| When elements undergo radioactive decay, they don't disappear. They decay into other elements (or into different isotopes of the same element) that are referred to as 'daughter products' of the element undergoing decay. So, if you have a bunch of C14 in something, and a bunch of [whatever C14's daughter product is, i forget] you can add them together, and that's how much C14 there was to start with. And based on the amound that's decayed into daughter products, you can tell how long it's been decaying for. There's still some other sources of error to worry about, but overall it's a very effective method. You can use other elements as well. Uranium, Thorium and Lead all have isotopes that undergo radioactive decay at known rates. |
