Why is potassium 40 useful in dating igneous rocks
But consider what happens if the argon came from deep within the Earth, where it was formed by Ar ratio as is found in the atmosphere, and the formula that corrects for atmospheric carbon will not correct for this.
Finally, we must consider the possibility of argon loss.
Argon, on the other hand, is an inert gas; it cannot combine chemically with anything.
As a result under most circumstances we don't expect to find much argon in igneous rocks just after they've formed.
A radioactive isotope is an isotope whose nucleus tends to release particles, radiant energy, or both; Radioactive dating is a technique for determining the age of material by measuring the amount of a particular radioactive isotope the material contain.
If the rock actually contained some argon-40 when it solidified then the calculated age would be too old. What he does is check his calculated age with the ages produced by other dating methods.
And he hopes the rock has remained sealed until the time he collected his sample.
the geologist only needs to measure the relative amounts of potassium-40 and argon-40 in the rock at the present time to be able to calculate an age for the rock.
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.