Re: How do you measure the half-life of elements 112,1

Precisely because we know how long they have lasted. If each atom of 
element 112 takes a certain amount of time to decay, we can plot a graph 
of frequency of atoms with that life-time against life-time. We can then 
find the half life - the time in which there is a 50% probability of decay.
The question that I find harder to get my mind around is how we can 
possibly measure the half life of an element which typically takes 
hundereds of thousands of years to decay. The answer is that even in a 
very small piece of, eg. Uranium, there are so many atoms that some will 
decay while we watch.