Argon radiometric dating

If you came back after 1.25 billion years, and assuming nobody has heated the rock or altered it chemically, you would find 1/2 grams of 40K and 1/2 grams of 40Ar/40Ca.

After another 1.25 billion years, you should find 1/4 grams of 40K and 3/4 grams of 40Ar/40Ca.

While such geological complexities pose additional challenges to geochronologists, even "bad" dates can be very useful.

When 40K decays radioactively, it produces both 40Ar (argon) and 40Ca (calcium), with a half-life of 1.25 billion years.

For example, imagine you crsytallize a rock with 1 gram of 40K (and no 40Ar).

Before I begin, there is one set of terms you should be able to distinguish: radiometric dating is a method of estimating the age of geological events using radioactive isotopes in minerals; radioactive dating occurs in the storage room at the nuclear power plant and has very little to do with geology.

Confusion of these terms is a sure sign of geological ignorance.

Chances are, you learned a simplified version of the technique at one point—if you remember your chemistry teacher discussing isotopes, half-lives, hourglasses, well, that was it—but have since removed the lesson to a box labeled "High School Amnesia" in some dark corner of your brain.

If you're reading this now, however, you might be curious to reopen that box in an effort to follow my argument as I answer the title of this post (or, if nothing else, to avoid admitting that chemistry was "not really your thing").For any given rock, each kind of mineral will yield a different age, depending on how quickly the rock cooled.If the rock was reheated at any point, the method no longer provides a straightforward interpretation of the cooling age (hence all dates are termed "apparent ages")." Now, my concern is that to the non-scientist (or even to the experienced scientist that doesn't regularly work with geochronology) this reasoning may seem plausible and end the debate without warrant.But if the failure of the K-Ar dating method is so obvious, why do scientists still spend so much money on running samples?If any excess argon becomes trapped in the mineral during crystallization, the mineral will appear older than it actually is; if any argon is lost after the mineral crystallizes, the mineral will appear younger.

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