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Iscochron dating is a type of radiometric dating. Radiometric dating observes the ratio of parent to daughter products, generally in circumstances where the daughter product is an isotope of the parent and hence has the same chemical properties.
The best known of such simple radiometric methods is carbon dating, a method that by its nature is particularly reliable (over a limited time span) owing to the known isotope ratios when substances such as wood (a form of cellulose) are formed by incorporation and transformation of atmospheric carbon dioxide, which has a constant ratio of carbon isotopes owing to unstable carbon 14 isotope formation by neutrons freed by the impact of cosmic rays. This carbon 14 is subsequently degraded by radioactive decay back to nitrogen at a predictable rate.
When the daughter product(s) of the parent are not isotopes, but instead have differing chemical properties substantial complexities are introduced. This is because a cooling mineral may differentiate into various crystal species, forming a matrix. (An example of this differentiation process is seen in granites, which appear typically gray but which upon close examination are seen to be a matrix of white quartz, black feldspar and several other minerals.) Isochron dating is a method of determining the age of certain differentiated rocks since solidification. It has the advantage of allowing for the differential migration of parent/daughter components into the various minerals comprising the matrix. If some of the differentiated minerals may be selectively lost or gained (for example, if one is more soluble in water), this must be taken into account in the analysis.
Isochron dating is useful in the determination of the age of igneous rocks, which have their initial origin in the cooling of liquid magma from volcanos. This in turn can reveal information about the motions of continents due to plate tectonics and the dates of large asteroid impacts upon the earth.
See also
External links
Isochron dating site (http://www.talkorigins.org/faqs/isochron-dating.html)
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