Radioactive decay and radiometric dating
Most students don't really know how isotopes are used to determine age.
In particular, they have a hard time understanding that different systems are appropriate for different types of radiometric dating and why.
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.
They may ask, "What's the difference between an isotope and an atom?
" Another way of explaining it is that when geologists talk about isotopes, they are talking about one element of differing masses.
The atoms that are involved in radioactive decay are called isotopes.
In reality, every atom is an isotope of one element or another.
Radiometric dating is the method of obtaining a rock's age by measuring the relative abundance of radioactive and radiogenic isotopes.
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.
However, oxygen atoms can have between 8 and 10 neutrons in the nucleus and therefore the isotopes of oxygen have atomic masses of 16, 17, and 18 a.m.u.(and none are radioactive! Samarium (Sm) has 7 naturally occurring isotopes (3 are radioactive).
Remind them that geologists only use certain radioactive isotopes to date rocks.