Because plants use carbon dioxide for photosynthesis, this isotope ends up inside the plant, and because animals eat plants, they get some as well.When a plant or an animal dies, it stops taking in carbon-14.
And this would also include things like trees and plants, which give us paper and cloth.
So, radiocarbon dating is also useful for determining the age of relics, such the Dead Sea Scrolls and the Shroud of Turin.
These differing rates of decay help make uranium-lead dating one of the most reliable methods of radiometric dating because they provide two different decay clocks.
This provides a built-in cross-check to more accurately determine the age of the sample.
With radiocarbon dating, the amount of the radioactive isotope carbon-14 is measured.