" scope="Overall density of an unconsolidated earth material."/><term thcode="2" code="2290" name="electromagnetic reflectance and emissivity" parent="1367" scope="Effectiveness of an earth material in reflecting or emitting radiation, varying by wavelength.  Measurements are made over the infrared part of the electromagnetic spectrum in a laboratory to compare with remotely-sensed data obtained by airborne or satellite imaging systems."/><term thcode="2" code="1741" name="magnetism" parent="1367" scope="Strength and orientation of the permanent magnetic field in a given sample of an earth material"/><term thcode="2" code="1368" name="permeability" parent="1367" scope="The ability of fluids to pass through an earth material, typically depending on the connectedness of pore space in the material."/><term thcode="2" code="1369" name="porosity" parent="1367" scope="The proportion of open space in a rock or unconsolidated material."/><term thcode="2" code="1701" name="radioactivity" parent="1367" scope="Release of subatomic particles from earth materials.  Generally the energy of these particles is used to determine the chemical elements present."/><term thcode="2" code="1712" name="resistivity" parent="1367" scope="Electrical resistance of materials, often measured in boreholes."/><term thcode="2" code="2027" name="soil moisture" parent="1367" scope="Water content of soil and other near-surface unconsolidated earth material"/><term thcode="2" code="2028" name="soil temperature" parent="1367" scope="Temperature and temperature gradients in soil and other near-surface unconsolidated earth materials"/></nt><rt><term thcode="2" code="2279" name="thermal maturation" parent="435" scope="Chemical alteration of organic material within sediments and sedimentary rocks as a result of heat. Measures of thermal maturation indicate the extent of transformation of detrital organic material into coal and petroleum."/></rt></descriptor>