Argon, an inert gas, is not chemically bonded to neighboring atoms at all, and even minor thermal disturbance allows them to escape.Rubidium-strontium dating is more robust, and uranium-lead dating can survive fairly significant metamorphism without resetting.Since there is now only 1/4 of the original amount of Parentium-123, we know that two half-lives of Parentium-123 have elapsed.
Weathering and metamorphism are the two most common ways to disturb a system.
Potassium-argon dating is very susceptible to resetting because the argon decay products are merely held in place mechanically by surrounding atoms.
4) What is the age a granite intrusion which has an isotopic abundance of P=6.25% and a half-life of 4 million years?
What percentage of this isotope should be found as daughter material in this rock?
Let t stand for time and N(t) stand for the number of atoms at time t .
In calculus terms, we write: d N(t)/dt = -K * N(t) or d N(t)/N(t) = -K dt The minus sign means that each decay decreases the total number of atoms.
This is the only way Parentium-123 decays, and there is no other source of Daughterium-123.
Furthermore, Parentium and Daughterium are so different in chemical properties that they don't otherwise occur together.
A maximum age is the oldest the object can possibly be. But they obviously have to have been made first, so 1920 is the maximum age of the burial.
Suppose, in repaving your driveway, you find a stash of old coins buried in the ground. Of course there are more outlandish explanations, like somebody counterfeiting 1920 coins in 1900 (and successfully anticipating any changes in design in the meantime), or secretly tearing up part of the driveway after 1950, but unless someone comes up with really persuasive evidence, we're justified in ignoring these hypotheses.
It's amazing how often people fail to realize that you can't date materials if they don't have the necessary ingredients. You can't use carbon-14 to date an arrowhead with no carbon in it.