geochemistry


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Schematic representation of a geochemical cycle

The geochemistry ( Greek γεω- geo- , the Earth concerning '[to γῆ ge ' earth '], and chemistry ) is a branch of chemistry that deals with the material construction of the distribution, stability and the cycle of chemical elements and their isotopes in minerals , rocks , soil , water , earth's atmosphere and biosphere . It is the scientific discipline that combines geology and chemistry. It shares the object of investigation with geology and the investigation methods with chemistry.

history

Until the late 19th century, a descriptive approach was pursued in the geosciences, which sought to understand rocks and minerals according to their external properties, but did not or hardly included the material basis and their chemical dynamics. Understanding these dynamics is essential, however, because many questions can only be answered by geochemical approaches.

The history of modern geochemistry, of which Victor Moritz Goldschmidt , Wladimir Iwanowitsch Wernadski , Frank Wigglesworth Clarke and Alfred Treibs were among the founders in the early to mid-20th century, is therefore closely linked to that of geology and mineralogy . The term itself goes back to the Swiss chemist Christian Friedrich Schönbein (1838). The work of Karl Gustav Bischof (1846), Justus Roth (1818–1892; 1859) and James David Forbes (1868) represented important stages on the way to a modern understanding of geochemistry .

research object

In modern geochemistry, the subject is divided into two parts. On the one hand there is the investigation of metamorphic and igneous rocks, whereby the main focus is on their trace element content and (mostly radiogenic) isotope ratios, with the aim of being able to make statements about age ( geochronology ) and formation conditions ( geothermobarometry ). In the area of ​​the reconstruction of the earliest geological history, there is an overlap with planetology and cosmochemistry . On the other hand there is the investigation of sediments, water, soils, living beings and the air, with the investigation of stable isotopes and the speciation of elements playing a prominent role. At this end of the spectrum of geochemistry, biogeochemistry , i.e. the study of the influence of organisms on the chemistry of the earth, forms the transition to biochemistry and biology .

Investigation methods

For the analysis of liquid samples, ion exchange chromatography is often used to determine the main elements , optical emission spectrometry with inductively coupled plasma (ICP-OES) for trace elements and mass spectrometry with inductively coupled plasma (ICP-MS) for ultra- trace elements . The latter can also be used to measure the frequency of different isotopes in a sample. Through the coupling with a laser, solid samples can also be examined with the ICP-MS, with the laser removing material from the sample surface. Another way to measure the chemical composition of solid samples directly is electron beam microanalysis . Often solid samples are also subjected to a digestion and either melted or dissolved. The solidified orodispersible tablet can then be examined using X-ray fluorescence analysis, while the entire range of the above-mentioned methods is available for solutions.

In addition to these standard methods, there are other methods for special questions: Mössbauer spectroscopy to differentiate between divalent and trivalent iron , electron spin resonance for the detection of low concentrations of paramagnetic ions in minerals, X-ray absorption spectroscopy and atomic force microscopy for the chemical investigation of surfaces, Raman spectroscopy and infrared spectroscopy for Detection of certain bonds and the elements involved in them as well as the neutron activation analysis for extremely low concentrations.

Applications

courses

The basics of geochemistry are taught in many geoscientific bachelor's degree programs (e.g. "Geosciences", "Geology / Mineralogy"). In-depth knowledge can be acquired in the master’s degree in “Geomaterials and Geochemistry” or in geochemical specializations, mostly mineralogically oriented degree programs. In German university policy, geochemistry is classified as a minor subject ; it is recorded by the “Small Subjects Unit” together with mineralogy, petrology and similar fields.

literature

  • Allègre, CJ; Michard G .; Varney, RN: Introduction to Geochemistry. ISBN 90-277-0497-X
  • Faure, G. (1998): Principles and applications of geochemistry. 2nd Edition. Prentice Hall, New Jersey.
  • Levinson, AA (1980): Introduction to Exploration Geochemistry , Second Edition, Applied Publishing Ltd., ISBN 0-915834-04-9
  • Marshall, CP; Fairbridge, RW (1999): Encyclopedia of geochemistry. Encyclopedia of Earth Sciences Series. Springer-Verlag, ISBN 0-412-75500-9
  • Mason, B. & Moore, C. (1985): Principles of Geochemistry . 2nd Edition. Spectrum Academic Publishing House, ISBN 978-3-8274-1262-1
  • Matschullat, J .; Tobschall, HJ; Voigt, H.-J. (1997): Geochemistry and Environment. Springer-Verlag, Berlin, ISBN 3-540-61866-X
  • Schlesinger, WH (2005): Biogeochemistry . Vol. 8 in: Treatise on Geochemistry. Elsevier Science, ISBN 0-08-044642-6

Web links

Wiktionary: Geochemist  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Small subjects :Geochemistry on the Small Subjects portal. , accessed April 23, 2019