{"thcode":2,"term":{"code":437,"name":"geochemistry","parent":291,"scope":"Study of the distribution of chemical elements and natural compounds on the earth and in the atmosphere and the chemical processes that affect the earth."},"uf":[{"name":"chemistry (Earth sciences)","usewith":false},{"name":"geochemical anomaly maps","usewith":{"code":700,"name":"maps and atlases","parent":808,"scope":"Representation, usually on a flat surface, of a part or whole of the Earth or other parts of the universe.  Collections of maps linked digitally or bound together in a book are called atlases."}}],"bt":[{"code":291,"name":"earth sciences","parent":1019,"scope":"Broad term for all science related to the study of the earth."},{"code":1019,"name":"sciences","parent":1,"scope":"Major educational fields, fields of study, and professional groupings within 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":1078,"name":"soil chemistry","parent":437,"scope":"Branch of chemistry concerned with the elements and compounds that make up soils. Includes chemical processes involving soils."},{"code":1298,"name":"water chemistry","parent":437,"scope":"Branch of chemistry that deals with the elements and compounds in water."}],"rt":[{"code":69,"name":"atomic absorption analysis","parent":153,"scope":"Technique used to identify chemicals based on the measurement of the spectra produced by atoms and molecules with absorption of electromagnetic radiation."},{"code":93,"name":"biogeochemical cycling","parent":310,"scope":"The cycling of chemical constituents through a biological system."},{"code":141,"name":"carbon cycling","parent":93,"scope":"The circulation of carbon in the biosphere, atmosphere, and hydrosphere through a series of processes that include photosynthesis, consumption, and respiration."},{"code":142,"name":"carbon isotope analysis","parent":654,"scope":"Experimental determination of the proportion of a given stable carbon isotope (C12 or C13) in a sample."},{"code":153,"name":"chemical analysis","parent":619,"scope":"Chemical techniques used to identify the composition of substances."},{"code":158,"name":"chromatography","parent":153,"scope":"Analytical techniques used to separate or partition the components of a gaseous or liquid mixture by differences in absorption rates during flow around or over surface absorbents such as columns of silica, filter papers, or gels."},{"code":288,"name":"earth history","parent":455,"scope":"The structural and compositional changes that the earth has undergone from its formation. Use for discussions of the whole earth (or large sections of it) instead of regional studies."},{"code":426,"name":"gas chromatography","parent":158,"scope":"Chromatographic technique used to separate or partition the components of a mixture.  Solid and liquid samples are vaporized and passed through a column containing a liquid that differentially absorbs the  molecules."},{"code":435,"name":"geochemical processes","parent":101,"scope":"Processes affecting the amount, distribution, or structure of chemical elements in air, water, soil, rocks, and minerals."},{"code":609,"name":"isotopic analysis","parent":619,"scope":"Experimental determination of the proportion of a given isotope (or isotopes) in a sample."},{"code":654,"name":"light stable isotope analysis","parent":609,"scope":"Analytical technique using mass spectrometry to measure the different isotopic forms of low mass (light) elements such as oxygen, hydrogen, carbon, nitrogen and sulfur that occur in samples."},{"code":662,"name":"liquid chromatography","parent":158,"scope":"Chromatographic technique to separate or partition the components of a mixture in which samples are liquid and passed through a column."},{"code":711,"name":"mass spectroscopy","parent":153,"scope":"Instrumental technique to separate and identify molecules.  Gaseous ions are formed, with or without fragmentation.  Their mass\/charge ratios and relative electrical abundance are then measured or the spectra are recorded."},{"code":727,"name":"metamorphism (geological)","parent":451,"scope":"Process by which rocks are altered in composition and texture by extreme heat, high pressure, or the action of chemicals."},{"code":783,"name":"neutron activation analysis","parent":153,"scope":"Sensitive laboratory technique for both qualitative and quantitative analysis of elements in samples.  Target nuclei are bombarded with neutron beams to start nuclear reactions which emit characteristic gamma ray radiations."},{"code":855,"name":"oxygen isotope analysis","parent":654,"scope":"Experimental determination of the proportion of a given stable oxygen isotope in a sample."},{"code":872,"name":"particle-beam spectroscopy","parent":153,"scope":"Analytical technique using a concentrated beam of charged subatomic particles."},{"code":1191,"name":"tritium analysis","parent":654,"scope":"Mass spectrometric measurement of the decay of the radioactive isotope of hydrogen in water samples as a means of dating and investigating changes in water."}]}