There are different methods of radiometric dating that will vary due to the type of material that is being dated.For example, uranium-lead dating can be used to find the age of a uranium-containing mineral.
So, you might say that the 'full-life' of a radioactive isotope ends when it has given off all of its radiation and reaches a point of being non-radioactive.
When the isotope is halfway to that point, it has reached its half-life.
So, we see there are a number of different methods for dating rocks and other non-living things, but what if our sample is organic in nature?
For example, how do we know that the Iceman, whose frozen body was chipped out of glacial ice in 1991, is 5,300 years old?
They release radiation until they eventually become stable isotopes of lead.
These two uranium isotopes decay at different rates. The half-life of the uranium-238 to lead-206 is 4.47 billion years.This process begins as soon as a living thing dies and is unable to produce more carbon-14.Plants produce carbon-14 through photosynthesis, while animals and people ingest carbon-14 by eating plants. Scientists determine the ages of once-living things by measuring the amount of carbon-14 in the material.By anyone's standards, 50 billion years is a long time.In fact, this form of dating has been used to date the age of rocks brought back to Earth from the moon.So, we rely on radiometric dating to calculate their ages.