# How does absolute age differ from relative age?

In short, absolute dating is a technique by which isotopes of a certain element are measured and then using a particular decay system (for example, $U - P b$) an age can be constructed. This will give you a number and then you would calculate an associated uncertainty. For example, I may date a zircon mineral by measuring U and Pb and get an age of 2013 $\pm$ 15 Ma ( Ma = million years ago).