Geochemistry

The geochemistry ( ancient Greek γῆ ge 'earth', γεω -geo, earth concerning ' and χημεία chemeia, chemistry ') is concerned with the material construction of the distribution, the stability and circulation of chemical elements and their isotopes in minerals, rocks, soil, water, atmosphere and biosphere. It is the scientific discipline that combines geology and chemistry. She has in common with the geology of the subject matter and the chemistry of the methods of investigation.

History

Until the late 19th century, a descriptive approach was used in the geosciences, not or hardly the material basis and the chemical dynamics sought to understand the rocks and minerals according to their external characteristics, however, but with included. However, an understanding of these dynamics is essential, as many questions can be answered only by geochemical approaches.

Included the history of modern geochemistry, whose founders Victor Moritz Goldschmidt, Vladimir Ivanovich Vernadsky, Frank Wigglesworth Clarke and Alfred Treibs the early to mid 20th century, is thus closely linked with that of geology and mineralogy. The term itself goes back to the Swiss chemist Christian Friedrich Schönbein (1838 ). The most important stages on the way to the modern understanding of geochemistry presented the work of Carl Gustav Bischof ( 1846), Justus Roth ( 1818-1892; 1859) and James David Forbes ( 1868) dar.

Object of investigation

In the modern geochemistry, a division of the subject being observed. On the one hand, the investigation is metamorphic and igneous rocks, where the emphasis is on their trace element contents and (mostly radiogenic ) isotope ratios is to be able to make statements about age ( geochronology ) and formation conditions ( geothermobarometry ) with the goal. In the reconstruction of the earliest geological area, there are overlaps with the Planetary Science and Cosmochemistry. On the other hand there is the study of sediments, waters, soils, organisms and the air, the investigation of stable isotopes and the speciation of elements plays a prominent role. At this end of the spectrum of Geochemistry forms biogeochemistry, ie the investigation of the influence of organisms on the chemistry of the earth, the transition to biochemistry and biology.

Methods of investigation

For the analysis of liquid samples for the determination of the main elements of times the ion chromatography, ICP- OES and for ultra-trace elements using ICP- MS for trace elements. With the latter, the various isotopes may be measured. By coupling with a laser and solid samples can be studied with the latter sample, the laser removes material from the sample surface. Another way to measure the chemical composition of solid samples directly, the electron probe microanalysis. Often solid samples are also subjected to digestion and either melted or dissolved. The solidified melt tablet can then be examined by X-ray fluorescence analysis, while the entire bandwidth of the above methods are available for solutions.

In addition these standard methods other methods for specific issues exist: Mössbauer spectroscopy to distinguish between divalent and trivalent iron, the electron spin resonance for the detection of low concentrations of paramagnetic ions in minerals, the X-ray absorption spectroscopy and atomic force microscopy for chemical analysis of surfaces, the Raman spectroscopy and the infra-red spectroscopy for the detection of certain bonds and the elements involved in them as well as neutron activation analysis of extremely low concentrations.

Applications

• Geochemistry of the lithosphere

The contents and the distribution of elements in a mineral provide information about the history of the rock, including the pressure and temperature conditions at the time of formation ( geothermobarometry ). Many classifications of rocks based on geochemical data. Examples include the TAS diagram (total alkali silica) for glassy volcanic rocks and the subdivision of granites in S-type granites and I-type granites. Very often the concentration of the lanthanides are used to determine the development conditions and the classification of rocks.

• Geochemistry of hydrosphere

The Hydrogeochemistry investigated the water quality of surface and ground water, the water cycle and the interaction of water with minerals.

• Geochemistry of the Earth's atmosphere

Important issues of atmospheric chemistry are the greenhouse effect, the fine particulate air pollution and acid rain.

• Isotope Geochemistry

Stable isotopes provide information about areas of education, weathering processes and transport processes of rocks, ores and waters, radiogenic isotopes allow for age determination of minerals and rocks ( geochronology ).

• Cosmochemistry

The study of meteorites provides information on the origin of the universe, the solar system and the Earth.

Courses

Fundamentals of Geochemistry be taught in many geoscience bachelor's degree programs (eg " Earth Sciences ", " Geology / Mineralogy "). In-depth knowledge can in the Master's program " Earth Materials and Geochemistry " or can be purchased in geochemical depressions usually mineralogically oriented courses.