Argon 40 dating

Susie Welch, recently retired outreach coordinator at the New Mexico Bureau of Geology, was recognized by Governor Susana Martinez for outstanding accomplishments and invaluable contributions to the state of New Mexico.

Congratulations to Susie on the well-deserved citation!

The site also must be geologically meaningful, clearly related to fossil-bearing rocks or other features that need a good date to join the big story.

By comparing the proportion of K-40 to Ar-40 in a sample of volcanic rock, and knowing the decay rate of K-40, the date that the rock formed can be determined.

Potassium (K) is one of the most abundant elements in the Earth's crust (2.4% by mass).

is a radiometric dating method invented to supersede potassium-argon (K-Ar) dating in accuracy.

Potassium-Argon Dating Potassium-Argon dating is the only viable technique for dating very old archaeological materials.

Common phases to be used for argon-argon dating are white micas, biotite, varieties of potassium feldspar (especially sanidine because it is potassium-rich), and varieties of amphibole. This can be used to solve equation 2 for the sample.

Second, the sample is irradiated along with a standard of a known age. A major advantage of the argon-argon method is that the sample can be heated incrementally.Potassium can be mobilized into or out of a rock or mineral through alteration processes.Due to the relatively heavy atomic weight of potassium, insignificant fractionation of the different potassium isotopes occurs.Potassium occurs in two stable isotopes (Ar atoms trapped inside minerals.What simplifies things is that potassium is a reactive metal and argon is an inert gas: Potassium is always tightly locked up in minerals whereas argon is not part of any minerals. So assuming that no air gets into a mineral grain when it first forms, it has zero argon content.The isotopes the KAr system relies on are Potassium (K) and Argon (Ar).

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