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.This rare, unstable isotope is produced from ordinary nitrogen 14.In earth's upper atmosphere, on the edge of what is commonly called outer space, light atomic nuclei from unknown sources outside of our solar system traveling at speeds approaching the speed of light called rain down continuously.These isotopes are stable, which is why they are with us today, but unstable isotopes are also present in minute amounts.
Each radioactive isotope decays by a fixed amount, and this amount is called the half-life.
Every time a living being dies a stopwatch starts ticking. is used to determine the age of previously living things based on the abundance of an unstable isotope of carbon.
The isotopic distribution of carbon on the Earth is roughly 99% carbon 12 (with 6 protons and 6 neutrons) and 1% carbon 13 (with 6 protons and 7 neutrons).
The amount of carbon-14 in the atmosphere has not changed in thousands of years.
Even though it decays into nitrogen, new carbon-14 is always being formed when cosmic rays hit atoms high in the atmosphere.