<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="1489" name="lanthanide series elements" parent="1426"/><uf><usefor name="lanthanoid elements"/></uf><bt><term thcode="2" code="1426" name="chemical element groups" parent="1382" scope="Groups shown at &lt;http://periodic.lanl.gov/&gt;"/><term thcode="2" code="1382" name="elements" parent="1174" scope="Chemical elements and element groups"/><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><rt><term thcode="2" code="1423" name="cerium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Ce and atomic number 58 &lt;http://periodic.lanl.gov/58.shtml&gt;"/><term thcode="2" code="1444" name="dysprosium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Dy and atomic number 66 &lt;http://periodic.lanl.gov/66.shtml&gt;"/><term thcode="2" code="1447" name="erbium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Er and atomic number 68 &lt;http://periodic.lanl.gov/68.shtml&gt;"/><term thcode="2" code="1450" name="europium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Eu and atomic number 63 &lt;http://periodic.lanl.gov/63.shtml&gt;"/><term thcode="2" code="1459" name="gadolinium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Gd and atomic number 64 &lt;http://periodic.lanl.gov/64.shtml&gt;"/><term thcode="2" code="1474" name="holmium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Ho and atomic number 67 &lt;http://periodic.lanl.gov/67.shtml&gt;"/><term thcode="2" code="1490" name="lanthanum" parent="1427" scope="Rare earth (lanthanide series) element with symbol La and atomic number 57 &lt;http://periodic.lanl.gov/57.shtml&gt;"/><term thcode="2" code="1497" name="lutetium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Lu and atomic number 71 &lt;http://periodic.lanl.gov/71.shtml&gt;"/><term thcode="2" code="1516" name="neodymium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Nd and atomic number 60 &lt;http://periodic.lanl.gov/60.shtml&gt;"/><term thcode="2" code="1545" name="praseodymium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Pr and atomic number 59 &lt;http://periodic.lanl.gov/59.shtml&gt;"/><term thcode="2" code="1546" name="promethium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Pm and atomic number 61 &lt;http://periodic.lanl.gov/61.shtml&gt;"/><term thcode="2" code="1553" name="rare earth elements" parent="1426" scope="A group of elements including the lanthanoids, or lanthanides, of interest because they are used in modern technological industries.  Yttrium and scandium are often included in this group."/><term thcode="2" code="1566" name="samarium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Sm and atomic number 62 &lt;http://periodic.lanl.gov/62.shtml&gt;"/><term thcode="2" code="1590" name="terbium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Tb and atomic number 65 &lt;http://periodic.lanl.gov/65.shtml&gt;"/><term thcode="2" code="1594" name="thulium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Tm and atomic number 69 &lt;http://periodic.lanl.gov/69.shtml&gt;"/><term thcode="2" code="1616" name="ytterbium" parent="1427" scope="Rare earth (lanthanide series) element with symbol Yb and atomic number 70 &lt;http://periodic.lanl.gov/70.shtml&gt;"/></rt></descriptor>