Thus, if we start out with 1 gram of the parent isotope, after the passage of 1 half-life there will be 0.5 gram of the parent isotope left.
After the passage of two half-lives only 0.25 gram will remain, and after 3 half lives only 0.125 will remain etc.
For example, an object with a quarter of its original amount (2x1/2) should be roughly 11,460 years old.
In all radiometric procedures there is a specific age range for when a technique can be used.
The realisation that radioactive materials emit rays indicated a constant change of those materials from one element to another.