Age dating of basalt

Finally, ​the argon atoms are counted in a mass spectrometer, a machine with its own complexities.

Three argon isotopes are measured: Ar is determined by comparison to it.

These effects must be corrected, and the process is intricate enough to require computers.

age dating of basalt-1

That is, a fresh mineral grain has its K-Ar "clock" set at zero.

The method relies on satisfying some important assumptions: Given careful work in the field and in the lab, these assumptions can be met.

The rock samples are crushed, in clean equipment, to a size that preserves whole grains of the mineral to be dated, then sieved to help concentrate these grains of the target mineral.

The selected size fraction is cleaned in ultrasound and acid baths, then gently oven-dried.

A precise amount of argon-38 is added to the gas as a "spike" to help calibrate the measurement, and the gas sample is collected onto activated charcoal cooled by liquid nitrogen.

Then the gas sample is cleaned of all unwanted gasses such as H, nitrogen and so on until all that remains are the inert gasses, argon among them.

Because Ar has a very short half-life, it is guaranteed to be absent in the sample beforehand, so it's a clean indicator of the potassium content.

The advantage is that all the information needed for dating the sample comes from the same argon measurement. This method is commonly called "argon-argon dating."The physical procedure for K.

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.

These dating methods have been under constant improvement for more than 50 years.

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