Absolute dating rocks

21-Jul-2017 10:42

Development of this process was aided by German chemists Otto Hahn and Fritz Strassmann, who later went on to discover nuclear fission in December 1938.The utility of the rubidium–strontium isotope system results from the fact that Sr with a half-life of 48.8 billion years.This is well known for the Cenozoic time-scale but, due to poorer preservation of carbonate sequences in the Mesozoic and earlier, it is not completely understood for older sequences.In older sequences diagenetic alteration combined with greater uncertainties in estimating absolute ages due to lack of overlap between other geochronometers (for example U–Th) leads to greater uncertainties in the exact shape of the Sr isotope seawater curve.

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These printables describe the rock cycle, the different types of rocks, and the ways people use rocks and minerals.Each of these minerals has a different initial rubidium/strontium ratio dependent on their potassium content, the concentration of Rb and K in the melt and the temperature at which the minerals formed.Rubidium substitutes for potassium within the lattice of minerals at a rate proportional to its concentration within the melt.The ideal scenario according to Bowen's reaction series would see a granite melt begin crystallizing a cumulate assemblage of plagioclase and hornblende (i.e.; tonalite or diorite), which is low in K (and hence Rb) but high in Sr (as this substitutes for Ca), which proportionally enriches the melt in K and Rb.

This then causes orthoclase and biotite, both K rich minerals into which Rb can substitute, to precipitate.Although this is a potential source of error for terrestrial rocks, it is irrelevant for lunar rocks and meteorites, as there are no chemical weathering reactions in those environments.

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