Concept radiometric dating
In order to determine the age of a geologic material, we must understand the concept of half-life. The definition is: the radioactive isotopes in a system.
The units of half-life are always time (seconds, minutes, years, etc.).
Radioactivity and radioactive decay are spontaneous processes.
Students often struggle with this concept; therefore, it should be stressed that it is impossible to know exactly when each of the radioactive elements in a rock will decay.
I find that entry-level students in my courses get stuck on the term "half-life".
Even if they have been given the definition, they interpret the term to mean one-half the life of the system.
There is no going back -- the process is irreversible. When we pour our popcorn kernels into a popcorn popper, the is no way to know which will pop first.
And once that first kernel pops, it will never be a kernel again..is forever changed! ) Teaching example using popcorn to teach radioactive decay "A variety of a chemical element (strictly, of one particular element) which is distinguished from the other varieties of the element by a different mass number but shares the same atomic number and chemical properties (and so occupies the same position in the periodic table)." That definition may not mean anything to them.
In particular, they have a hard time understanding that different systems are appropriate for different types of radiometric dating and why.
The only way that this can happen is by changing the number of protons in the nucleus (an element is defined by its number of protons).