Argon argon dating limitations

To obtain the content ratio of isotopes in a rock or mineral, the amount of Ar is measured by mass spectrometry of the gases released when a rock sample is melted in vacuum.The potassium is quantified by flame photometry or atomic absorption spectroscopy.K has a half-life of 1.248 billion years, which makes it eminently suitable for dating rocks.Potassium is chemically incorporated into common minerals, notably hornblende, biotite and potassium feldspar, which are component minerals of igneous rocks.After the recrystallization of magma, more being the most abundant isotope.Thus, the amount of calcium originally present is not known and can vary enough to confound measurements of the small increases produced by radioactive decay.

If the mineral composition of the two sample is different, so that the sample for measuring the potassium is richer or poorer in potassium than the sample used for measuring the argon, then this will be a source of error.Due to the long half-life, the technique is most applicable for dating minerals and rocks more than 100,000 years old.For shorter timescales, it is unlikely that enough Although it finds the most utility in geological applications, it plays an important role in archaeology.Another concern with K-Ar dating is that it relies on there being no Ar in the rock when it was originally formed, or added to it between its formation and our application of the K-Ar method.Because argon is inert, it cannot be chemically incorporated in the minerals when they are formed, but it can be physically trapped in the rocks either during or after formation. If the source of this argon is atmospheric contamination, then we can correct for this.

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