Carbon dating works because all biotic factors absorb carbon from their surroundings. Although the absorption comes to an end at the death of the living organism, the carbon continues to decay. This tells scientists an approximation of when the organism died.
What is carbon dating?
Carbon dating is the process in which (mainly) petrologists use the presence of carbon in an organism to date back to its lifespan and identify when it died off. Because everything that has life absorbs carbon, we are sure carbon dating is an accurate method for determining how long the matter lived.