However, the carbon-14 already in the organism's body continues to decay at a constant rate.
Carbon dating cannot be used on most fossils, not only because they are almost always too old, but also because they rarely contain the original carbon of the organism.
At any given moment all living plants and animals have approximately the same percentage of carbon-14 in their bodies.
When a plant or animal dies it stops bringing in new carbon-14.
Carbon-14 is created from nitrogen-14 in the upper atmosphere of the earth.
Radiation from the sun collides with atoms in the atmosphere.