Isotopes in carbon dating
With radiocarbon dating, the amount of the radioactive isotope carbon-14 is measured.Compared to some of the other radioactive isotopes we have discussed, carbon-14's half-life of 5,730 years is considerably shorter, as it decays into nitrogen-14.In fact, this form of dating has been used to date the age of rocks brought back to Earth from the moon.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?These two uranium isotopes decay at different rates. The half-life of the uranium-238 to lead-206 is 4.47 billion years.The uranium-235 to lead-207 decay series is marked by a half-life of 704 million years.Carbon-14 is continually being created in the atmosphere due to the action of cosmic rays on nitrogen in the air.Carbon-14 combines with oxygen to create carbon dioxide.
It works because we know the fixed radioactive decay rates of uranium-238, which decays to lead-206, and for uranium-235, which decays to lead-207.
The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state. This process by which an unstable atomic nucleus loses energy by releasing radiation is called radioactive decay.
The thing that makes this decay process so valuable for determining the age of an object is that each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life.
However, rocks and other objects in nature do not give off such obvious clues about how long they have been around.
So, we rely on radiometric dating to calculate their ages.